Offspring
Martha Bailey & William Collins
American Economic Journal: Macroeconomics, April 2011, Pages 189-217
Abstract:
We examine the hypothesis that advances in household technology caused the US baby boom, and we find no support for this claim. Advances in household technology occurred before the baby boom, while fertility declined. From 1940 to 1960, levels/changes in county-level appliance ownership and electrification negatively predict levels/changes in fertility rates. Exposure to electricity in early adulthood and children-ever-born are negatively correlated for the relevant cohorts. The Amish, who used modern technologies much less than other US households, experienced a coincident baby boom. This evidence can be reconciled with economic theory if other home-produced goods are substitutes with children.
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Fathers' time investments in children: Do sons get more?
Kristin Mammen
Journal of Population Economics, July 2011, Pages 839-871
Abstract:
This paper uses the 2003 American Time Use Survey to examine the effects of child gender on paternal time with children in married two-parent families. The results show that fathers of boys invest more time in children than those with only daughters and reduce their leisure time without children to do so. Boys get more of this time than girls in all-girl families and compared to their own sisters. Girls with brothers receive more of fathers' time than girls with only sisters, but this is primarily in television watching, so whether this advantages them is open to question.
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Isaac Galatzer-Levy et al.
Journal of Family Psychology, forthcoming
Abstract:
A recent article in New York Magazine echoed what psychological studies of parenthood have consistently demonstrated since the 1970s: "Most people assume that having children will make them happier. Yet a wide variety of academic research shows that parents are not happier than their childless peers, and in many cases are less so" (Senior, 2010). There is consistent evidence that, as opposed to other life events that cause transient disruptions in life satisfaction, becoming a parent appears to cause harm to individual subjective well-being (Twenge, Campbell, & Foster, 2003), and that this harm is sustained over time (Clark, Diener, Georgellis, & Lucas, 2008). The current investigation was predicated on the concern that these findings may be the result of the methodology used to examine them. As the experience of parenthood does not represent a unified phenomenon, we employed a methodological approach that allows for the exploration of heterogeneity as well as its predictors. By modeling heterogeneous trajectories within a prospective design from 4 years prior to 4 years after the birth of a parent's first child, we find that the majority of individuals (84.2%) demonstrate no long-term effects on life satisfaction in response to childbirth. Only a small percentage demonstrate the sustained declines (7.2%), and a significant cohort, previously unobserved in the literature, demonstrate dramatic and sustained improvements in response to parenthood (4.3%), providing compelling evidence for heterogeneity in life satisfaction among parents. Key demographic covariates that distinguish between trajectories of response are also explored.
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Wealth, status, and fitness: A historical study of Norwegians in variable environments
Gine Roll Skjærvø et al.
Evolution and Human Behavior, forthcoming
Abstract:
Wealth and status covary with lifetime reproductive success in preindustrial human populations. Local ecology is likely to modify this association, but details of this presumed relationship are not yet known. We sought to determine whether local ecology modifies the relationship between status and fitness (number of grandchildren). Our approach to the problem was to measure variation in fitness relative to status (landless or with land) and to local ecology (inland versus coastal communities). We also analyzed life history traits that might explain observed variations in fitness. Our results confirm previous findings that both status (landless=9.9 vs. with land=16.5) and ecology (inland=12.3 vs. coast=14.1) affect the number of grandchildren produced by a female in pre-industrial society. We also found that the differences in number of children between the status groups were less pronounced on the coast (landless=12.0 vs. with land=16.1) than inland (landless=7.8 vs. with land=16.8). Our findings are novel because they suggest that the fitness consequences of human status may depend on details of local ecology. We discuss four different mechanisms that could account for these fitness differences: (1) differential reproductive rate of mothers, (2) differential marriage rate of children (3) differential survival rate of children, and (4) different social practices (breastfeeding, inheritance of property and diet).
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Month of Conception and Risk of Autism
Ousseny Zerbo et al.
Epidemiology, forthcoming
Background: Studies of season of birth or season of conception can provide clues about etiology. We investigated whether certain months or seasons of conception are associated with increased risk of autism spectrum disorders, for which etiology is particularly obscure.
Methods: The study population comprises 6,604,975 children born from 1990 to 2002 in California. Autism cases (n = 19,238) were identified from 1990 through 2008 in databases of the California Department of Developmental Services, which coordinates services for people with developmental disorders. The outcome in this analysis was autism diagnosed before the child's sixth birth date. The main independent variables were month of conception and season of conception (winter, spring, summer, and fall). Multivariate logistic regression models were used to estimate odds ratios (ORs) with their 95% confidence intervals (CIs) for autism by month of conception.
Results: Children conceived in December (OR = 1.09 [95% CI = 1.02-1.17]), January (1.08 [1.00-1.17]), February (1.12 [1.04-1.20]), or March (1.16 [1.08-1.24]) had higher risk of developing autism compared with those conceived in July. Conception in the winter season (December, January, and February) was associated with a 6% (OR = 1.06, 95% CI = 1.02-1.10) increased risk compared with summer.
Conclusions: Higher risks for autism among those conceived in winter months suggest the presence of environmental causes of autism that vary by season.
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Consequences of Parental Divorce for Child Development
Hyun Sik Kim
American Sociological Review, forthcoming
Abstract:
In this article, I propose a three-stage estimation model to examine the effect of parental divorce on the development of children's cognitive skills and noncognitive traits. Using a framework that includes pre-, in-, and post-divorce time periods, I disentangle the complex factors affecting children of divorce. I use the Early Childhood Longitudinal Study-Kindergarten Class 1998 to 1999 (ECLS-K), a multiwave longitudinal dataset, to assess the three-stage model. To evaluate the parameters of interest more rigorously, I employ a stage-specific ordinary least squares (OLS) model, a counterfactual matching estimator, and a piece-wise growth curve model. Within some combinations of developmental domains and stages, in particular from the in-divorce stage onward, I find negative effects of divorce even after accounting for selection factors that influence children's skills and traits at or before the beginning of the dissolution process. These negative outcomes do not appear to intensify or abate in the ensuing study period.
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Susan Golombok et al.
Journal of Family Psychology, April 2011, Pages 230-239
Abstract:
An increasing number of babies are being born using donated sperm, where the child lacks a genetic link to the father, or donated eggs, where the child lacks a genetic link to the mother. This study examined the impact of telling children about their donor conception on mother-child relationships and children's psychological adjustment. Assessments of maternal positivity, maternal negativity, mother-child interaction, and child adjustment were administered to 32 egg donation, 36 donor insemination, and 54 natural conception families with a 7-year-old child. Although no differences were found for maternal negativity or child adjustment, mothers in nondisclosing gamete donation families showed less positive interaction than mothers in natural conception families, suggesting that families may benefit from openness about the child's genetic origins.
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Sibling composition and selective gender-based survival bias
Rubiana Chamarbagwala
Journal of Population Economics, July 2011, Pages 935-955
Abstract:
We examine the relationship between the gender composition of surviving older siblings and gender differences in children's survival using data from the Third National Family and Health Survey (2005-2006) in India. We address the possibility of unobserved mother-specific heterogeneity and explore the role of household wealth, parental education, and urban residence in strengthening or weakening selective gender-based survival bias. We find that daughters' survival disadvantage increases in the number of older sisters and decreases in the number of older brothers they have. The opposite is true for sons' survival disadvantage. Household wealth, parental education, and urban residence are all found to intensify selective survival bias among daughters and sons.
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Contributions to College Costs by Married, Divorced, and Remarried Parents
Ruth López Turley & Matthew Desmond
Journal of Family Issues, June 2011, Pages 767-790
Abstract:
Using parent interview data from a subsample of the National Postsecondary Student Aid Study (NPSAS), the authors compared the financial contributions of married, divorced, and remarried parents toward their children's college education and found that although divorced parents contributed significantly less than married parents, remarried parents contributed amounts similar to those of divorced parents, despite having incomes similar to those of married parents. The authors also investigated the financial contributions of divorced and remarried parents who lived in states that permit courts to extend child support beyond the age of 18 for college expenses (postmajority states) and found that living in a postmajority state is not associated with increased parent contributions.
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A Global Perspective on Happiness and Fertility
Rachel Margolis & Mikko Myrskylä
Population and Development Review, March 2011, Pages 29-56
Abstract:
The literature on fertility and happiness has neglected comparative analysis. We investigate the fertility/happiness association using data from the world values Surveys for 86 countries. We find that, globally, happiness decreases with the number of children. This association, however, is strongly modifed by individual and contextual factors. Most importantly, we find that the association between happiness and fertility evolves from negative to neutral to positive above age 40, and is strongest among those who are likely to beneft most from upward intergenerational transfers. In addition, analyses by welfare regime show that the negative fertility/happiness association for younger adults is weakest in countries with high public support for families, and the positive association above age 40 is strongest in countries where old-age support depends mostly on the family. Overall these results suggest that children are a long-term investment in well-being, and highlight the importance of the life-cycle stage and contextual factors in explaining the happiness/fertility association.
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Valuing Mother And Child Health: The Intrauterine Environment
Stefanos Nastis & Thomas Crocker
Economics & Human Biology, forthcoming
Abstract:
The paper estimates the value a mother assigns to own health relative to child health. Estimation of relative health valuation requires the decomposition of a child health improvement into its direct effect on the child's health and its indirect effect, through improvements in maternal health. Failure to distinguish the impact of the direct and indirect effects can lead to biased estimates. We consider the intrauterine environment of a pregnant mother and her unborn child, where maternal health inputs are choice variables and her health affects child health. The empirical estimates suggest that mothers value child health up to six times higher than own health, and that the relative value depends on maternal consumption patterns and household characteristics.
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Sex Selection and Gender Balance
V. Bhaskar
American Economic Journal: Microeconomics, February 2011, Pages 214-244
Abstract:
We model the equilibrium sex ratio when parents can choose the sex of their child. With intrinsic son preference, sex selection results in a male-biased sex ratio. This is inefficient due to a marriage market congestion externality. Medical innovations that facilitate selection aggravate the inefficiency. If son preference arises endogenously, due to population growth causing an excess supply of women on the marriage market, selection may improve welfare. Empirically, sex selection causes an excess of males and reduces welfare in China. In most parts of India, cohort sizes are growing, implying an excess supply of women.
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Kateřina Hollá et al.
Journal of Sexual Medicine, April 2011, Pages 1083-1091
Introduction: This article presents the results of representative national studies comparing the behavior and attitudes of Czech and Romanian women regarding abortion and contraception use.
Aim: Describe the attitudes to abortion and incidence of abortion in female population of these countries.
Methods: Independently and anonymously conducted questionnaire with 1,011 Czech and 1,001 Romanian women, with the participants' age from 15 to 50 years. The sample represented both Czech and Romanian female populations with respect to age, education, and the size of their place of residence.
Main Outcome Measures: Questionnaire studies awareness, attitudes, and behavior related to the area of sexual life, contraception, and family planning.
Results: Based on the acquired information, it can be postulated that Romanian women, despite having a less liberal opinion on abortions than their Czech peers, undergo abortion more often than Czech women (Romanian 28%, Czech 16%), are less informed about potential side effects, and more often use less reliable methods of contraception (the so-called "natural contraception"-vs. hormonal contraception, which is the method of choice of Czech women).
Conclusion: These results indicate that despite more liberal attitudes toward abortion, Czech women have less frequent incidence of abortion than Romanian women and they have more relevant information about contraception and their sexual behavior is more conscious and responsible.
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Marie-Jo Brion et al.
International Journal of Epidemiology, forthcoming
Background: A novel approach is explored for improving causal inference in observational studies by comparing cohorts from high-income with low- or middle-income countries (LMIC), where confounding structures differ. This is applied to assessing causal effects of breastfeeding on child blood pressure (BP), body mass index (BMI) and intelligence quotient (IQ).
Methods: Standardized approaches for assessing the confounding structure of breastfeeding by socio-economic position were applied to the British Avon Longitudinal Study of Parents and Children (ALSPAC) (N 5000) and Brazilian Pelotas 1993 cohorts (N 1000). This was used to improve causal inference regarding associations of breastfeeding with child BP, BMI and IQ. Analyses were extended to include results from a meta-analysis of five LMICs (N 10 000) and compared with a randomized trial of breastfeeding promotion.
Findings: Although higher socio-economic position was strongly associated with breastfeeding in ALSPAC, there was little such patterning in Pelotas. In ALSPAC, breastfeeding was associated with lower BP, lower BMI and higher IQ, adjusted for confounders, but in the directions expected if due to socioeconomic patterning. In contrast, in Pelotas, breastfeeding was not strongly associated with BP or BMI but was associated with higher IQ. Differences in associations observed between ALSPAC and the LMIC meta-analysis were in line with those observed between ALSPAC and Pelotas, but with robust evidence of heterogeneity detected between ALSPAC and the LMIC meta-analysis associations. Trial data supported the conclusions inferred by the cross-cohort comparisons, which provided evidence for causal effects on IQ but not for BP or BMI.
Conclusion: While reported associations of breastfeeding with child BP and BMI are likely to reflect residual confounding, breastfeeding may have causal effects on IQ. Comparing associations between populations with differing confounding structures can be used to improve causal inference in observational studies.
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Prenatal Stress and Risk of Infectious Diseases in Offspring
Nete Munk Nielsen et al.
American Journal of Epidemiology, 1 May 2011, Pages 990-997
Abstract:
Animal studies have suggested that prenatal stress could affect the immune system of the offspring. In a nation-wide cohort of all Danish children born from 1977 to 2004, the authors examined the association between prenatal stress, defined as maternal exposure to a stressful life event during pregnancy or in the 3-year period before conception, and the risk of severe or less severe infectious disease hospitalization in childhood. Log-linear Poisson regression models provided estimates of rate ratios. Compared with nonexposed children, children exposed prenatally to stress had a 25% (rate ratio (RR) = 1.25, 95% confidence interval (CI): 1.06, 1.47) and a 31% (RR = 1.31, 95% CI: 1.27, 1.35) increased risk of being hospitalized with a severe or a less severe infectious disease, respectively. Children born to mothers exposed to a stressful life event during pregnancy, during the 11 months before, or during the 12-35 months before conception were at 71% (RR = 1.71, 95% CI: 1.20, 2.45), 42% (RR = 1.42, 95% CI: 1.13, 1.78), and no increased (RR = 0.86, 95% CI: 0.63, 1.18) risk of severe infectious disease hospitalization. No obvious association between risk of less severe infectious disease hospitalization and timing of maternal exposure was observed. Although the authors could not determine whether this is a biologic effect of prenatal stress or an effect of other factors related indirectly to a stressful life event, their results add new information about the consequences of prenatal stress.
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Norman Li et al.
Social Indicators Research, May 2011, Pages 391-404
Abstract:
We examined factors related to attitudes toward marriage and the importance of having children in both the US and Singapore. Path analysis indicated that life dissatisfaction leads to materialism, and both of these factors lead to favorable attitudes toward marriage, which leads to greater desire for children. Further analysis indicated this model was effective in explaining the difference in desire for children between Singaporeans and Americans, whereby Singaporeans have lower life satisfaction, higher materialism, and lower attitudes toward marriage and children. Materialistic standards of success were also related to the emphasis women placed on potential marriage partners' earning capacity. As Singaporean women had higher materialistic standards, they also placed higher emphasis on potential mates' earning capacity. Results suggest a consideration of psychological variables such as life satisfaction, materialism, and mate preferences may lead to a better understanding of larger-scale socioeconomic issues, including low fertility rates among developed East Asian countries.
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Early-life conditions and age at first pregnancy in British women
Daniel Nettle, David Coall & Thomas Dickins
Proceedings of the Royal Society: Biological Sciences, 7 June 2011, Pages 1721-1727
Abstract:
There is growing evidence that the reproductive schedules of female mammals can be affected by conditions experienced during early development, with low parental investment leading to accelerated life-history strategies in the offspring. In humans, the relationships between early-life conditions and timing of puberty are well studied, but much less attention has been paid to reproductive behaviour. Here, we investigate associations between early-life conditions and age at first pregnancy (AFP) in a large, longitudinally studied cohort of British women (n = 4553). Low birthweight for gestational age, short duration of breastfeeding, separation from mother in childhood, frequent family residential moves and lack of paternal involvement are all independently associated with earlier first pregnancy. Apart from that of birthweight, the effects are robust to adjustment for family socioeconomic position (SEP) and the cohort member's mother's age at her birth. The association between childhood SEP and AFP is partially mediated by early-life conditions, and the association between early-life conditions and AFP is partially mediated by emotional and behavioural problems in childhood. The overall relationship between early-life adversities and AFP appears to be approximately additive.
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Lisa Berlin, Karen Appleyard & Kenneth Dodge
Child Development, January/February 2011, Pages 162-176
Abstract:
In the interest of improving child maltreatment prevention, this prospective, longitudinal, community-based study of 499 mothers and their infants examined (a) direct associations between mothers' experiences of childhood maltreatment and their offspring's maltreatment, and (b) mothers' mental health problems, social isolation, and social information processing patterns (hostile attributions and aggressive response biases) as mediators of these associations. Mothers' childhood physical abuse -- but not neglect -- directly predicted offspring victimization. This association was mediated by mothers' social isolation and aggressive response biases. Findings are discussed in terms of specific implications for child maltreatment prevention.
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Durable effects of implementation intentions: Reduced rates of confirmed pregnancy at 2 years
Jilly Martin et al.
Health Psychology, May 2011, Pages 368-373
Objective: To assess the long-term impact of implementation intention formation in reducing consultations for emergency contraception and pregnancy testing among teenage women.
Design: Teenage women visiting a family planning clinic were randomly assigned to implementation intention versus control conditions.
Main outcome measures: Objective measures of consultation outcomes were obtained from clinic records at 2-year follow-up (N = 227).
Results: Rates of consultation for emergency contraception and pregnancy testing in the implementation intentions condition were 19% and 33% lower, respectively, compared to the rates observed in the control condition. Pregnancy rates were 43% lower. Intervention participants who consulted for emergency contraception and pregnancy testing at baseline were more than twice as likely to change to consulting for contraceptive supplies over the follow-up period compared to equivalent control participants (19% vs. 9%).
Conclusion: The impact of implementation intention formation on reducing pregnancy risk among teenagers is durable over 2 years. Implementation intentions were successful in changing behavior among precisely those participants who were at greatest risk of becoming pregnant.
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Low-Income Fathers' Influence on Children
Marcia Carlson & Katherine Magnuson
ANNALS of the American Academy of Political and Social Science, May 2011, Pages 95-116
Abstract:
This article examines what we know about how low-income fathers matter for children. The authors first provide a theoretical background about how parents generally (and fathers more specifically) are expected to influence children's development and well-being. The authors note the importance of considering differences across children's age, gender, and race/ethnicity; and they identify key methodological challenges in this area. Then, they summarize the literature on residential fathers and child well-being, finding that greater involvement has been linked to better outcomes for children; however, much of this research has been conducted on more socioeconomically advantaged samples. For fathers who live away from their children, child support payments appear to improve children's outcomes, but the benefits of father-child interaction are much less clear and likely depend on the quality of the interaction and the characteristics of fathers. Overall, the authors conclude that low-income fathers can have a positive influence on children's well-being, but the evidence about the population overall is rather weak.
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Do Nonresidential Fathers' Financial Support and Contact Improve Children's Health?
Sandra Hofferth & Angela Pinzon
Journal of Family and Economic Issues, June 2011, Pages 280-295
Abstract:
Nonresidential father investment of time and money has been shown to ameliorate the negative consequences of family dissolution on children's behavior and achievement; however, no research has shown whether this investment also has positive effects on child health. Using data from the Early Childhood Longitudinal Survey, Kindergarten cohort, this research uses a two-wave cross-lagged model to examine how child support and contact are associated with maternal reports of children's physical health over time following parental separation. Child support in kindergarten is not associated with child health in third grade. Instead, children who are healthier in kindergarten receive greater financial support from their father. Although contact and child support are positively related, greater contact is not associated with better child health.
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Lisa Rosenthal & Marci Lobel
Social Science & Medicine, March 2011, Pages 977-983
Abstract:
The infant mortality rate for Black Americans in the US is more than twice the rate for White Americans, with similar racial disparities existing in rates of low birthweight and preterm delivery. Survivors of these adverse birth outcomes have poorer development and health in infancy, childhood, and adulthood. Increasingly, evidence suggests that maternal stress is an important risk factor for adverse birth outcomes. We offer a novel perspective on racial disparities in birth outcomes suggesting that Black American women are subject to unique sources of stress throughout their lives and particularly during pregnancy based on their multiple identities as women, Black, and pregnant. We draw on interdisciplinary work to examine three unique sources of stress for Black American women that elevate their risk for adverse birth outcomes: 1) abuses of Black American women by the medical system and issues of power in obstetrics that disadvantage Black American women; 2) contradictory societal pressures exerted on Black American women about whether they should have children; and 3) historical and contemporary stereotypes about Black American women related to sexuality and motherhood. We discuss implications of this analysis, including applications to research and intervention. Developing a better understanding of the experience of Black American women during pregnancy and throughout their lives offers insight into ways to reduce racial disparities in adverse birth outcomes and their lifelong consequences.
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What is driving the black-white difference in low birthweight in the US?
Aparna Lhila & Sharon Long
Health Economics, forthcoming
Abstract:
This is a first effort to quantify the contribution of different factors in explaining racial difference in low birthweight rate (LBW). Mother's health, child characteristics, prenatal care, socioeconomic status (SES), and the socioeconomic and healthcare environment of mother's community are important inputs into the birthweight production function, and a vast literature has delved into obtaining causal estimates of their effect on infant health. What is unknown is how much of the racial gap in LBW is explained by all these inputs together. We apply a nonlinear extension of the Oaxaca-Blinder method proposed by Fairlie to decompose this gap into the portion explained by differences in observed characteristics and the portion that remains unexplained. Data are obtained from several sources in order to capture as many observables as possible, although the primary data source is the Natality Detail Files. Results show that of the 6.8 percentage point racial gap in LBW, only 0.9-1.9 points are explained by white-black differences in endowments across those measures, and of those endowments, most of the gap in LBW is explained by the differences in SES. The unexplained difference is attributed to racial differences in the returns to or the marginal product of investments in infant health.
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William James
Journal of Biosocial Science, March 2011, Pages 167-184
Abstract:
This note categorizes the evidence for the hypothesis that mammalian offspring sex ratios (proportions male) are causally related to the hormone levels of both parents around the time of conception. Most of the evidence may be acknowledged to be correlational and observational. As such it might be suspected of having been selected; or of having been subject to other forms of bias or confounding; or, at any rate, of being inadequate as a firm basis for causal inference. However, there are other types of evidence that are not vulnerable to these types of criticism. These are from the following sources: (1) previously neglected data from Nazi Germany and Soviet Russia; (2) fulfilled predictions; (3) genetics; and (4) a network of logically (mathematically) related propositions, for some of which there is overwhelming empirical evidence. It is suggested that this variety of evidence confers greater overall credibility on the hypothesis than would be the case if all the evidence were of the same observational/correlational status. This observational/correlational evidence is tabulated to illustrate its consistency.
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Social monogamy and the threat of infanticide in larger mammals
Carola Borries, Tommaso Savini & Andreas Koenig
Behavioral Ecology and Sociobiology, April 2011, Pages 685-693
Abstract:
The evolution of social monogamy in larger mammals is difficult to explain because males usually do not invest much in direct offspring care and might achieve greater fitness by deserting a pregnant female to reproduce with additional females elsewhere. It has been hypothesized that socially monogamous males remain with the female year-round to protect their offspring from infanticide by new immigrant males. We investigated this idea by analyzing all cases of infant loss in a wild population of white-handed gibbons (Hylobates lar; Primates), in which most groups were socially monogamous and some polyandrous (137.5 group years). We examined the influence of (a) male intruder pressure on male immigration rates and (b) the presence of a new male in the group on infant loss. We found no relation between intruder pressure and male immigration rates. Infant loss was lowest (4.5%) for stable monogamy (probable father stayed from conception through infancy) and intermediate (25.0%; p = 0.166) for stable polyandry. If a new male immigrated after conception, however, the infant was lost in all cases (p < 0.01) independent of the presumed father's presence. Overall, 83.3% of infant losses were associated with the presence of a presumably unrelated male. Although the sample size is small, our results provide the first true support for the idea that the risk of infanticide is an important factor in the evolution of social monogamy in larger mammals.
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Andrew Francis
Journal of Population Economics, July 2011, Pages 813-837
Abstract:
In 1949, Mao Zedong and the People's Liberation Army defeated the Chinese Nationalist Army. Hundreds of thousands of mainland Chinese fled to the island of Taiwan. In this paper, I use the demographic consequences of the Chinese Communist Revolution and subsequent Taiwanese military policy to identify the effect of the marriage market sex ratio on women and children in Taiwan. I find that as the sex ratio rises, the bride price relative to the dowry increases, the fraction of female children in a family increases, the total number of children in a family decreases, and human capital investments in children increase.
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The sex ratio of offspring is associated with the mothers' age at menarche
Misao Fukuda et al.
Human Reproduction, June 2011, Pages 1551-1554
Background: Early menarcheal age is a risk factor for breast and ovarian cancers and is also associated with an increased spontaneous abortion rate. The aim of this study was to investigate whether there is a link between early menarcheal age and the offspring sex ratio.
Methods: We recorded the sex of 21208 live born infants, all singletons, born to 10 847 premenopausal women (mean attending age: 37.5 ± 7.2 years, range 22-54) who attended our clinics for obstetrical and gynaecological assessment. We calculated the sex ratio of newborn infants in relation to the mothers' age of menarche (from 9 to 18 years) and to the number of infants per woman (i.e. fertility index).
Results: A low offspring sex ratio (males/females) of 0.800 was observed in mothers who entered menarche at the age of 9 years; the odds ratio (OR) (95% confidence intervals) compared with those of control group with menarche at age 14 was 0.72 (0.29-1.79). The sex ratio remained low, until the group of mothers who entered menarche at 12 years of age [1.009; OR: 0.90 (0.85-0.95)]. The highest sex ratio was observed in mothers with a menarcheal age of 14 years (1.118; OR: 1.00 control) and it gradually decreased until the menarcheal age of 17 years [1.000; OR: 0.89 (0.15-5.26)]. The fertility index was also low in women with menarche at the age of 9 to 11 years.
Conclusions: Women entering menarche outside the normal range, especially those with earlier menarche, may have an increased chance of producing female offspring.