30 Supported by research
Global fertility is projected to decline to approximately 1.8 births per woman by 2050 and 1.6 by 2100.
"Global fertility is projected to keep falling reaching around 1.8 by 2050 and 1.6 by 2100." (said at 0:05:03)
The speaker's statement accurately reflects demographic projections from the Global Burden of Disease (GBD) studies published in The Lancet. In the GBD reference forecasting models, the global total fertility rate (TFR) is projected to decline from current levels to approximately 1.8 by 2050 (estimated at 1.83 in the GBD 2021 analysis) and approximately 1.6 by 2100 (estimated at 1.66 in GBD 2017 and 1.59 in GBD 2021).
By 2100, only six countries are projected to remain at or above the replacement fertility level.
"By 2100 only six countries are expected to still be at or above replacement level." (said at 0:05:15)
The statement accurately reflects findings from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 demographic forecasting analysis published in The Lancet (2024). The study modelled global fertility trends across 204 countries and territories to 2100 under reference and alternative scenarios. In the reference forecast, the global total fertility rate (TFR) was projected to fall from 2.21 in 2021 to 1.59 in 2100, leaving only six countries (Samoa, Somalia, Tonga, Niger, Chad, and Tajikistan; 2.9%) with fertility rates at or above replacement level (TFR ≥ 2.1 livebirths per female), while 198 countries and territories (97.1%) are projected to fall below replacement level.
- supports: Fertility, mortality, migration, and population scenarios for 195 countries and territorie… (The Lancet 2020) · cited 1521x in the literature
"By 2050, 151 countries were forecasted to have a TFR lower than the replacement level (TFR <2·1), and 183 were forecasted to have a TFR lower than replacement by 2100." (abstract, findings, passage verified)
openalexfull study (doi) - supports: Global fertility in 204 countries and territories, 1950–2021, with forecasts to 2100: a co… (The Lancet 2024) · cited 611x in the literature
"To forecast future fertility up to 2100, our Institute for Health Metrics and Evaluation (IHME) forecasting model was based on projections of completed cohort fertility at age 50 years (CCF50; the average number of children born over time to females from a specified birth cohort), which yields more stable and accurate measures of fertility than directly modelling TFR." (abstract, methods, passage verified)
openalexfull study (doi)
The United States recorded a record-low fertility rate of 1.6 births per woman in 2024.
"The US recorded its lowest ever fertility rate of 1.6 births per woman in 2024." (said at 0:05:20)
According to vital statistics from the CDC's National Center for Health Statistics (NCHS), the United States total fertility rate dropped to approximately 1.62 births per woman (1,621.0 births per 1,000 women), representing the lowest total fertility rate ever recorded in national vital statistics.
Approximately 710,000 fewer children were born in the United States in the past year compared to the peak in 2007.
"Around 710,000 fewer children were born in the US last year compared to the nation's peak in 2007." (said at 0:05:26)
According to National Vital Statistics System (NVSS) data published by the Centers for Disease Control and Prevention (CDC), registered births in the United States reached an all-time peak of 4,316,233 in 2007. By 2023, annual US births had dropped to approximately 3.60 million (provisional count of ~3,596,000), representing an ongoing decline of over 710,000 to 720,000 births relative to the 2007 peak.
- supports: Births: final data for 2007. (PubMed 2010) · cited 422x in the literature
"A total of 4,316,233 births were registered in the United States in 2007, the largest number of births ever reported." (abstract, results, passage verified)
openalex - supports: Recent decline in births in the United States, 2007-2009. (PubMed 2011) · cited 20x in the literature
"The number of births in the United States reached an all-time high of 4,316,233 in 2007, but that number has since fallen." (abstract, key findings, passage verified)
openalex
Since 2007, the general fertility rate in the United States has fallen by 23%.
"Since 2007 the general fertility rate has declined by 23%" (said at 0:05:33)
According to vital statistics reports from the National Center for Health Statistics (NCHS), the general fertility rate (GFR) in the United States peaked in 2007 at approximately 69.3 to 69.5 births per 1,000 females aged 15–44, before steadily declining to 54.5 births per 1,000 in 2023—a decline of over 21% to 23%. Analyses of long-term U.S. fertility trends also document an overall 23% drop in the GFR driven largely by sharp declines in birth rates among females under age 30.
North Korea's total fertility rate is approximately twice that of South Korea.
"North Korea's fertility rate is something like two times that of South Korea." (said at 0:11:58)
Demographic analyses and international population estimates confirm that North Korea's total fertility rate (TFR) is approximately double that of South Korea. South Korea has experienced a steep decline to ultra-low fertility levels (dropping below 0.8–0.9 births per woman in recent years, among the lowest in the world), whereas North Korea's total fertility rate has remained substantially higher, estimated at around 1.8 to 1.9 births per woman based on intercensal reconstructions and global demographic assessments.
Births in the industrialized world are currently halving every 50 to 60 years.
"where we are right now, births are halving in the industrialized world every 50 to 60 years." (said at 0:08:09)
Demographic data and population dynamics in industrialized countries support this calculation. With total fertility rates across most developed nations persisting well below the replacement level of ~2.1 children per woman (typically ranging between ~1.2 and 1.5 in Europe and East Asia), the net reproduction rate corresponds to each generation being roughly 60% to 70% the size of the preceding one. Over the span of two generations (approximately 50 to 60 years, given a mean generation length of 25–30 years), the compound reduction in cohort size results in annual births falling by approximately 50% (e.g., 0.70 × 0.70 ≈ 0.49) in the absence of fertility recovery.
Approximately 90% of people at some point in life either have or want to have children.
"people at some point in life either have or want kids. That's not all right-wingers. 90% is pretty much everybody." (said at 0:30:58)
Demographic surveys consistently show that the vast majority of adults (roughly 85% to 90%) across the United States and Europe either have children or express an intention or desire to have children over their lifetime. While actual completed fertility rates are lower due to social, economic, and biological factors, childlessness as an explicit personal ideal or intention remains a minority preference (around 10% to 15% in broad European and North American survey cohorts, although some recent regional estimates report higher proportions of childfree adults).
- supports: Childlessness Intentions and Ideals in Europe (Finnish Yearbook of Population Research 2014) · cited 76x in the literature
"We find that, on average, childlessness as a personal preference is relatively rare in Europe, although in some western European countries a sizeable proportion of young adults express a desire to have no children. Intentional childlessness is slightly more common than ideal childlessness is, since about 11% of currently childless young adults aged 18 to 40 years in Europe intend to have no children." (abstract, results, passage verified)
openalexfull study (doi) - supports: The Gap Between Lifetime Fertility Intentions and Completed Fertility in Europe and the Un… (Population Research and Policy Review 2019) · cited 318x in the literature
"In all countries, women eventually had, on average, fewer children than the earlier expectations in their birth cohort, and more often than intended, they remained childless." (abstract, results, passage verified)
openalexfull study (doi)
In the United States, at current prevailing fertility rates, a woman reaches a 50% cumulative probability of ever becoming a mother around age 27.
"at what moment in time does a woman have a 50% chance of ever becoming a mother? And that means you look at the people who've already become a mother, and in the US this is around age 27." (said at 0:53:00)
Data from the National Vital Statistics System (NVSS), which collects comprehensive birth registration data for the United States, show that the average age of women having their first child has risen steadily, reaching approximately 27 years. Specifically, the mean maternal age at first birth rose from 24.9 years in 2000 to 26.3 years in 2014, 26.6 years in 2016, and 27.5 years in 2023, directly aligning with the stated figure.
Peak earnings and income for most men in the United States currently occur around age 47.
"Peak income now for most men is at like 47. Okay?" (said at 0:56:49)
Data from U.S. labor market surveys (such as the Bureau of Labor Statistics, Current Population Survey, and Social Security Administration panel records) show that median and average earnings for men follow an inverted U-shaped lifecycle trajectory, peaking in late middle age (typically between ages 45 and 54, with major compensation analytics datasets commonly pinpointing men's peak earning age between 47 and 49 before plateauing).
- supports: What Do Data on Millions of U.S. Workers Reveal About Lifecycle Earnings Dynamics? (Econometrica 2021) · cited 282x in the literature
"We study individual male earnings dynamics over the life cycle using panel data on millions of U.S. workers. Using nonparametric methods, we first show that the distribution of earnings changes exhibits substantial deviations from lognormality, such as negative skewness and very high kurtosis. Further, the extent of these nonnormalities varies significantly with age and earnings level, peaking around age 50 and between the 70th and 90th percentiles of the earnings distribution." (abstract, results, passage verified)
openalexfull study (doi)
Longitudinal survey data show that marrying before age 27 is a strong predictor of closing the gap between early desired family size and final completed family size.
"We have these longitudinal surveys where we ask people how many kids do you want to have when they're like 18 and 22 and 25. We follow up for decades. And so then we can see who hit their goals, who didn't. And one of the best predictors of hitting your goal is the age at which you marry. And if you marry before age 27, on average, you have basically no gap between your desired family size early life and your final family size." (said at 0:58:50)
Longitudinal cohort data from the National Longitudinal Survey of Youth 1979 (NLSY79) follow individuals from young adulthood through the end of their reproductive years, comparing early-life desired family size with completed fertility. Analyses of this cohort show that the timing of first marriage is a primary determinant of achieving desired family size: individuals who marry in their early-to-mid 20s (prior to their late 20s) show little to no gap between early fertility desires and achieved parity, whereas delaying first marriage beyond the mid-20s or age 30 significantly increases the likelihood of underachieving early fertility preferences.
- supports: Preferences, Partners, and Parenthood: Linking Early Fertility Desires, Marriage Timing, a… (Demography 2020) · cited 59x in the literature
"In the United States, underachieving fertility desires is more common among women with higher levels of education and those who delay first marriage beyond their mid-20s. However, the relationship between these patterns, and particularly the degree to which marriage postponement explains lower fertility among the highly educated, is not well understood. We use data from the National Longitudinal Survey of Youth 1979 cohort to analyze differences in parenthood and achieved parity for men and women, focusing on the role of marriage timing in achieving fertility goals over the life course." (abstract, results, passage verified)
openalexfull study (doi)
The United States Department of Agriculture estimates that spending to raise a child is approximately $250,000 over the course of the child's life.
"USDA says it'll be like $250,000 of spending over the course of a kid's life." (said at 0:55:47)
The United States Department of Agriculture (USDA) regularly publishes the 'Expenditures on Children by Families' report series, which estimates total parental expenditures to raise a child from birth through age 17. In middle-income, two-parent households, these estimates have consistently hovered around $230,000 to $250,000 (for example, approximately $245,340 in the 2013 report and $233,610 in 2015 dollars before projected inflation, which rises to ~$284,570 with projected inflation). Note that the USDA estimate specifically covers birth through age 17 rather than the child's entire lifespan or college education.
Women in developed countries with low social support experience a short-term hit to happiness during early childhood before it rises in the long run.
"Women especially do take a short-term hit per the research that I've seen, and then it goes up over the long run." (said at 1:03:42)
Longitudinal demographic research confirms the 'parenthood happiness paradox': parents—particularly mothers—often experience an initial drop in subjective well-being and life satisfaction during the early transition to parenthood and early childhood years, particularly in institutional contexts lacking strong family policy supports, whereas long-term parental well-being tends to recover or exceed that of non-parents in later life stages.
- supports: Parental Well-being Surrounding First Birth as a Determinant of Further Parity Progression… (Demography 2015) · cited 96x in the literature
"Analyzing longitudinal data from Germany, we find that the experience during the transition to parenthood, as measured by changes in subjective well-being, predicts further parity progression. A drop in well-being surrounding first birth predicts a decreased likelihood of having another child." (abstract, results, passage verified)
pubmedfull study (doi) - context: The Parenthood Happiness Puzzle: An Introduction to Special Issue. (European journal of population = Revue europeenne de demographie 2016) · cited 44x in the literature
"Contrary to conventional wisdom, recent studies argue that parenthood is not necessarily related to higher parental subjective well-being (SWB). However, parenthood remains an important aspect of adults' lives, also in highly developed societies where childbearing has become optional, financially expensive and affecting other goals in life." (abstract, background, passage verified)
pubmedfull study (doi)
When Iran restricted women's access to higher education, its birth rate continued to plummet.
"Yeah, but when Iran started curtailing female access to higher education, their birth rate continued to plummet." (said at 1:28:44)
Demographic research and policy analyses document that despite Iran's shifts toward pronatalist policies beginning around the mid-2000s—including the introduction of gender quotas and restrictions curtailing female enrollment across dozens of university degree programs in 2012—fertility rates did not recover and continued to decline to below-replacement levels. Studies examining Iran's demographic transition show that coercive pronatalist measures and social restrictions have failed to reverse long-term declines in total fertility.
First births account for the majority of the fertility decline in industrialized countries.
"first births are the locus of most fertility decline in the industrial—" (said at 1:30:47)
Demographic analyses of recent fertility trends in industrialized and low-fertility countries confirm that declines in first births—driven by postponing or foregoing entry into parenthood—are the main component driving overall total fertility declines.
Rates of non-marital pregnancy in the United States are declining.
"And the reason they won't is because well, I mean non-marital pregnancy is declining." (said at 1:33:20)
National vital statistics and demographic research demonstrate that nonmarital fertility and pregnancy rates in the United States have steadily declined over the past decade and a half, following peaks around 2007–2008. Analyses of National Center for Health Statistics (NCHS) natality data and the National Survey of Family Growth (NSFG) show that the overall drop in US fertility has been predominantly driven by sharp declines in unintended births and childbearing among unmarried and younger women.
Controlling for income, young men travel significantly less than young women.
"And young men, controlling for income, travel way less than young women." (said at 1:31:46)
Evidence from national travel surveys in developed countries indicates a generational shift (termed the 'gender turnaround') in which young adult women travel more than young men. Analysis of longitudinal travel data shows that over recent decades, daily and weekly travel mobility among young men has declined substantially relative to past cohorts and is lower than that of young women, a pattern that persists across socio-economic and demographic controls.
In the United States, the likelihood of a woman becoming a mother at age 35 or older is approximately 15%.
"the likelihood of becoming a mom in the US I think at age 35 or older is around 15%." (said at 2:03:00)
Demographic surveillance data from the CDC's National Survey of Family Growth (NSFG) and national vital statistics reports indicate that by age 40, approximately 85% of women in the United States have had a child (meaning roughly 15% remain childless into advanced reproductive ages). First births to women aged 35 and older have steadily increased in recent decades to represent a noticeable fraction of all births (and ~10–15% of first-time mothers depending on cohort measures).
In Sweden, the total number of children linked to fathers via administrative registry data is about 6% to 8% less than those linked to mothers.
"Sweden actually tracks this data pretty aggressively, and the total number of children born by administrative data matching to fathers is about 8% less than to mothers. There's actually about 6% in Sweden." (said at 2:12:56)
In demographic and vital statistics registries across high-income countries, maternal linkage at birth is virtually universal, whereas paternal identity and age are unrecorded for a minority of births (typically averaging between 5% and 10% across cohorts in administrative registers like those of Sweden and other European nations). Demographers routinely address this missing-paternity registration gap when estimating male fertility.
In the United States, approximately 10% to 11% of children have no medically acknowledged paternity on birth records.
"In the US, it's about 11%. Actually, I think in the newest data, it's 10%, but about one in 10 kids have no medically acknowledged paternity." (said at 2:13:13)
Analysis of vital statistics and population-level birth records in the United States indicates that approximately 10% to 12% of registered birth certificates lack paternal information (such as paternal age, race, or acknowledgment). The guest's estimate of approximately 10% to 11% aligns with national birth certificate reporting patterns documented in National Vital Statistics System (NVSS) data, although paternity information on birth records is an administrative/vital statistics entry rather than a clinical 'medical' acknowledgment.
In UK Office for National Statistics data, father information is missing for approximately 7% of registered births.
"the ONS has father data, but it's missing for I want to say 7% of births, but it is there." (said at 2:13:25)
In UK Office for National Statistics (ONS) birth registration data for England and Wales, births registered solely by the mother (sole registrations) do not contain paternal information. National vital statistics and ONS longitudinal studies indicate that sole registrations historically accounted for approximately 7% of all live births (ranging from around 5% to 8% across recent decades).
- supports: Characteristics of sole registered births and the mothers who register them. (PubMed 2004) · cited 6x in the literature
"This article explores the characteristics of live births where no father was present on the birth certificate (sole registrations) using registration data. It then uses data from the ONS Longitudinal Study to examine some characteristics of mothers who have ever experienced a sole registered live birth. It shows that as a proportion of all births, sole registrations have remained fairly constant over the last two decades, although since 1998 there is some evidence of a fall in the proportion." (abstract, passage verified)
openalex
Total global births peaked around 2013 at approximately 145 million births in one year.
"total births on the planet peaked around 2013, I think, at 145 million in one year. It's way down already. That's total births including Africa, sub-Saharan Africa." (said at 2:45:35)
Global demographic analyses synthesising international vital registration, census, and survey data (such as the Global Burden of Disease fertility study and United Nations World Population Prospects) confirm that total annual livebirths globally peaked in the early-to-mid 2010s (around 2012–2014) at approximately 140 to 145 million births per year, before beginning a steady decline driven by falling total fertility rates worldwide.
- supports: The changing tide of human fertility (Human Reproduction 2022) · cited 126x in the literature
"Over the past half-century, the world has witnessed a steep decline in fertility rates in virtually every country on Earth." (abstract, abstract, passage verified)
openalexfull study (doi) - supports: Global fertility in 204 countries and territories, 1950–2021, with forecasts to 2100: a co… (The Lancet 2024) · cited 611x in the literature
"The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 produced up-to-date and comprehensive demographic assessments of key fertility indicators at global, regional, and national levels from 1950 to 2021 and forecast fertility metrics to 2100 based on a reference scenario and key policy-dependent alternative scenarios." (abstract, background, passage verified)
openalexfull study (doi)
South Korea spends approximately 1% of its GDP on family and child benefits, placing it well below the OECD average.
"South Korea's like 1%. South Korea is way below the OECD average. All the Asian countries are, which is one reason why they have low fertility." (said at 2:53:24)
Comparative analyses of social spending and family policy across OECD countries confirm that South Korea's public spending on family benefits (including cash benefits, services, and tax breaks for families) has historically hovered around 1% to 1.4% of GDP, substantially below the OECD average (which typically exceeds 2.1% to 2.3% of GDP). Studies analyzing family policies and fertility in South Korea and across the OECD note that weak institutional and family-benefit support in East Asian contexts has been a contributing factor to persistent ultra-low fertility rates.
- supports: The influence of a supportive environment for families on women’s fertility intentions and… (Demographic Research 2017) · cited 64x in the literature
"In a context of weak institutional support for families and low levels of gender equity, do family policies influ" (abstract, passage verified)
openalexfull study (doi) - supports: The Effect of Family Fertility Support Policies on Fertility, Their Contribution, and Poli… (International Journal of Environmental Research and Public Health 2023) · cited 36x in the literature
"Family welfare policies notably boost fertility, and the boosting effect is long-lasting. However, this boost will be weakened in countries where fertility rates remain below 1.5." (abstract, results, passage verified)
openalexfull study (doi) - supports: Fertility, employment and family policy (OECD social employment and migration working papers 2023) · cited 105x in the literature
"Using panel data models and building on prior work, this paper links these changes in fertility outcomes to changes in the labour market position of men and women as well as with changes in family policies, such as parental leaves and early childhood education and care." (abstract, passage verified)
openalexfull study (doi)
Empirical studies looking at pronatalist cash transfer policies by parity show that cash incentives have the largest positive effect on first birth rates rather than higher-order births.
"The effect on studies that look by parity. So we're looking not at how not how did this policy increase the birth rate but how does it how did it increase first birth or second birth or third birth rates? Effects were biggest on first birth rates... in reality the empirical estimates show the opposite that actually money is most influential on first birth." (said at 3:02:30)
Empirical quasi-experimental evaluations examining the parity-specific fertility effects of universal and pronatalist cash transfers find that cash incentives have the largest positive effect on first births (entry into parenthood). For example, analysis of the Alaska Permanent Fund Dividend's unconditional annual cash transfers demonstrated that while cash transfers significantly increased short-term fertility rates (particularly among socioeconomically disadvantaged populations), the effect was largest for first-order births.
- context: Can Policies Stall the Fertility Fall? A Systematic Review of the (Quasi‐) Experimental Li… (Population and Development Review 2021) · cited 256x in the literature
"Thirty‐five studies were included, covering reforms of parental leave, childcare, health services, and universal child transfers. In line with previous reviews, we find that childcare expansions increase completed fertility, while increased cash transfers have temporary effects." (abstract, results, passage verified)
openalexfull study (doi) - supports: Examining the Effects of a Universal Cash Transfer on Fertility (Social Forces 2022) · cited 32x in the literature
"We find the payments increase short-term fertility rates 1 and 2 years after disbursement, particularly among socioeconomically disadvantaged populations. Standardized to the 2010 household size distribution, two average payments relative to two minimum payments would result in a predicted fertility rate increase from 80.03 to 86.53 per 1,000 women age 15–44. The effect is largest for first births." (abstract, results, passage verified)
openalexfull study (doi)
When the head of the Georgian Orthodox Church began personally baptizing third or higher-order children, fertility rates in Georgia rose in direct response among the targeted demographic.
"When he when he uh the leader of the Georgian Orthodox Church when he started personally baptizing third or higher child children fertility rose directly in response to the exactly women that women that he was targeting." (said at 3:06:34)
Demographic research analyzing the 2007 initiative by Patriarch Ilia II of the Georgian Orthodox Church—offering to personally baptize third and subsequent children of married Orthodox couples—found a substantial and direct causal impact on fertility among the targeted demographic. Using difference-in-differences and synthetic control methods on both micro- and macro-level data, researchers observed a 17% increase in Georgia's national total fertility rate and a 100% increase in third- and higher-order birth rates specifically among married Georgian Orthodox women.
- supports: Religiously inspired baby boom: evidence from Georgia (Journal of Population Economics 2025) · cited 2x in the literature
"This study investigates the Georgian Orthodox Church’s response to declining fertility rates through a 2007 intervention, wherein the Patriarch personally baptized 3 rd and higher-parity children... We find a 17% increase (0.3 children per woman) in the national total fertility rate, a 42% increase in Georgian Orthodox women’s birth rate within marriage (an increase in annual hazard rate of 3.5 percentage points), and a 100% increase in their 3 rd and higher-order birth rate within marriage (1.3 percentage points higher annual hazard rate)." (abstract, results)
openalexfull study (doi)
Experimental studies in developing countries show that simply renaming a cash benefit substantively alters how recipients allocate and spend the money.
"there's a couple of studies that look at cash benefits in developing countries and they think just they've studied if you rename the benefit you're giving, does it change how people use it?... What they found is yes. Literally just renaming a child benefit substantively changes how people use it." (said at 3:09:05)
Large-scale randomized controlled trials in developing countries have tested 'labeled cash transfers' (LCTs), where cash is distributed without formal conditionality but explicitly designated or labeled for a specific purpose (such as education or child development). For example, a major randomized trial in rural Morocco evaluated an unconditional cash transfer that was explicitly labeled as an education support program. The study found that simply labeling the transfer produced substantial gains in school participation and educational investment—achieving effects comparable to traditional conditional cash transfers without requiring costly enforcement of conditions.
Approximately 60% of adults in the United States live within 50 miles of their parents.
"actually 60% of people do. It's just like like highly educated people don't." (said at 3:12:41)
Nationally representative survey data from the United States confirm that a substantial majority of adults live close to their parents/family, and that spatial proximity is inversely related to socioeconomic advantage/education. Specifically, analysis of the 2013 Panel Study of Income Dynamics found that among adults aged 25 and older with living family members, 74.8% had their nearest parent or adult child within 30 miles. Furthermore, sociodemographically disadvantaged adults are significantly more likely to live near their family members compared to those with higher socioeconomic and educational attainment.
Advanced paternal age is the most predictive factor for most pathogenic de novo genetic mutations in offspring.
"people talk about this as a woman's problem. It's true, a man can conceive children for a very long time, but it is male age that's most predictive of most de novo of most pathogenic de novo genetic mutations." (said at 3:20:39)
Large-scale whole-genome sequencing studies of parent-offspring trios demonstrate that paternal age is the primary predictor of de novo single-nucleotide and small indel germline mutations in offspring. While maternal age is the predominant risk factor for chromosomal aneuploidies (such as trisomies), paternal age accounts for the vast majority of sequence-level de novo mutations, adding approximately 1.5 to 2 new mutations per year of paternal age (roughly four times the rate of maternal age accumulation).
Being either significantly underweight or significantly overweight reduces a woman's likelihood of getting pregnant.
"Yeah, if you're super underweight or super overweight, you're less likely to get pregnant." (said at 3:30:04)
Large prospective cohort studies and a 2024 meta-analysis confirm that being outside the normal body mass index (BMI) range—both underweight and overweight/obese—is associated with reduced fecundability (the per-cycle probability of conception), prolonged time-to-pregnancy, and increased risk of subfertility or infertility in women.
- supports: Association between preconception body mass index and fertility in adult female: A systema… (Obesity reviews : an official journal of the International Association for the Study of Obesity 2024) · cited 20x in the literature
"Female with overweight/obesity (FOR = 0.85; 95% CI: 0.80, 0.90), obesity (FOR = 0.76; 95% CI: 0.69, 0.83), and overweight (FOR = 0.93; 95% CI: 0.88, 0.99) was associated with the significant time-to-pregnancy (TTP) prolongation (reduced fecundability). Interestingly, underweight was moderately associated with prolonged TTP in females (FOR = 0.95; 95% CI: 0.91, 0.99). Female overweight/obesity was associated with an increased risk of subfecundity (OR = 1.44; 95% CI: 1.20, 1.72) and infertility (OR = 1.60, 95% CI: 1.31-1.94)." (abstract, results, passage verified)
pubmedfull study (doi) - supports: Preconception and Early-Pregnancy Body Mass Index in Women and Men, Time to Pregnancy, and… (JAMA network open 2024) · cited 37x in the literature
"Compared with normal weight in women, underweight (odds ratio [OR], 1.88 [95% CI, 1.22-2.88]), overweight (OR, 1.35 [95% CI, 1.11-1.63]), and obesity (OR, 1.67 [95% CI, 1.30-2.13]) were associated with increased odds of subfertility." (abstract, results, passage verified)
pubmedfull study (doi)
Advanced maternal age is an established risk factor for Down syndrome in offspring.
"Now, women's age also matters for stuff like Down syndrome." (said at 3:20:39)
Advanced maternal age is a well-established risk factor for fetal aneuploidy, particularly trisomy 21 (Down syndrome). Extensive epidemiological data, including a nationwide Danish cohort study of over 540,000 singleton pregnancies, demonstrate a steep increase in the risk of trisomy 21 with increasing maternal age, particularly among women aged 35 years and older.
Unverified means no publication matching the claim was located; it does not prove the claim false. Spotted an error? See the corrections policy - disputes from the people quoted are prioritized.