Fertility and patterns of labor force participation among married women

Abstract

Past research has shown that the labor market behavior of wives is discontinuous and affected by family events. Specifically, both cross‐sectional and panel data indicate that fertility decreases the period that a married woman spends working. Each birth appears to decrease labor force participation by one year or more. The present study attempts to specify these effects more completely. The variation in work patterns for each parity progression is examined to determine whether the fertility‐work effect is due to a few women who leave the labor force for an extended period during childbearing or due to a large number of women who have intermittent work histories. The analysis uses a national sample of women who were high school sophomores in 1955 and followed up as adults in 1970 and for whom retrospective data for each of the intervening years were obtained. Only married women with uncomplicated marital histories are included in the present study. We find dramatic evidence for two distinct types of response to childbearing. Women tend either to work almost continuously throughout the period or to drop out of the labor force for a very extended period of time after first birth.     

Changes in the timing of births in Melbourne, Australia

2 10-year marriage cohorts from 2 surveys of married women in Melbourne were compared on their timing of the 1st and 2nd births. The results showed that women who were married in the early 1970s were much more likely to delay their first birth until about the 3rd or 4th year of marriage compared with women who married in the 1960s. This tendency to delay the 1st birth was probably aided by effective contraception, as it coincided with widespread use of the oral contraceptive. There was no difference in the timing of the 2nd birth in relation th the 1st birth between the 2 marriage cohorts. Women who delayed childbearing also preferred smaller families. Indeed, the increase in the % of women delaying childbearing appears to be synonymous with the trend toward the two-child family. Altough the number of married women in the labor force increased significantly from the early to the later cohort, a desire to work was not usually cited as the reason for delaying childbearing. Rather, economic reasons were most frequently mentioned for delaying childbearing.     

Early sexual maturity among Pumé foragers of Venezuela: fitness implications of teen motherhood

Because humans have slow life histories, discussions of the optimal age at first birth have stressed the benefits of delayed reproduction. However, given the diversity of ecological, fertility, and mortality environments in which humans live, reproductive maturity is expected to be highly variable. This article uses reproductive histories to examine a pattern of early menarche and first birth among the Pume, a group of South American foragers. Age at menarche and first birth are constructed using both retrospective and cross‐sectional data for females over the age of 10 (n = 83). The objectives are first to define these patterns and then discuss their reproductive consequences. On average, Pume girls reach menarche at age 12.9, and give birth to their first child at age 15.3–15.5 (retrospective and cross‐sectional data, respectively). This populational average falls several years prior to what often is considered the human norm. Two questions are then considered. What are the infant mortality costs across a mother's reproductive career? How does surviving fertility vary with age at first birth? Results indicate that the youngest of first‐time mothers (<14) are four times more likely to loose their firstborns than older first‐time mothers (≥17). Given parity‐specific mortality rates, the optimal strategy to minimize infant mortality and maximize reproductive span is to initiate childbearing in the midteens. Women gain no additional advantage in surviving fertility by delaying childbearing until their late teens. Am J Phys Anthropol, 2008. © 2008 Wiley‐Liss, Inc.     

A delay in age at first mating results in the loss of future reproductive potential via apoptosis

Summary Women who delay childbearing risk subfertility. However, this loss of fertility is not a simple function of aging. Women who have had children early in life tend to maintain fertility longer, measured as a later age at menopause. But why should otherwise healthy women lose reproductive capacity? Loss of fertility independent of senescence, menopause, has been approached from two perspectives: evolution and development. Evolutionary biologists focus on how natural selection favors survival after reproductive ability has ceased, whereas reproductive biologists examine mechanisms by which women lose fertility with age and factors that influence the rate of reproductive aging. Combining mechanistic studies with evolutionary theory should allow us to define principles of the evolution of postembryonic development of ovaries, including the role of reproductive timing relative to sexual maturation. Achieving this will require identifying appropriate, and more experimentally tractable, taxa in which to study how early reproductive events influence lifetime fertility. We work with an invertebrate species, the cockroach Nauphoeta cinerea, with a complex reproductive biology in which females experience reproductive cycles, give live birth, and show age‐related decline in fertility. Thus, N. cinerea provides an opportunity to use an experimental approach to examine mechanisms by which females lose reproductive potential as they delay reproduction. Our results demonstrate that the loss of both oocytes ready for fertilization and future oocytes in females that delay mating is because of apoptosis. We suggest that loss of fertility because of delayed mating may originate in a nonadaptive response in control of apoptosis through mistiming of reproduction.     

Cessation of childbearing in the absence of contraception in Sri Lanka

In data from the Sri Lanka Fertility Survey, 1975, the cessation of childbearing is examined among women who have never used contraception. The sample consisted of 6810 currently or previously married women, 57% of whom reported that they had never used contraception. Cessation of childbearing is studied according to age and marriage duration. The variables analyzed are age at last birth, proportions infertile during the last 5 or 7 years, and the infertile open interval. The duration of breastfeeding is taken into account where necessary, and the contraceptive users and nonusers are compared where appropriate. Non-users tend to cease childbearing early, and therefore are infertile for longer periods during their marriages. It is probably age of the 1st child that influences decisions on future fertility. Among women aged 45-49 who married before age 20 and continued in their 1st marriage, mean age at last live birth in non-users, was 34.5 years, about 2 years earlier than in those who had used contraception. Non-users who married at any age below 30 years cease childbearing well below age 40. The proportion not currently pregnant and infertile over the past 5 years increases with marriage duration among the fertile non-users in each age group. When age at last birth and the duration of breastfeeding in the open interval are taken into account and the reference period is increased to 7 years, the period of infertility increases with marriage duration among nonpregnant non-users below age 45. The proportion of women who were currently not pregnant and had remained infertile over the past 7 years is higher among the older non-users whose 1st child was born more than 10 years ago.     

The pattern of reproductive life in a Berber population of morocco

Abstract

Reproductive patterns were studied from data collected in 1,450 Berber households in the province of Marrakesh, Morocco in 1984. Women aged 45–49 years had a mean of 8.9 pregnancies to achieve 5.7 living children. Social influences on fertility rates show the importance of tradition, particularly through time‐dependent variables such as age at marriage, waiting time to first birth, interbirth intervals, and duration of breastfeeding. Birth control does not appear to affect the tempo of fertility; rather, its main use is to bring the reproductive period to a close. The comparison of two subsamples of women separated by a 25‐year interval indicates an actual acceleration of the tempo of fertility by the reduction of waiting time to first birth and of interbirth intervals. The supposed ongoing process of demographic transition is not clearly observed in this population.     

Fertility at low and high altitude in central Nepal

Abstract

Data are reported on ages of menarche, first marriage and first childbirth, migration, venereal disease, birth control, birth spacing and on completed fertility rate in populations of Central Nepal living at low (8,500 feet) and high altitude (12,400 feet). The high‐altitude population reported a significantly lower completed fertility rate which could be partly accounted for by later age at marriage and first childbirth and increased birth spacing. Longer post‐partum ammenorhea and breast feeding did not account for the increased average pregnancy gap.     

Synchrony between growth and reproductive patterns in human females: Early investment in growth among Pumé foragers

Life history is an important framework for understanding many aspects of ontogeny and reproduction relative to fitness outcomes. Because growth is a key influence on the timing of reproductive maturity and age at first birth is a critical demographic variable predicting lifetime fertility, it raises questions about the synchrony of growth and reproductive strategies. Among the Pumé, a group of South American foragers, young women give birth to their first child on average at age 15.5. Previous research showed that this early age at first birth maximizes surviving fertility under conditions of high infant mortality. In this study we evaluate Pumé growth data to test the expectation that if early reproduction is advantageous, then girls should have a developmental trajectory that best prepares them for young childbearing. Analyses show that comparatively Pumé girls invest in skeletal growth early, enter puberty having achieved a greater proportion of adult body size and grow at low velocities during adolescence. For early reproducers growing up in a food‐limited environment, a precocious investment in growth is advantageous because juveniles have no chance of pregnancy and it occurs before the onset of the competing metabolic demands of final reproductive maturation and childbearing. Documenting growth patterns under preindustrial energetic and demographic conditions expands the range of developmental variation not otherwise captured by normative growth standards and contributes to research on human phenotypic plasticity in diverse environments. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc.     

An Old Mom Keeps You Young: Mother’s Age at Last Birth and Offspring Longevity in Nineteenth-Century Utah

This study analyzes the intergenerational effects of late childbearing on offspring’s adult longevity in a population in Utah (United States) that does not display evidence of parity-specific birth control—a so-called natural fertility population. Studies have found that for women who experience late menopause and prolonged reproduction, aging is postponed and longevity is increased. This is believed to indicate female “robustness” and the impact of biological or genetic factors. If indeed there is a genetic component involved, one would expect to also find evidence for the intergenerational transmission of longevity benefits. Our study investigates the relationship between prolonged natural fertility of mothers and their offspring’s survival rates in adulthood. Gompertz regression models (N = 7,716) revealed that the offspring of mothers who were naturally fertile until a relatively advanced age lived significantly longer. This observed positive effect of late reproduction was not independent of but conditional upon survival of the mother to the end of her fecundity (defined as age 50). Offspring’s relative risks at death beyond age 50 were 6–12 percent lower than those of their counterparts born to mothers who had an average age at last birth. Our results, which account for various early, adult, and later-life conditions, as well as shared frailty, suggest that there is a positive relationship between mother’s age at last birth and offspring longevity, and strengthen the notion that age at menopause is a good predictor of this relationship.     

A period analysis of parity distribution among white and nonwhite women in the United States, 1940–1974

Abstract

The historical trends of childlessness and of one‐child, two‐child, and three‐or‐more‐child families among white and nonwhite women in the United States are studied in terms of period fertility tables. Given the age and parity of a woman, we can read from the fertility tables how her parity is expected to change at successive ages during the rest of her childbearing period, if she is subjected to the age‐parity‐specific fertility rates for a particular year. The fertility tables for white and nonwhite women are constructed for the years 1940, 19S0, 1960, 1970, and 1974. These tables show that among white women who have completed their childbearing (with period rates), the percentage with more than two children has decreased from 66 in 1960 to 27 in 1974, whereas the corresponding reduction among nonwhite women is from 67 to 48 per cent (Table 1, Case 1).     

A regression approach to the projection of U.S. fertility based on past fertility data

Abstract

The method of fertility projection used by the U.S. Bureau of the Census involves assumptions about the ultimate cohort total fertility rate and the ultimate cohort mean age at childbearing based on recent levels of fertility and women's birth expectations. This paper provides an outline of a general regression approach to fertility projection based on past data which would generate these two ultimate cohort characteristics. The technique is illustrated by using the U.S. single‐year age‐specific fertility rates up to 1986 for total women and projecting them indefinitely into the future until they become stable for both calendar years and cohorts.     

Maternal age at last birth in Egypt

To assess the effects of women's education, residence, and marital experience on their age at the birth of their last child, a proportional hazards regression model was applied to 1980 Egyptian Fertility Survey (EFS) data. The detailed data include the date of birth of each child for every women interviewed, and the woman's date of birth and age at interview. Age at last birth was examined by regression analysis on birth history and socioeconomic information. 4 hypotheses were tested: women who are well educated have a greater probability of ending childbearing earlier than women with less education; women in rural areas have a higher probability of having their last child at older ages than urban women; marital disruption without remarriage lowers the probability of older maternal age at last birth; and marital disruption with remarriage increases the probability that a woman stops reproducing at an older age. The overall chi-square indicates a significant regression. All coefficients were significant, except the coefficient for women with intact 1st marriages. Women with more education had a greater probability of ending childbearing earlier than women with less education. Rural women tended to have their last children at ages significantly older than overall age at last birth. Current residence in urban areas had the opposite effect. The coefficient for those with intact 1st marriages was insignificant, meaning that the mean age at last birth for this group of women was not much different from the overall mean. Remarried women tended to end childbearing at ages significantly older than the overall average age at last birth, suggesting that these women tended to have children by their new husbands. Those with dissolved 1st marriages who had not remarried had a higher probability of ending childbearing earlier than did older women. Marriage age and final parity had highly significant negative coefficients; as marriage age and number of children born increased, so did the "survival" time or the age at last birth. Results from the hazards model indicate that the effects were as anticipated. The median age at last birth for the total sample of women aged 45-49 was 45-49 years. The median age at last birth was about 2 years older for rural compared to urban women. Illiterate women had the oldest median age at last birth of the education groups. There was little differences between median ages at last birth for women with intact 1st marriages and those whose 1st unions were dissolved and who had remarried. The median age at last birth increased with final parity.     

Pregnancy after cytotoxic chemotherapy for gestational trophoblastic tumours.

To examine the possibility that cytotoxic drugs may cause sterility or congenital malformations in the offspring of women of childbearing age who are cured of cancer a study was conducted of the obstetric histories of 445 long term survivors treated in this unit with chemotherapy for gestational trophoblastic tumours between 1958 and 1978. After completing treatment 97% of those who wished for a pregnancy (49% of all women studied) conceived and 86% had at least one live birth. All these women had received methotrexate. Of the 47 women who wished to conceive and whose combination therapy included cyclophosphamide, 37 (79%) had a live birth. Women who received three or more drugs were less likely to have a live birth than those who received methotrexate alone or with only one other drug (p less than 0.001). There was no statistically significant excess of congenital malformations. These results are strong evidence that the cytotoxic drug regimens used in this unit for treating gestational trophoblastic tumours are compatible with the preservation of fertility in most women and not associated with any increase in congenital abnormalities.     

Age and fertility: can women wait until their early thirties to try for a first birth?

Postponing the start of childbearing raises the question of fertility postponed versus fertility foregone. One of the limitations of previous studies of 'How late can you wait?' is that any observed decline in the probability of conception with age could be due to a decline in fecundability with age or due to a decline in coital frequency with age or due to both factors. Using data from a multinational longitudinal study conducted to determine the daily probability of conception among healthy subjects, a discrete-time event history model with long-term survivors (sterile population) is used to study the relationship between age and fecundability for childless women, while controlling for the pattern of intercourse within a menstrual cycle. The findings suggest that women can wait until their early thirties to try for a first birth, providing that they are not already sterile, as the magnitude of the decline in fecundability is very modest and of little practical importance.     

Age at menarche,socio‐sexual behavior,and fertility

Abstract

This paper examines the relationship between age at menarche and fertility from two perspectives. Age at menarche is regarded as a crude indicator of the timing of fecundity that may affect the timing of conception among those sexually active; and age at menarche is regarded as a crude indicator of the timing of sexual maturation that may influence the timing of socio‐sexual behavior, namely dating and sexual intercourse. The data are drawn from a survey of New York City women who recently had their first child. The findings suggest that age at menarche as an indicator of fecundity is not a good predictor of the timing of the first birth, when controlling for age at first sexual intercourse. Looking only at initial noncontraceptors, however, we find the relationship is stronger. Age at menarche, viewed as an indicator of the timing of sexual maturation, does seem to have some influence on the timing of dating, but only for Blacks. For both races, age at first date is related to age at first sexual intercourse.     

Variations in value orientations and fertility behavior

A test of a hypothesis regarding attitudes toward nature, time, familial relations, activity, and sex was undertaken. The hypothesis was: wives who have a modern orientation to any 1 of these items will expect a smaller number of children, will have smaller proportion of unplanned births, and will have lower fertility than wives who have traditional orientation. Data on which the study was based were obtained from a project on family formation and values conducted in Lexington, Kentucky, during the spring of 1968. Of the 403 eligible respondents (resident white nonfarm females who had a legitimate live birth in Fayette County, Kentucky during the period January 1, 1967, to December 31, 1967, 275 were interviewed. Results indicated 3 patterns: 1) sex orientation is not related to fertility expectations, or, at best, is weakly associated; 2) the sex orientation scale does not discriminate birth control effectiveness as predicted; and 3) sex orientation is associated with actual fertility, but in the opposite direction from that hypothesized. Women who have a modern orientation to sex have larger families than women with a traditional orientation, even though the former are more effective family planners. Results indicated that time orientation is not directly related to fertility behavior while the activity orientation is related to fertility behavior but in the opposite direction from that hypothesized. The nature and relational orientations provided some support for the hypothesized relation between modern orientations and low fertility behavior.     

Biological versus chronological ovarian age: implications for assisted reproductive technology

Background  

Women have been able to delay childbearing since effective contraception became available in the 1960s. However, fertility decreases with increasing maternal age. A slow but steady decrease in fertility is observed in women aged between 30 and 35 years, which is followed by an accelerated decline among women aged over 35 years. A combination of delayed childbearing and reduced fecundity with increasing age has resulted in an increased number and proportion of women of greater than or equal to 35 years of age seeking assisted reproductive technology (ART) treatment.     

Economic and social correlates of infant mortality: A cross‐sectional and longitudinal analysis of 63 selected countries

Abstract

Genealogical records containing birth and death dates for completed families have been analyzed to compare the longevity of twins, sibs and parents. The data are restricted to twins and sibs who survived to adulthood and married. The findings, similar to those found with respect to fertility (Wyshak and White, 1969), show that twins, especially male twins, are disadvantaged in comparison with their male sibs. Sib‐sib and parent‐offspring correlation analysis confirmed that there is a genetic component in the determination of life span, but environmental factors contribute more to the total variation. No evidence of a stronger maternal than paternal effect was found. Twin bearers also lived longer than nontwin bearers. Even among persons who survived to age SO or more, parents of twins had more children and lived slightly longer than their twin and nontwin offspring. Regression analysis for persons who survived to SO or longer indicated that, in addition to life span of parents, secularity (year of death) and fertility (number of children borne) were the best predictors of longevity, though only a small proportion of the variation could be accounted for by these and other demographic variables. Life span has shown a consistent increase over time from the seventeenth century through the nineteenth century, while fertility has tended to decline. However, among persons surviving to age SO, when the relation between secularity and fertility and secularity and longevity is controlled, a significant correlation between fertility and longevity remains. This relation, observed in populations that did not practice voluntary family size limitation, would not be found in contemporary data. Maternal mortality accounted for the shorter life span of women than for men; eliminating its effect gives women a slight advantage. The fertility and longevity experience of migrants who survived to age SO is more favorable than that of persons who did not migrate.     

Menarcheal age and subsequent patterns of family formation

Abstract

We examine whether age at menarche affects age at first marriage or first birth using two samples of U.S. women. Data are drawn from the Tremin Trust, a longitudinal study of menstrual cycles that recruited white women who were students at the University of Minnesota and from a survey of a nationally representative sample of white women born between 1900 and 1910. Regression models with cubic splines were used to analyze the relationship between age at menarche and age at first marriage. Cox proportional hazard models were used to examine the effect of age at menarche on the interval between marriage and first birth. Unlike earlier work, we found that once secular trends in both age at marriage and age at menarche were taken into account, there was no evidence that age at menarche affects either age at marriage or the timing of first births in these U.S. women.     

Do high-status people really have fewer children?

Evolutionary discussions regarding the relationship between social status and fertility in the contemporary U.S. typically claim that the relationship is either negative or absent entirely. The published data on recent generations of Americans upon which such statements rest, however, are solid with respect to women but sparse and equivocal for men. In the current study, we investigate education and income in relation to age at first child, childlessness, and number of children for men and women in two samples—one of the general American population and one of graduates of an elite American university. We find that increased education is strongly associated with delayed childbearing in both sexes and is also moderately associated with decreased completed or near-completed fertility. Women in the general population with higher adult income have fewer children, but this relationship does not hold within all educational groups, including our sample with elite educations. Higher-income men, however, do not have fewer children in the general population and in fact have lower childlessness rates. Further, higher income in men is positively associated with fertility among our sample with elite educations as well as within the general population among those with college educations. Such findings undermine simple statements on the relationship between status and fertility.