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PubMed2002

Does education mediate the relationship between IQ and age of first birth? A behavioural genetic analysis.

This study presents a multivariate behavioural genetic analysis of the relationship between education, intelligence and age of first birth. Analyses investigated the mediational role of education in explaining the relationship between intelligence and age of first birth at both the phenotypic and behavioural genetic level. The data come from the National Longitudinal Survey of Youth (NLSY), a nationally representative survey that included genetically informative full- and half-sibling pairs (n = 1423 pairs). Respondents were aged 14 to 22 when contacted in 1979. Heritability estimates were 0.32, 0.50 and 0.06 for IQ, education and age of first birth, respectively. Shared environment estimates were 0.35, 0.23 and 0.20 respectively. Common genetic and shared environmental factors were substantial in explaining the relationship between intelligence and education, and also education and age of first birth. Education partially mediated the relationship between intelligence and age of first birth only in the phenotypic analyses. After considering the genetic and shared environmental factors that influence all three variables, evidence for mediation was less convincing. This pattern of results suggests that the apparent mediational role of education at the phenotypic level is in fact the result of underlying genetic and shared environmental influences that affect education, IQ and age of first birth in common.

Adolescent↗
PubMed2006

[Effects of the late marriage of Korean women on the first-birth interval].

OBJECTIVES: The purpose of this study was to examine the effect of women's late age of marriage on the interval between marriage and their first birth. METHODS: Data from Year 2000 Korea National Fertility Survey was collected through direct interview questionings, and the data was analyzed based on randomly selected sampling. In particular, the married women (N=5,648) were analyzed for the factors that determined the first-birth interval by performing Cox's proportional hazard model survival analysis. RESULTS: Unlike previous findings, the woman whose age of marriage was 30 or more was more likely to delay the birth of her first baby than were the other women who married earlier. Further, a woman's age at marriage, a woman's residence before marriage, her husband's religion, her husband's level of education and the difference in age between the woman and her husband significantly influenced the first-birth interval. In contrast, for a married woman, her age, level of education, current residence and religion were not significant predictors of her first birth interval. CONCLUSIONS: Our study showed that women who married at the age of 30 years or more tend to postpone their first birth in Korea. When facing the increasing number of women who marry at a late age, the Korean government should implement population and social policies to encourage married women have their first child as early as possible.

Adult↗
PubMed2005

Changes in marriage age and first birth interval in Huaning County, Yunnan Province, PR China.

The timing of marriages, first birth interval and the prevalence of premarital conception (PMC) among women of successive birth cohorts in one rural county in Yunnan, China, were examined. Detailed pregnancy histories were collected for 1,336 women aged 15-64 years using a Life History Calendar. The rising marriage age and shorter first birth interval correspond to over-all changes in the Chinese society over the same time period. The mean age at first marriage for women born before 1950 was just below 20, and 22.5 among women born 1976-1980. The later marriage age was partly offset by the dramatic shortening of the first birth interval from over 30 months in the oldest cohort to 11-12 months in the youngest. One explanation of the shortening of the first birth interval may be the increase in premarital conception. Among the young women in our study almost one-third of first pregnancies were conceived before marriage.

Adolescent↗
PubMed1990

Age at first birth, parity and risk of breast cancer: a meta-analysis of 8 studies from the Nordic countries.

Several large epidemiological studies in the Nordic countries have failed to confirm an association between age at first birth and breast cancer independent of parity. To assess whether lack of power or heterogeneity between the countries could explain this, a meta-analysis was performed of 8 population-based studies (3 cohort and 5 case-control) of breast cancer and reproductive variables in the Nordic countries, including a total of 5,568 cases. It confirmed that low parity and late age at first birth are significant and independent determinants of breast-cancer risk. Nulliparity was associated with a 30% increase in risk compared with parous women, and for every 2 births, the risk was reduced by about 16%. There was a significant trend of increasing risk with increasing age at first birth, women giving first birth after the age of 35 years having a 40% increased risk compared to those with a first birth before the age of 20 years. Tests for heterogeneity between studies were not significant for any of the examined variables. In the absence of bias, this suggests that several individual Nordic studies may have had too little power to detect the weak effect of age at first birth observed in the meta-analysis.

Breast Neoplasms↗
PubMed1991

Recent trends in the timing of first births in the United States.

We use vital registration data published since 1979 to update trends in the timing of first births. Two important trends are documented. First, the likelihood that childless women over age 30 will have a first birth has increased since the 1970s. This change shows that women born in the 1950s are "catching up" on fertility postponed at younger ages. Second, racial differences in the timing of first births are very large. For those born in the 1950s, nonwhites have first births much earlier, and far fewer nonwhite than white women will remain permanently childless. In the second part of the paper, we use these data for recent years to assess earlier projections of childlessness based on cohort and period approaches. We also assess the accuracy of stated intentions to have no children.

Black or African American↗
PubMed2005

The age pattern of first-birth rates among U.S. women: the bimodal 1990s.

Between 1990 and 2002, the age pattern of Type I first-birth rates (i.e., the hazard of a first birth) among U.S. women was bimodal. This pattern, driven by changing differential fertility patterns among racial and ethnic groups, reached its apex at the mid-1990s and had almost vanished by the decade's end. Research on first-birth timing has tended to focus on Type II first-birth rates and therefore has failed to identify this larger, bimodal pattern. This article presents the benefits of using Type I rates, documents the emergence of the bimodal pattern via two new measures of bimodality, and uses a decomposition analysis to discuss the pattern's causes.

Adolescent↗
PubMedDate not supplied

Age at return marriage and timing of first birth in India's Uttar Pradesh and Kerala states.

The study investigates the relationship between age at marriage and the length of first birth interval in two states of India: Uttar Pradesh and Kerala. Life tables of first-birth intervals and median first-birth intervals are computed for several subgroups of the study population. Multivariate hazards modelling technique is used to study the net effect of age at marriage, controlling for a multiple of socioeconomic factors. The result shows that the average first-birth interval varies by age at marriage and is much longer in Uttar Pradesh than in Kerala.

Adolescent↗
PubMedDate not supplied

The effects of the sequencing of marriage and first birth during adolescence.

Whether or not they marry, black adolescent mothers are more likely than whites to attend school following the birth of their first child. Marrying to legitimate a birth reduces the likelihood that a teenager will return to school after childbearing; this impact of marriage is much stronger among black than among white teenagers. The timing of marriage appears to affect school enrollment among white teenagers through its impact on living arrangements. However, the negative impact of marriage on educational achievement does not seem to be a consequence of earlier differences in educational expectations among the teenagers. Teenage mothers appear less likely to separate from their husbands in later years if they marry before the birth than if they marry afterward. Delaying marriage until after the birth has a long-term effect on the probability of separation among white teenage mothers, but has only a short-term impact among blacks. Among teenagers who marry before giving birth, there is little difference in the likelihood of separation between those who marry before becoming pregnant and those who do so afterward. In addition, the effect of the sequence of marriage and first birth among white teenage mothers may have declined in recent years. Adolescent mothers who do not marry before their first birth experience a longer interval between that birth and their second than do those who marry either before or during the pregnancy. These differences are primarily the result of short-term variations in the amount of time they spend married; that is, women who are unmarried when they give birth are less likely to have a second birth soon afterward.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1981

Early age at first birth and decreased risk of breast cancer.

The relationship between age at birth of a first child and breast cancer was evaluated for 1159 affected women and 11,590 women without cancer in data collected in 1976 among married female registered nurses residing in 11 states in the United States. A positive trend of increasing risk of breast cancer with later ages at first birth was found (chi 2(1) for trend in proportions = 30.9, p less than 0.01). Adjustment for potential confounding variables by multiple logistic regression did not affect this trend. The presence of this relationship using non-hospitalized controls of similar social status to cases supports the reality of this association, which has recently been challenged as an artifact due to inappropriate choice of hospitalized controls.

Adult↗
PubMed1981

Radiographic patterns of the mammary parenchyma: variation with age at examination and age at first birth.

Mammograms of 15,110 women, representing a random selection of all 45-69-year-old women living in Malmö and taking part in screening for carcinoma of the breast, were analyzed using Wolfe's criteria for variations in the parenchymal pattern with (a) age at examination and (b) age at the birth of her first child. P2 and DY, which are considered high-risk patterns, increased in frequency with advancing age at first birth, being highest in nulliparous women, but decreased with age at examination.

Adult↗
PubMed1989

Children, age at first birth, and colorectal cancer risk. Data from the Melbourne Colorectal Cancer Study.

During 1980 and 1981, data were obtained on the number of children and age at birth of the first child in 675 cases of colorectal cancer and in 720 age-sex frequency-matched controls as part of a large epidemiologic study of colorectal cancer conducted in Melbourne, Australia. For colorectal cancer, the relative risk (RR) for those with one or more children compared with those with no children was statistically significantly lower than one (RR = 0.61, 95% confidence interval (CI): 0.45-0.81, p less than 0.001), and with simultaneous adjustment for number of children, there was an increasing risk with increasing age at birth of first child (RR = 1.03, with each increasing year of age at birth of first child, 95% CI: 1.00-1.05, p = 0.02). The relation between both the number of children and the age at birth of the first child and colorectal cancer risk was not statistically significantly different for males and females. The risk of colorectal cancer with respect to number of children and age at birth of the first child was unaffected by the potential confounding factors of age, occupation, previous diet, oral contraceptive use in females, and a family history of colorectal cancer. Since the protection against colorectal cancer associated with having children and with earlier age at birth of the first child was found to be similar for both males and females in the Melbourne study, a life-style factor, as yet unidentified, rather than a female hormonal factor, is postulated as the mediator of these effects.

Aged↗
PubMed1996

Distribution of time of first birth in presence of social customs regulating physical separation and coital frequency.

The interval between marriage and the first birth in India, particularly in rural areas, is much longer than what is observed in western countries. In eastern Uttar Pradesh, the mean interval is observed to be even longer, possibly due to traditional customs such as the female partner's visits to her parents in the early years of marriage and the smaller chance of coition because of the observance of rigid intercourse taboos. Thus the models to explain the length of the interval of marriage to first birth proposed by Western demographers, which assume that the period of cohabitation between marriage and first birth is uninterrupted, often do not describe the data satisfactorily when applied to rural India. In this paper a model to describe data on first birth interval is proposed that takes account of the distributions of timing and periods of physical separation and variation in fecundity with effective marriage duration.

Adolescent↗
PubMed1989

A prospective study of the independent effects of parity and age at first birth on breast cancer incidence in England and Wales.

The independent effects of parity and age at first birth on breast cancer incidence are investigated in a 1% sample of women aged 16 to 59 from the 1971 Census of England and Wales. Over the period 1971-81, 1,003 breast cancer cases occurred in the cohort of 113,263 women who were either married, widowed or divorced at the time of Census. Age at first birth was positively related to breast cancer risk, women giving birth to their first child after 35 years being at greater risk than nulliparous women. This effect remained, after adjustment for number of live-born children. Breast cancer risk showed a statistically significant decline with increasing parity even after adjustment for age at first birth. These results are consistent with other published evidence which suggests that other births subsequent to the first have an independent effect on breast cancer risk.

Breast Neoplasms↗
PubMed1970

Age at first birth and breast cancer risk.

An international collaborative study of breast cancer and reproductive experience has been carried out in 7 areas of the world. In all areas studied, a striking relation between age at first birth and breast cancer risk was observed. It is estimated that women having their first child when aged under 18 years have only about one-third the breast cancer risk of those whose first birth is delayed until the age of 35 years or more. Births after the first, even if they occur at an early age, have no, or very little, protective effect. The reduced risk of breast cancer in women having their first child at an early age explains the previously observed inverse relationship between total parity and breast cancer risk, since women having their first birth early tend to become ultimately of high parity. The association with age at first birth requires different kinds of etiological hypotheses from those that have been invoked in the past to explain the association between breast cancer risk and reproductive experience.

Adolescent↗
PubMed2005

Trends in cesarean rates for first births and repeat cesarean rates for low-risk women: United States, 1990-2003.

OBJECTIVES: This report presents trends in cesarean rates for first births and repeat cesarean rates for low-risk women, in relation to the Healthy People 2010 (HP 2010) objectives. Data for the U.S. showing trends by maternal age and race and Hispanic origin are presented. METHODS: Cesarean rates were computed based on the information reported on birth certificates. RESULTS: With a decrease between 1990 and 1996 and an increase between 1996 and 2003, the trend in the cesarean rate for low-risk women having a first birth paralleled trends in the primary (regardless of parity) and total cesarean rates. During 1996-2003 the cesarean rate for low-risk women having a first birth has consistently been at least 13 percent lower than the rate for all women having a first birth. For 2003 the cesarean rate for all primiparous women was 27.1 percent; for low-risk women the rate was 23.6 percent. The trend in the repeat cesarean rate for low-risk women was similar to the trend in the repeat rate for all women, i.e., a decrease from 1990 to 1996 and an increase from 1996 to 2003. The repeat cesarean rate for low-risk women has consistently been slightly lower than the rate for all women. For 2003 the repeat rate for all women was 89.4; the rate for low-risk women was 88.7. These trends were found for low-risk women of all ages and racial or ethnic groups. Therefore, low-risk women giving birth for the first time who have a cesarean delivery are more likely to have a subsequent cesarean delivery.

Adult↗
PubMed2004

Maternal blood pressure in pregnancy, birth weight, and perinatal mortality in first births: prospective study.

OBJECTIVE: To investigate the relation of diastolic blood pressure in pregnancy with birth weight and perinatal mortality. DESIGN: Prospective study. SETTING: 15 maternity units in one London health region, 1988-2000. PARTICIPANTS: 210 814 first singleton births of babies weighing more than 200 g among mothers with no hypertension before 20 weeks' gestation and without proteinuria, delivering between 24 and 43 weeks' gestation. MAIN OUTCOME MEASURES: Birth weight and perinatal mortality. RESULTS: The mean (SD) birth weight of babies born to mothers with no hypertension before 20 weeks' gestation or proteinuria was 3282 g (545 g) and there were 1335 perinatal deaths, compared with 94 perinatal deaths among women with proteinuria or a history of hypertension. Diastolic blood pressure at booking for antenatal checks was progressively higher from weeks 34 to 40 of gestation. The birth weight of babies being delivered after 34 weeks was highest for highest recorded maternal diastolic blood pressures of between 70 and 80 mm Hg and lower for blood pressures outside this range. Both low and high diastolic blood pressures were associated with statistically significantly higher perinatal mortality. Using a linear quadratic model, 94 of 825 (11.4%) perinatal deaths could be attributed to mothers having blood pressure differing from the optimal blood pressure (82.7 mm Hg) predicted by the fitted model. Most of these excess deaths occurred with blood pressures below the optimal value. CONCLUSIONS: Both low and high diastolic blood pressures in women during pregnancy are associated with small babies and high perinatal mortality.

Adolescent↗
PubMed1989

Timing of first birth and second birth spacing in Canada.

In Canadian society the influence of first birth timing on the subsequent birth interval has been eroded over time, as shown by the Canadian Fertility Survey of 1984. The influence of first birth timing is significant for second births among women married during the baby boom period, but not for those married thereafter. Religiosity, marital status, and place of residence are significant factors in second birth timing in Canada.

Adolescent↗
PubMed1993

Writing the names: marriage style, living arrangements, and first birth interval in a Nepali society.

Using data from a Nepali population, this analysis argues that marriage style and postmarital living arrangements affect coital frequency to produce variations in the timing of first birth after marriage. Event history analysis of the first birth interval for 149 women suggests that women's autonomy in marriage decisions and marriage to cross-cousins accelerate the pace of entry into first birth. Extended-household residence with reduced natal kin contact, on the other hand, significantly lengthens the first birth interval. These findings are consistent with previous arguments in the literature while offering new evidence for the impact of extended-family residence on fertility.

Adolescent↗