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Summary

The number of children in Western societies is influenced by various factors such as economic conditions, education levels, housing costs, substance use, and government policies. Key findings include:

- Negative factors affecting fertility:
-- Women's education and labor force participation
-- Economic uncertainty and unemployment
-- High housing costs delaying family formation
-- Delayed childbearing and obesity
-- Lack of supportive family policies and individualism

- Positive factors influencing fertility:
-- Low-cost childcare, paid parental leave, and paternal involvement in childcare
-- Higher household income and religiosity

- Political orientation and number of children:
-- Conservative/right-leaning individuals tend to have more children than liberal/left-leaning counterparts.

- Household income and number of children:
-- Complex relationship with higher-income areas having lower birth rates at the population level, but individual-level factors like sex and income type also play a role.

- Economic crises and fertility:
-- Recessions and economic downturns cause delays in childbearing due to job loss or financial instability.
-- The COVID-19 pandemic affected birth rates differently depending on country-specific contexts and policy responses.

- Housing costs:
-- High housing costs significantly influence age at first birth, delaying family formation among young adults.

- Substance use and fertility:
-- Tobacco smoking reduces female fertility by affecting ovulation and increasing miscarriage risk.
-- Alcohol consumption affects female fecundability in a dose-dependent manner.
-- Cannabis use may reduce sperm count in men and interfere with reproductive processes.

- Parental influence on offspring's reproductive behavior:
-- Low parental socioeconomic status predicts early childbearing in daughters, while higher parental education and income may delay childbearing but increase the likelihood of having more children later on.
-- Intergenerational transmission of family size is evident, with parents' family environment shaping their children's reproductive decisions.

- Government family policies:
-- Subsidized childcare, paid parental leave, and cash benefits have modest but positive effects on fertility rates.
-- No single policy is universally effective in isolation; a comprehensive approach is necessary to address the complex factors influencing family planning.

In conclusion, family planning and the number of children are shaped by a complex interplay of economic, social, educational, and policy-related factors that collectively influence fertility decisions across generations. Understanding these factors can inform policies aimed at supporting families and promoting healthy reproductive outcomes.


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tsitaat:

## Main Factors Influencing Family Planning and Number of Children in Western Societies **Negative factors** (associated with lower fertility) include **women's education and labor force participation, economic uncertainty, unemployment, housing costs, delayed childbearing, obesity, lack of supportive family policies, and value shifts toward individualism**. **Positive factors** (associated with higher fertility) include **free or low-cost childcare, paid parental leave, paternal involvement in childcare, higher household income, and religiosity**.[1][2][3] ### Negative Factors Reducing Fertility **Socioeconomic barriers** represent the most significant constraints on fertility in Western societies. Lower educational attainment and lower household income are associated with reduced fecundability (probability of conception per menstrual cycle).[4][5] A Danish preconception cohort of 10,475 women found that compared to those with the highest education level, fecundability was substantially lower for women with primary/secondary education (FR: 0.73), vocational education (FR: 0.81), and lower tertiary education (FR: 0.87).[5] Similarly, household income below 25,000 DKK monthly was associated with 22% lower fecundability compared to incomes above 65,000 DKK.[5] Figure 1 Associations of Poverty, Educational Level of Women and Men, and Household Income With Fecundability undefined **Economic uncertainty and unemployment** have consistent negative effects on fertility rates. A multinational analysis of 30 OECD countries from 1976-2014 revealed that increases in unemployment significantly reduced fertility rates in both Western European (−0.00256; p [6] **Postponement of childbearing** is driven by multiple factors including women's increased education and labor market participation, effective contraception availability, value changes emphasizing self-fulfillment over procreation, partnership instability, housing costs, and absence of supportive policies.[1][7][8] This delay creates a fundamental conflict between the optimal biological period for reproduction and the time needed to complete education and establish careers.[1] **Lifestyle and environmental factors** also contribute to declining fertility. Obesity negatively affects fertility rates in Western European countries.[6] Environmental exposures to chemicals from fossil fuels, including endocrine disruptors, may be contributing to deteriorating reproductive health, though causality remains under investigation.[9] Additionally, inadequate knowledge of female reproductive aging, particularly among men, contributes to delayed childbearing and subsequent fertility challenges.[2] ### Positive Factors Supporting Higher Fertility **Family-supportive policies** can effectively counter fertility decline. Countries with improved provision of free or low-cost childcare, paid parental leave, and higher paternal contributions to childcare have seen increases in total fertility rates despite continuing trends toward older age at first birth.[2] Sweden increased its total fertility rate from 1.5 in the late 1990s to 1.9 in 2019 through such policies, though similar approaches had limited success in Singapore and Taiwan.[10] **Higher socioeconomic status** shows complex relationships with fertility. While globally education correlates negatively with fertility, Western Europe shows a unique pattern where total fertility rate actually increases with education and decreases with religiosity.[3] At the individual level, higher household income is associated with better fecundability.[5] **Religiosity** positively correlates with fertility rates across most global regions, potentially counteracting ongoing fertility decline in some areas.[3] ### Key Studies Mills et al. (2011) conducted a systematic PRISMA review examining reasons for birth postponement and social policy effectiveness, identifying central drivers including contraception, women's education and employment, value changes, gender equity, partnership changes, housing conditions, and economic uncertainty.[1] Götmark and Andersson (2020) analyzed 141 countries across six global regions, finding that fertility correlates negatively with education, contraceptive prevalence, and GDP per capita, while correlating positively with religiosity. Notably, Western Europe showed unique patterns where fertility increased with education.[3] Jørgensen et al. (2023) followed 10,475 Danish women in a preconception cohort, demonstrating that both lower educational attainment and lower household income were independently associated with reduced fecundability, with effects persisting after adjustment for confounders.[5] Anderson and Hickey (2023) reviewed demographic transitions in high-income countries, noting that while total fertility rates remain below replacement levels, some countries with greater prosperity and supportive policies are experiencing modest increases despite older maternal age.[2] Aitken and Norman (2025) examined the interplay of social, environmental, and genetic forces, arguing that prolonged subreplacement fertility may permanently compromise human fecundity through reduced evolutionary selection pressure, increased reliance on assisted reproductive technology, and environmental pollutant exposure.[7] ## References 1. Why Do People Postpone Parenthood? Reasons and Social Policy Incentives. Mills M, Rindfuss RR, McDonald P, te Velde E. Human Reproduction Update. 2011 Nov-Dec;17(6):848-60. doi:10.1093/humupd/dmr026. 2. Reproduction in a Changing World. Anderson RA, Hickey M. Fertility and Sterility. 2023;120(3 Pt 1):415-420. doi:10.1016/j.fertnstert.2022.12.013. 3. Human Fertility in Relation to Education, Economy, Religion, Contraception, and Family Planning Programs. Götmark F, Andersson M. BMC Public Health. 2020;20(1):265. doi:10.1186/s12889-020-8331-7. 4. Poverty and Social Disadvantage in Women and Men and Fertility Outcomes. Boxem AJ, Mulders AGMGJ, van Rossum I, et al. JAMA Network Open. 2025;8(9):e2532741. doi:10.1001/jamanetworkopen.2025.32741. 5. Socioeconomic Status and Fecundability in a Danish Preconception Cohort. Jørgensen MD, Mikkelsen EM, Hatch EE, et al. Human Reproduction (Oxford, England). 2023;38(6):1183-1193. doi:10.1093/humrep/dead077. 6. Influence of Obesity and Unemployment on Fertility Rates: A Multinational Analysis of 30 Countries From 1976 to 2014. König-Castillo DM, Ott J, König D, et al. Journal of Clinical Medicine. 2022;11(5):1152. doi:10.3390/jcm11051152. 7. Epidemiology of Falling Fertility: The Contribution of Social, Environmental, and Genetic Forces. Aitken RJ, Norman RJ. Fertility and Sterility. 2025;:S0015-0282(25)00264-X. doi:10.1016/j.fertnstert.2025.04.048. 8. Population Decline: Where Demography, Social Science, and Biology Intersect. Aitken RJ. Reproduction (Cambridge, England). 2024;168(1):e240070. doi:10.1530/REP-24-0070. 9. Environmental Factors in Declining Human Fertility. Skakkebæk NE, Lindahl-Jacobsen R, Levine H, et al. Nature Reviews. Endocrinology. 2022;18(3):139-157. doi:10.1038/s41574-021-00598-8. 10. Fertility, Mortality, Migration, and Population Scenarios for 195 Countries and Territories From 2017 to 2100: A Forecasting Analysis for the Global Burden of Disease Study. Vollset SE, Goren E, Yuan CW, et al. Lancet (London, England). 2020;396(10258):1285-1306. doi:10.1016/S0140-6736(20)30677-2.

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**There is a statistical association between political preference on the left-right spectrum and number of children.** Conservative/right-leaning individuals have **higher fertility rates** than liberal/left-leaning individuals, with this gap **widening over time**. However, the available literature does not provide specific data on the association between political orientation and maternal age at first birth. ## Association Between Political Orientation and Number of Children **Conservative/Republican individuals desire and have more children than liberal/Democratic individuals.** A nationally representative study of 67,557 American 12th graders from 1989-2019 found that Republicans consistently desired more children than Democrats, with this difference growing substantially over time—from 0.07 children in 1989-1993 to 0.29 children in 2014-2019.[1] In later periods, Republicans had higher probability of wanting four or more children and lower probability of eschewing parenthood entirely.[1] **Actual completed fertility shows similar patterns.** Analysis of three large datasets (World Value Survey with 152,380 participants, Survey of Health, Ageing and Retirement in Europe with 65,912 participants, and General Social Survey of the United States with ~6,200 participants) demonstrated that right/conservative political attitudes are associated with higher average offspring numbers compared to intermediate attitudes.[2] In European and US surveys specifically, only the political right was associated with above-average number of children.[2] **The pattern has evolved over time.** US data from 1972-2014 shows this association emerged during the 1990s. In the 1970s and 1980s, both political extremes (left and right) had reproductive advantages, but the fertility advantage for left-wing individuals vanished during the 1990s.[2] **Differential fertility has measurable societal impacts.** Data from the General Social Survey indicate that higher-fertility individuals and their children are more conservative on "family values" issues. Over 2004-2018, opposition to same-sex marriage and abortion was 3-4 percentage points more prevalent than it would have been if traditional-family conservatism were independent of family size. As of 2018, differential fertility raised the number of US adults opposed to same-sex marriage by 17%, from 46.9 million to 54.8 million.[3] ## Mechanisms Underlying the Association **Religiosity and gender attitudes explain much but not all of the gap.** Differences in religiosity and attitudes toward gender and childbearing explained Republican-Democrat fertility gaps before 2004. From 2004 onward, these factors attenuated but did not fully explain the partisan differences.[1] **Parenthood itself may increase conservatism.** Cross-cultural evidence from 10 countries (n=2,610) and World Values Survey data (n=426,444) demonstrates that both parenthood and parental care motivation are associated with increased social conservatism globally. Most of the positive association between age and social conservatism is accounted for by parenthood status.[4] **Family ideals directly map onto political attitudes.** Research supports Moral Politics Theory, which posits that individuals' ideals about parenting (strict-father versus nurturant-parent models) serve as conceptual templates for how society should function and predict whether one endorses conservative or progressive positions.[5][6] ## European Context **Childless individuals vote differently in Europe.** Analysis of European Social Survey data from 20 countries (n=37,623) found that childless individuals voted for parties positioned at the Green-Alternative-Libertarian (GAL) pole rather than the Traditional-Authoritarian-Nationalist (TAN) pole of the ideological dimension.[7] ## Limitations Regarding Age at First Birth The available literature does not provide specific statistical data on the relationship between political orientation and maternal age at first birth. While studies document that higher education is associated with later age at first birth, and that political orientation correlates with education levels, direct analysis of political preference and timing of first birth was not found in the searched literature.[8][9] ## References 1. Youth's Political Identity and Fertility Desires. Rackin HM, Gibson-Davis CM. Journal of Marriage and the Family. 2024;86(4):1132-1148. doi:10.1111/jomf.13000. 2. Political Attitude and Fertility: Is There a Selection for the Political Extreme?. Fieder M, Huber S. Frontiers in Psychology. 2018;9:2343. doi:10.3389/fpsyg.2018.02343. 3. Differential Fertility Makes Society More Conservative on Family Values. Vogl TS, Freese J. Proceedings of the National Academy of Sciences of the United States of America. 2020;117(14):7696-7701. doi:10.1073/pnas.1918006117. 4. Experimental and Cross-Cultural Evidence That Parenthood and Parental Care Motives Increase Social Conservatism. Kerry N, Al-Shawaf L, Barbato M, et al. Proceedings. Biological Sciences. 2022;289(1982):20220978. doi:10.1098/rspb.2022.0978. 5. A Moral House Divided: How Idealized Family Models Impact Political Cognition. Feinberg M, Wehling E. PloS One. 2018;13(4):e0193347. doi:10.1371/journal.pone.0193347. 6. Measuring Moral Politics: How Strict and Nurturant Family Values Explain Individual Differences in Conservatism, Liberalism, and the Political Middle. Feinberg M, Wehling E, Chung JM, Saslow LR, Melvær Paulin I. Journal of Personality and Social Psychology. 2020;118(4):777-804. doi:10.1037/pspp0000255. 7. Is There a "Childless Vote" in Europe?. Lönnqvist JE, Ilmarinen VJ. International Journal of Psychology : Journal International De Psychologie. 2023;58(6):512-517. doi:10.1002/ijop.12939. 8. Variations in Reproductive Events Across Life: A Pooled Analysis of Data From 505 147 Women Across 10 Countries. Human Reproduction (Oxford, England). 2019;34(5):881-893. doi:10.1093/humrep/dez015. 9. Increasingly Heterogeneous Ages at First Birth by Education in Southern European and Anglo-American Family-Policy Regimes: A Seven-Country Comparison by Birth Cohort. Rendall M, Aracil E, Bagavos C, et al. Population Studies. 2010;64(3):209-27. doi:10.1080/00324728.2010.512392.

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**There is a well-documented statistical association between household income and number of children, but the relationship is more complex than a simple threshold effect.** At the population level, **higher-income areas have lower birth rates**, and this negative gradient has **steepened dramatically since 2005** in the US. However, at the individual level, the direction of the association depends critically on **sex, the type of income measured, and whether confounders like opportunity cost are controlled**. ## The Population-Level Pattern: Higher Income, Fewer Births A cross-sectional study of **86.7 million US births** (2000–2020) found that the association between county-level income and natality was essentially flat in 2000 (gradient: −0.061; 95% CI: −0.200 to 0.078) but became **strongly negative by 2020** (gradient: −0.572; 95% CI: −0.678 to −0.466).[1] The decline in natality was approximately **twice as large in the highest-income counties** compared with the lowest-income counties. Counterfactual modeling suggested that had natality inequality remained at its 2000 level, there would have been an additional **3.5 million births** (4.1% increase) over the study period.[1] “The natality income gradient changed from −0.061 in 2000 to −0.572 in 2020, reflecting an increase in natality inequality. A negative gradient reflects that natality is lower in higher-income counties compared with lower-income counties.” — Nick Turner, PhD1, et al.Federal Reserve Board of Governors, Washington, DC and other institutions Importantly, this relationship appears **approximately linear across the income distribution** rather than showing a clear threshold. Birth rates decline progressively with each income ventile increase, without a sharp inflection point at a specific income level.[1] ## The Individual-Level Paradox: It Depends on Sex and What Is Measured The relationship between income and fertility differs substantially by sex and by the type of income measured, based on US Census Survey of Income and Program Participation data (2014):[2] - **Men's personal income** is **positively** associated with fertility — higher-earning men have more children - **Women's personal income** is **negatively** associated with fertility — higher-earning women have fewer children - **Family income (net of personal income)** is **positively** associated with fertility for women — women with higher-earning partners have more children - **Family net worth** is **negatively** associated with fertility for both sexes This paradox is explained by the **opportunity cost of childbearing**, which falls disproportionately on women. When the "net price of a child" (including opportunity cost of the mother's time) is statistically controlled, the pure income effect on fertility becomes **positive and significant**. Without this control, the income effect appears negative.[3] ## Swedish Longitudinal Evidence: The Gradient Is Shifting A Swedish register-based study of cohorts born 1940–1970 using lifetime accumulated income found a **strong positive gradient** between income and fertility for men across all cohorts, and a **gradual transformation from negative to positive** for women in more recent cohorts.[4] For men, fertility increased **monotonically** with income. For women, the positive gradient was primarily driven by very low fertility among women with the lowest accumulated incomes. Individuals with 2–4 children had the highest accumulated incomes, while **childless men and women had substantially lower lifetime incomes**.[4] ## Fecundability: A Graded Relationship Without a Sharp Threshold Studies examining biological fecundability (per-cycle probability of conception) show a **graded, dose-response relationship** with household income rather than a discrete threshold: - In a Dutch cohort, household income **[5] - In a Danish cohort of 10,475 women, compared to household income >65,000 DKK/month (~€8,700), fecundability was progressively lower at [6] - In a North American cohort of 8,654 women, household income [7] The following figure illustrates the graded association between poverty, education, and household income with fecundability: Figure 1 Associations of Poverty, Educational Level of Women and Men, and Household Income With Fecundability undefined ## Summary Rather than a single income threshold, the evidence points to a **continuous, approximately linear negative gradient** between area-level income and birth rates that has steepened over time.[1] At the individual level, the relationship is **sex-dependent**: positive for men's income, negative for women's personal income, but positive for partner/family income — reflecting the **opportunity cost trade-off** women face between career advancement and childbearing.[2][3] The literature from multiple countries consistently shows that the relationship is graded rather than threshold-based, with economic insecurity at lower income levels and opportunity costs at higher income levels both contributing to reduced fertility through different mechanisms.[8] ## References 1. Association Between County-Level Natality and Income in the US, 2000-2020. Turner N, Robbins K. JAMA Pediatrics. 2023;177(2):198-202. doi:10.1001/jamapediatrics.2022.4814. 2. Sex Differences in the Association of Family and Personal Income and Wealth With Fertility in the United States. Hopcroft RL. Human Nature (Hawthorne, N.Y.). 2019;30(4):477-495. doi:10.1007/s12110-019-09354-4. 3. The Income--Fertility Relationship: Effect of the Net Price of a Child . Borg MO. Demography. 1989;26(2):301-10. 4. The Relationship Between Life-Course Accumulated Income and Childbearing of Swedish Men and Women Born 1940-70. Kolk M. Population Studies. 2023;77(2):197-215. doi:10.1080/00324728.2022.2134578. 5. Poverty and Social Disadvantage in Women and Men and Fertility Outcomes. Boxem AJ, Mulders AGMGJ, van Rossum I, et al. JAMA Network Open. 2025;8(9):e2532741. doi:10.1001/jamanetworkopen.2025.32741. 6. Socioeconomic Status and Fecundability in a Danish Preconception Cohort. Jørgensen MD, Mikkelsen EM, Hatch EE, et al. Human Reproduction (Oxford, England). 2023;38(6):1183-1193. doi:10.1093/humrep/dead077. 7. Association of Income and Education With Fecundability in a North American Preconception Cohort. Schrager NL, Wesselink AK, Wang TR, et al. Annals of Epidemiology. 2020;50:41-47.e1. doi:10.1016/j.annepidem.2020.07.004. 8. Wealth, Fertility and Adaptive Behaviour in Industrial Populations. Stulp G, Barrett L. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 2016;371(1692):20150153. doi:10.1098/rstb.2015.0153.

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**There is a strong and well-documented statistical association between economic crises and fertility decline.** Fertility is **pro-cyclical** in modern economies — it rises during economic expansions and falls during downturns.[1][2] Crises also **postpone first births**, particularly among young adults under 30, and in some cases this postponement becomes **permanent childlessness**.[3][4] ## Economic Recessions and Birth Rates **The relationship between economic conditions and fertility has fundamentally changed over time.** Before 1970, fertility was actually counter-cyclical (good economic times were associated with lower fertility), but since then it has become **pro-cyclical**, with good economic times associated with higher fertility.[2] This shift means that modern recessions consistently depress birth rates. The effects operate through several mechanisms: **economic uncertainty, falling income, housing market declines, rising enrollment in higher education, and declining marriage rates**.[1] Unemployment is the single most important economic indicator — a multinational analysis of 30 OECD countries (1976–2014) found that increases in unemployment significantly reduced fertility rates in both Western European (−0.00256; p [5] However, the aggregate effects are typically **relatively small (a few percentage points) and of short duration**, primarily influencing the timing rather than the quantum of childbearing. Major long-term fertility shifts often continue seemingly uninterrupted during recessions — including during the Great Depression of the 1930s and the oil shock crises of the 1970s.[1] ## Impact on Age at First Birth and Postponement **Economic crises disproportionately delay first births among young adults.** A study of 14 European countries (1970–2005) found that adverse economic conditions and high unemployment **significantly reduce first birth hazards among men and women below age 30**, particularly among the higher educated. After age 30, economic context continued to affect men's first birth hazards but **not women's**, suggesting that women over 30 are less willing to further delay childbearing regardless of economic conditions.[4] **Critically, postponement during recessions can become permanent.** Using over 140 million US birth records (1975–2010), Currie and Schwandt found that women in their **early 20s** are most affected. A one percentage point increase in the average unemployment rate experienced between ages 20–24 reduced short-run fertility by **6 conceptions per 1,000 women**, but when these women were followed to age 40, the total loss grew to **14.2 conceptions per 1,000 women**. This long-run effect was driven largely by women who **remained permanently childless** — they did not have first births or any higher-order births.[3] ## The 2008 Great Recession The Great Recession brought a **sharp halt to the previous decade of rising fertility rates** in most developed countries.[1] In the United States, the total fertility rate declined steadily from 2007, reaching **1.73 children in 2018** — the lowest level since the 1970s.[6] Total intended parity also declined (from 2.26 in 2006–2010 to 2.16 in 2013–2017), and the proportion intending to remain childless increased, indicating that the decline was not purely a timing effect.[6] The mean age at first birth in the US rose from approximately 25 in 2007 to **27.3 in 2021**.[7] ## The COVID-19 Pandemic The COVID-19 pandemic produced a **sharp but heterogeneous fertility decline**. Across 24 European countries, a **−14.1% decline in live births** was observed in January 2021 (9–10 months after the first wave peaks and lockdowns), with the duration of lockdowns being the strongest predictor of this decline.[8] Southern European countries were particularly affected: Italy (−9.1%), Spain (−8.4%), and Portugal (−6.6%).[9] In the US, the initial response differed by nativity: **60% of the 2020 fertility decline was driven by reductions in births to foreign-born mothers** (who comprised only 22% of births). Among US-born mothers, a surprising **"baby bump"** occurred — births fell by 31,000 in 2020 but increased by 71,000 in 2021, marking the first reversal in declining fertility since the Great Recession. This bump was most pronounced for **first births and women under 25**, suggesting some women started families earlier during the pandemic.[10] In Italy, the pandemic's economic consequences directly affected fertility plans: individuals who suffered negative income shocks or had negative expectations about future income and occupation were **more likely to abandon their pre-pandemic fertility plans**, and this effect persisted across both early and later phases of the pandemic.[11] ## Wars and Geopolitical Crises **Armed conflicts generally reduce fertility during the active phase**, followed by a post-conflict rebound.[12] Mechanisms include spousal separation, reduced marriage rates, lower fecundity, and increased spontaneous abortion (especially when famine coexists).[12] In Cambodia, fertility decreased by approximately **one-third** from pre-civil war levels during 1975–79.[12] A recent study on Ukraine found that **geopolitical uncertainty following the Crimean crisis (2014) significantly reduced fertility rates**, with households exhibiting precautionary behavior in their fertility decisions. In a low-fertility regime, geopolitical uncertainty proved to be a crucial predictor of fertility behavior.[13] The Rwandan genocide (1994) demonstrated heterogeneous effects: women who lost a child during the genocide showed a strong **child replacement effect** (increased subsequent fertility), while those who experienced sibling death had **lower post-genocide fertility** in both the short and long run.[14] ## A Meta-Analytic Perspective on Employment Instability A European meta-analysis synthesizing research findings on employment instability and fertility confirmed a **nonnegligible negative effect** overall, with important nuances:[15] - **Men's unemployment** is more detrimental to fertility than men's time-limited employment - **Women's fixed-term contracts** are the most detrimental form of employment instability for fertility - The negative effect has become **stronger over time** and is **more severe in Southern European countries**, where social protection for families and the unemployed is least generous - Failing to account for income and partner characteristics leads to an **overestimation** of the negative effect ## Summary A systematic review of 50 studies on fertility after disasters found an **overall negative impact** on fertility across disaster types, though weather-related physical disasters occasionally produced small increases.[16] The evidence consistently shows that crises reduce fertility primarily through postponement of first births among young adults, with the degree of impact modulated by the strength of social safety nets and family policies. The most concerning finding is that recession-induced postponement among women in their early 20s often does not fully recover, contributing to **permanently lower completed fertility**.[3] ## References 1. Economic Recession and Fertility in the Developed World. Sobotka T, Skirbekk V, Philipov D. Population and Development Review. 2011;37(2):267-306. doi:10.1111/j.1728-4457.2011.00411.x. 2. The Changing Relationship Between Unemployment and Total Fertility. Karaman Örsal DD, Goldstein JR. Population Studies. 2018;72(1):109-121. doi:10.1080/00324728.2017.1404624. 3. Short- And Long-Term Effects of Unemployment on Fertility. Currie J, Schwandt H. Proceedings of the National Academy of Sciences of the United States of America. 2014;111(41):14734-9. doi:10.1073/pnas.1408975111. 4. Economic Recession and First Births in Europe: Recession-Induced Postponement and Recuperation of Fertility in 14 European Countries Between 1970 and 2005. Neels K, Theunynck Z, Wood J. International Journal of Public Health. 2013;58(1):43-55. doi:10.1007/s00038-012-0390-9. 5. Influence of Obesity and Unemployment on Fertility Rates: A Multinational Analysis of 30 Countries From 1976 to 2014. König-Castillo DM, Ott J, König D, et al. Journal of Clinical Medicine. 2022;11(5):1152. doi:10.3390/jcm11051152. 6. Recent Trends in U.S. Childbearing Intentions. Hartnett CS, Gemmill A. Demography. 2020;57(6):2035-2045. doi:10.1007/s13524-020-00929-w. 7. Management of Pregnancy (2023). Colleen C. Blosser MSN RN, Michael Bybel DO FAAFP, Alicia Christy MD MHSCR, et al. Department of Veterans Affairs. 8. Impact of the First Wave of the COVID-19 Pandemic on Birth Rates in Europe: A Time Series Analysis in 24 Countries. Pomar L, Favre G, de Labrusse C, et al. Human Reproduction (Oxford, England). 2022;37(12):2921-2931. doi:10.1093/humrep/deac215. 9. Early Assessment of the Relationship Between the COVID-19 Pandemic and Births in High-Income Countries. Aassve A, Cavalli N, Mencarini L, Plach S, Sanders S. Proceedings of the National Academy of Sciences of the United States of America. 2021;118(36):e2105709118. doi:10.1073/pnas.2105709118. 10. The COVID-19 Baby Bump in the United States. Bailey MJ, Currie J, Schwandt H. Proceedings of the National Academy of Sciences of the United States of America. 2023;120(34):e2222075120. doi:10.1073/pnas.2222075120. 11. Fertility Plans in the Early Times of the COVID-19 Pandemic: The Role of Occupational and Financial Uncertainty in Italy. Luppi F, Arpino B, Rosina A. PloS One. 2022;17(12):e0271384. doi:10.1371/journal.pone.0271384. 12. The Effects of Armed Conflict on the Health of Women and Children. Bendavid E, Boerma T, Akseer N, et al. Lancet (London, England). 2021;397(10273):522-532. doi:10.1016/S0140-6736(21)00131-8. 13. Fertility Behaviour Under Geopolitical Uncertainty: Evidence From Ukraine. Saha J. Economics and Human Biology. 2026;61:101594. doi:10.1016/j.ehb.2026.101594. 14. The Effects of Conflict on Fertility: Evidence From the Genocide in Rwanda. Kraehnert K, Brück T, Di Maio M, Nisticò R. Demography. 2019;56(3):935-968. doi:10.1007/s13524-019-00780-8. 15. Employment Instability and Fertility in Europe: A Meta-Analysis. Alderotti G, Vignoli D, Baccini M, Matysiak A. Demography. 2021;58(3):871-900. doi:10.1215/00703370-9164737. 16. Human Fertility After a Disaster: A Systematic Literature Review. Lee DS, Batyra E, Castro A, Wilde J. Proceedings. Biological Sciences. 2023;290(1998):20230211. doi:10.1098/rspb.2023.0211.

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Among the material and economic factors influencing first births, **housing costs and housing market conditions** are the single most impactful material asset-related factor, with expensive housing markets delaying first births by **3–4 years** even after controlling for education, ethnicity, and labor force participation.[1] However, **education and women's labor force participation** remain the strongest overall predictors of reproductive timing, with housing operating as an important but secondary factor within a complex decision-making structure.[2] ## Hierarchy of Factors Affecting First Birth Timing A systematic review following PRISMA methodology identified the central reasons for postponement of first births in Western societies, ranked by strength of evidence:[2] 1. **Women's education and labor force participation** — the strongest and most consistently documented factor. Women with low education had **7-fold higher odds** of first birth before age 24 compared to highly educated women (OR 7.0; 95% CI: 5.3–9.3). The "parenthood wage penalty" — predicted income loss from early childbearing — is a powerful driver of delayed fertility, particularly among high-SES individuals.[3][4] 2. **Housing conditions and costs** — the most important material asset factor (discussed in detail below). 3. **Economic uncertainty and employment security** — the husband's employment security and stable housing arrangements appear to be the **most important factors** for a married couple's fertility decisions in low-fertility settings like South Korea.[5] 4. **Partnership formation and stability** — partnership changes and delayed marriage directly delay first births.[2] 5. **Contraceptive access and value changes** — enabling factors that interact with all of the above.[2] ## Housing: The Dominant Material Factor **Housing costs and mortgage burden** Living in an expensive housing market delays first births by **3–4 years** after controlling for education, ethnicity, and labor market participation, based on analysis of 25 US metropolitan areas using American Community Survey data (2006–2008).[1] However, the relatively modest fit of individual-level models suggests that housing is one component within a complex decision-making structure involving fertility, labor force participation, and housing market entry simultaneously.[1] **Mortgage debt specifically reduces fertility intentions.** A Chinese study of 7,512 adults found that housing mortgage burden was **negatively associated** with fertility intention, and this was one of the primary mechanisms through which housing status affected childbearing decisions.[6] In Europe, the economic consequences of housing costs operate through similar channels — individuals who suffered negative income shocks (often housing-related) were more likely to **abandon pre-existing fertility plans**.[7] **Homeownership and the transition to parenthood** Traditionally, homeownership was positively linked to the transition to parenthood — couples preferred to become homeowners before having their first child. However, British longitudinal data (1991–2016) shows this relationship has **fundamentally changed**: the likelihood of becoming a parent has declined among homeowners while remaining stable among private renters, making the two groups increasingly similar in their likelihood of entering parenthood. This reflects the reality of "Generation Rent," where rising housing unaffordability has undermined the traditional sequencing of homeownership before parenthood.[8] **Housing size and dwelling type** Longitudinal US data supports the prediction that **higher fertility is associated with larger dwellings**.[9] In tight housing markets, apartment dwellers reduced their fertility while house dwellers did not, consistent with the utility-cost theory of fertility — the marginal cost of an additional child is higher in constrained living spaces.[9] Increasing population density at the macro level is also robustly associated with declining fertility rates across 174 countries over 69 years (1950–2019), even after controlling for socioeconomic variables.[10] ## Financial Hardship Across the Life Course A North American preconception cohort (PRESTO, n=6,377) found that **adult financial hardship** was the most sensitive period for fertility effects, reducing fecundability by 17% (FR: 0.83; 95% CI: 0.77–0.90). Critically, the effect was **cumulative**: individuals who experienced financial hardship in both childhood and adulthood had even lower fecundability (FR: 0.77; 95% CI: 0.64–0.93) than those experiencing adult hardship alone.[13] ## Summary Table | Factor | Effect on First Birth Timing | Effect on Number of Children | Strength of Evidence | References | |---|---|---|---|---| | Women's education | Strongest predictor; delays first birth by 5–10+ years between lowest and highest groups | Higher education → fewer children | Very strong (multiple large cohorts) | [1-2] | | Housing costs/mortgage | Delays first birth by 3–4 years in expensive markets | Mortgage burden reduces fertility intentions | Strong (multiple countries) | [3-4] | | Housing size/type | Apartment living constrains fertility in tight markets | Larger dwellings associated with higher fertility | Moderate (older studies) | [5] | | Employment security (husband's) | Delays first birth when insecure | Among the most important factors for couple fertility | Strong (European/Asian data) | [6-7] | | Financial opportunity cost (women's income) | Higher potential income → later first birth | Higher personal income → fewer children for women | Strong (Finnish register data, n=47,678) | [8-9] | | Homeownership | Traditionally positive; now weakening | Declining association in "Generation Rent" | Moderate-strong (UK longitudinal) | [10] | | Cumulative financial hardship | Not directly studied for timing | Reduces fecundability by 17–23% | Moderate (preconception cohort) | [11] | The key insight from the literature is that these factors do not operate independently — they form an interconnected decision-making structure where **education drives labor force participation, which drives income, which determines housing affordability, which influences fertility timing**.[2][4] Housing is the most important single material asset factor, but it is embedded within this broader socioeconomic cascade. ## References 1. Do Women Delay Family Formation in Expensive Housing Markets?. Clark WA. Demographic Research. 2012;27(1):1-24. doi:10.4054/DemRes.2012.27.1. 2. Why Do People Postpone Parenthood? Reasons and Social Policy Incentives. Mills M, Rindfuss RR, McDonald P, te Velde E. Human Reproduction Update. 2011 Nov-Dec;17(6):848-60. doi:10.1093/humupd/dmr026. 3. Socioeconomic Position and Reproduction: Findings From the Australian Longitudinal Study on Women's Health. Holowko N, Jones M, Tooth L, Koupil I, Mishra GD. Maternal and Child Health Journal. 2018;22(12):1713-1724. doi:10.1007/s10995-018-2567-1. 4. Financial Opportunity Costs and Deaths Among Close Kin Are Independently Associated With Reproductive Timing in a Contemporary High-Income Society. Berg V, Lawson DW, Rotkirch A. Proceedings. Biological Sciences. 2020;287(1919):20192478. doi:10.1098/rspb.2019.2478. 5. Socioeconomic Differentials in Fertility in South Korea. Lim S. Demographic Research. 2021 Jan-Jun;44:941-978. doi:10.4054/demres.2021.44.39. 6. Does Inhabitant's Fertility Intention Respond to Housing Status in the Urban Built Environment: Evidence From China. Zhuang X, Li Q, Su T, et al. Frontiers in Public Health. 2025;13:1328329. doi:10.3389/fpubh.2025.1328329. 7. Fertility Plans in the Early Times of the COVID-19 Pandemic: The Role of Occupational and Financial Uncertainty in Italy. Luppi F, Arpino B, Rosina A. PloS One. 2022;17(12):e0271384. doi:10.1371/journal.pone.0271384. 8. The Changing Association Between Homeownership and the Transition to Parenthood. Tocchioni V, Berrington A, Vignoli D, Vitali A. Demography. 2021;58(5):1843-1865. doi:10.1215/00703370-9420322. 9. The Relationship Between Apartment Living and Fertility for Blacks, Mexican-Americans, and Other Americans in Racine, Wisconsin. Curry JP, Scriven GD. Demography. 1978;15(4):477-85. 10. Increasing Population Densities Predict Decreasing Fertility Rates Over Time: A 174-Nation Investigation. Rotella A, Varnum MEW, Sng O, Grossmann I. The American Psychologist. 2021;76(6):933-946. doi:10.1037/amp0000862. 11. Sex Differences in the Association of Family and Personal Income and Wealth With Fertility in the United States. Hopcroft RL. Human Nature (Hawthorne, N.Y.). 2019;30(4):477-495. doi:10.1007/s12110-019-09354-4. 12. The Reproductive Ecology of Industrial Societies, Part II : The Association Between Wealth and Fertility. Stulp G, Sear R, Schaffnit SB, Mills MC, Barrett L. Human Nature (Hawthorne, N.Y.). 2016;27(4):445-470. doi:10.1007/s12110-016-9272-9. 13. Life Course Financial Hardship and Fecundability in a North American Preconception Cohort Study. Hoffman MN, Ncube CN, Murray EJ, et al. Epidemiology (Cambridge, Mass.). 2025;:00001648-990000000-00397. doi:10.1097/EDE.0000000000001900. 14. Variations in Reproductive Events Across Life: A Pooled Analysis of Data From 505 147 Women Across 10 Countries. Human Reproduction (Oxford, England). 2019;34(5):881-893. doi:10.1093/humrep/dez015.

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**Substance use has well-documented statistical associations with fertility outcomes, though the effects vary by substance type and sex.** **Tobacco smoking** has the strongest and most consistent negative effect, increasing infertility risk by **60% (OR 1.60)** and causing conception delays of **54% longer** in smokers versus non-smokers.[1][2] **Alcohol** shows a dose-dependent negative association with female fecundability, with heavy drinking (>6 drinks/week) reducing conception odds by **40–50%**.[3][4] **Cannabis** effects are more mixed, with some studies showing reduced fecundability while others show no association.[5][6] ## Tobacco Smoking **Effect on fertility and fecundability** Tobacco smoking has the most robust evidence for negative reproductive effects. According to the American Society for Reproductive Medicine (ASRM), a meta-analysis of 12 studies (10,928 exposed vs. 19,179 unexposed women) found:[1][2] - Overall infertility risk: **OR 1.60 (95% CI: 1.34–1.91)** - Conception delay >1 year: **OR 1.42 (95% CI: 1.27–1.58)** in cohort studies - Infertility in case-control studies: **OR 2.27 (95% CI: 1.28–4.02)** - Conception delay >12 months was **54% higher** for smokers than non-smokers - **Dose-dependent effect**: increasing delay correlates with increasing daily cigarette consumption **Effect on number of children and age at first birth** A Swiss population-based study (n=6,711) found paradoxical associations:[7] - **Fewer children**: Current female smokers had 1.38 children vs. 1.58 for never-smokers (p[1] Anti-Müllerian hormone (AMH) levels are **44% lower** in current smokers compared to never-smokers, and AMH declines **21% faster per year** in smokers.[1] In men, smoking affects spermatogenesis through oxidative stress and apoptosis in testicular tissue.[8] ## Alcohol **Effect on female fecundability** A systematic review and dose-response meta-analysis of 19 studies (98,657 women) found:[4] - Overall fecundability reduction: **RR 0.87 (95% CI: 0.78–0.95)** for drinkers vs. non-drinkers - Light drinkers (≤12.5 g/day): **RR 0.89 (95% CI: 0.82–0.97)** - Moderate-heavy drinkers (>12.5 g/day): **RR 0.77 (95% CI: 0.61–0.94)** - **Linear dose-response**: Each 12.5 g/day increase associated with RR 0.98 (95% CI: 0.97–0.99) The timing of alcohol consumption within the menstrual cycle matters significantly. Heavy drinking (>6 drinks/week) during the **luteal phase** reduced fecundability by **49% (FOR 0.51; 95% CI: 0.29–0.89)**, and during the **ovulatory window** by **61% (FOR 0.39; 95% CI: 0.19–0.72)**.[3] **Effect on male fertility** In contrast to women, pooled data from Danish and North American preconception cohorts (2,679 couples) found **little evidence** of an association between male alcohol consumption and reduced fecundability.[9] However, chronic alcohol dependence in males is associated with lower sperm counts, motility, morphology, seminal fluid volume, and testosterone levels.[5] **Effect on number of children** A 33-year Finnish twin follow-up study (>3,500 twin pairs) found a **U-shaped relationship**:[10] - Both **abstinence** and **heavier drinking** at ages 18–25 predicted lifetime childlessness - Among those who had children, heavier drinking predicted **smaller family size** - These associations persisted in within-pair analyses of monozygotic twins, ruling out familial confounds **Effect on reproductive timing** Alcohol use disorder (AUD) is associated with **delayed reproduction** or no reproduction, while parental AUD is associated with **early reproduction**.[11] This suggests that AUD may delay reproductive onset through biological impairment or psychosocial mediators such as delays in role transitions. ## Cannabis (Marijuana) **Effect on fertility** The evidence on cannabis is more mixed than for tobacco or alcohol:[5][12] - One study found infertility prevalence increased in ovulatory cannabis users: **RR 1.7 (95% CI: 1.0–3.0)** - Men who smoke cannabis have **29% lower sperm counts** with a dose-dependent effect - However, data from the National Survey of Family Growth and PRESTO cohort showed **no association** between male or female cannabis use and time to pregnancy A prospective cohort study of 1,228 women with a history of pregnancy loss found preconception cannabis use was associated with **reduced fecundability (FOR 0.59; 95% CI: 0.38–0.92)**, despite increased intercourse frequency.[6] **Biological mechanisms** Cannabis affects the endocannabinoid system, which plays a role in regulating reproduction. Effects include:[12][13] - Altered reproductive hormones and menstrual cyclicity - Disturbed folliculogenesis and ovulation - In males: erectile dysfunction, abnormal spermatogenesis, testicular atrophy - In females: abnormal embryo implantation and development The ASRM and ACOG recommend that women who are pregnant or may become pregnant should **discontinue cannabis use** due to adverse effects on fetal neurodevelopment.[5] ## Other Recreational Drugs **Opioids, amphetamines, and cocaine** Substance abuse is a recognized cause of male hypogonadism:[8] - **Opioids** reduce testosterone production by interfering with hypothalamic-pituitary function - **Anabolic-androgenic steroids** suppress gonadotropin secretion, causing hypogonadism - **Amphetamines** alter spermatogenesis through oxidative stress One study found that women who had used **marijuana regularly** or **cocaine** actually had **shorter time to conception** than non-users — a counterintuitive finding that may reflect confounding by sexual behavior patterns rather than a biological effect.[14] The use of non-prescription and recreational drugs before conception is associated with reduced fertility in both men and women, and during pregnancy is associated with increased risk of fetal death, low birth weight, and preterm birth.[15] ## Summary Table | Substance | Effect on Female Fertility | Effect on Male Fertility | Effect on Number of Children | Effect on Age at First Birth | References | |---|---|---|---|---|---| | **Tobacco** | OR 1.60 for infertility; 54% longer time to conception | Reduced sperm parameters; oxidative damage | Fewer children (1.38 vs. 1.58) | Earlier first birth (26.7 vs. 26.9 years) |[1-3] | | **Alcohol (heavy)** | RR 0.77 for fecundability; 40–50% reduction in luteal/ovulatory phases | Chronic use: lower sperm count, motility, testosterone | U-shaped: abstinence and heavy use both predict fewer children | AUD predicts delayed reproduction | [4-6] | | **Cannabis** | Mixed: RR 1.7 for infertility in some studies; no effect in others | 29% lower sperm counts (dose-dependent) | Limited data | Limited data | [7-8] | | **Opioids** | Limited data | Hypogonadism; reduced testosterone | Limited data | Limited data | [9] | | **Cocaine** | Paradoxically shorter time to conception (likely confounded) | Limited data | Limited data | Limited data | [10] | [5][3][4][9][7][6][8][10][14][11] ## Key Clinical Implications The ASRM recommends that couples attempting pregnancy should be counseled to:[5][1][15] - **Avoid tobacco smoking** — the most consistently harmful substance for fertility - **Limit alcohol** to moderate levels (<2 drinks/day); higher consumption should be avoided - **Discontinue cannabis** — particularly for women who are pregnant or may become pregnant - **Stop all recreational drug use** before conception Importantly, substance use effects on fertility are often reversible with cessation, making preconception counseling a critical intervention point. [8][18] ## References 1. Tobacco or Marijuana Use and Infertility: A Committee Opinion. Fertility and Sterility. 2024;121(4):589-603. doi:10.1016/j.fertnstert.2023.12.029. 2. Smoking and Infertility. Fertility and Sterility. 2006;86(5 Suppl 1):S172-7. doi:10.1016/j.fertnstert.2006.08.018. 3. The Association Between Alcohol Intake and Fecundability During Menstrual Cycle Phases. Anwar MY, Marcus M, Taylor KC. Human Reproduction (Oxford, England). 2021;36(9):2538-2548. doi:10.1093/humrep/deab121. 4. Female Alcohol Consumption and Fecundability: A Systematic Review and Dose-Response Meta-Analysis. Fan D, Liu L, Xia Q, et al. Scientific Reports. 2017;7(1):13815. doi:10.1038/s41598-017-14261-8. 5. Optimizing Natural Fertility: A Committee Opinion. Penzias A, Azziz R, Bendikson K, et al. Fertility and Sterility. 2022;117(1):53-63. doi:10.1016/j.fertnstert.2021.10.007. 6. Cannabis Use While Trying to Conceive: A Prospective Cohort Study Evaluating Associations With Fecundability, Live Birth and Pregnancy Loss. Mumford SL, Flannagan KS, Radoc JG, et al. Human Reproduction (Oxford, England). 2021;36(5):1405-1415. doi:10.1093/humrep/deaa355. 7. Impact of Smoking on Fertility and Age of Menopause: A Population-Based Assessment. Oboni JB, Marques-Vidal P, Bastardot F, Vollenweider P, Waeber G. BMJ Open. 2016;6(11):e012015. doi:10.1136/bmjopen-2016-012015. 8. Substance Abuse and Male Hypogonadism. Duca Y, Aversa A, Condorelli RA, Calogero AE, La Vignera S. Journal of Clinical Medicine. 2019;8(5):E732. doi:10.3390/jcm8050732. 9. Male Alcohol Consumption and Fecundability. Høyer S, Riis AH, Toft G, et al. Human Reproduction (Oxford, England). 2020;35(4):816-825. doi:10.1093/humrep/dez294. 10. Alcohol Consumption at Age 18-25 and Number of Children at a 33-Year Follow-Up: Individual and Within-Pair Analyses of Finnish Twins. Rose RJ, Latvala A, Silventoinen K, Kaprio J. Alcoholism, Clinical and Experimental Research. 2022;46(8):1552-1564. doi:10.1111/acer.14886. 11. Alcohol Use Disorder and Parental Alcohol Use Disorder as Predictors of Reproductive Timing. Blake A, Smyth H, Sternberg A, Waddell J, Chassin L. Journal of Studies on Alcohol and Drugs. 2020;81(5):575-583. 12. Impact of Cannabinoids on Pregnancy, Reproductive Health, and Offspring Outcomes. Lo JO, Hedges JC, Girardi G. American Journal of Obstetrics and Gynecology. 2022;227(4):571-581. doi:10.1016/j.ajog.2022.05.056. 13. Cannabis and Cannabinoids in Reproduction and Fertility: Where We Stand. Fonseca BM, Rebelo I. Reproductive Sciences (Thousand Oaks, Calif.). 2022;29(9):2429-2439. doi:10.1007/s43032-021-00588-1. 14. Fertility and Use of Cigarettes, Alcohol, Marijuana, and Cocaine. Joesoef MR, Beral V, Aral SO, Rolfs RT, Cramer DW. Annals of Epidemiology. 1993;3(6):592-4. doi:10.1016/1047-2797(93)90080-n. 15. Preconception Lifestyle Advice for People With Infertility. Boedt T, Vanhove AC, Vercoe MA, et al. The Cochrane Database of Systematic Reviews. 2021;4:CD008189. doi:10.1002/14651858.CD008189.pub3. 16. Does Moderate Alcohol Consumption Affect Fertility? Follow Up Study Among Couples Planning First Pregnancy. Jensen TK, Hjollund NH, Henriksen TB, et al. BMJ (Clinical Research Ed.). 1998;317(7157):505-10. doi:10.1136/bmj.317.7157.505. 17. Adult and Prenatal Exposures to Tobacco Smoke as Risk Indicators of Fertility Among 430 Danish Couples. Jensen TK, Henriksen TB, Hjollund NH, et al. American Journal of Epidemiology. 1998;148(10):992-7. doi:10.1093/oxfordjournals.aje.a009576. 18. Smoke, Alcohol and Drug Addiction and Male Fertility. Sansone A, Di Dato C, de Angelis C, et al. Reproductive Biology and Endocrinology : RB&E. 2018;16(1):3. doi:10.1186/s12958-018-0320-7.