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PubMed1991

[A multivariate model for first births].

"The objective of this study was to construct a multivariate model to explain individual differences in first birth, using economic and sociological fertility theories and the findings from past analyses on data from the Netherlands Fertility Survey.... The explanatory variables found to be significant are age at first birth, household position, labour force participation, educational level, and period of first birth.... The parameters of the model can be used to calculate the probability to remain childless for women with a specific life cycle." (SUMMARY IN ENG)

Age Factors↗

PubMed1984

Forecasting first births.

This study is concerned with one aspect of the family cycle, namely, the transition from young married to young married with small children. The focus is on developing models to forecast entries into this latter stage for the purpose of marketing research. "Using ordinary least squares, forecasting models were estimated for (1) total number of first births, (2) number of white first births, and (3) number of nonwhite first births." Models are estimated for both the United States and California using data from official sources.

Black or African American↗

PubMed1995

Slow twin conception at first birth and subsequent maternal twin proneness in a natural fertility population.

To study whether apparently more fecund women having delivered twins at first birth have traits of higher twin-proneness, we performed a retrospective cohort study on population-based historical vital records of the 17-18th century French Canadian immigrants and their descendants under natural fertility conditions. Among 24896 mothers who had at least one child, 248 had twin maternities at their first birth (twinning rate = 1.0%). Among 21508 mothers with a valid marriage-first birth interval, twinning rate was 0.97% among prompt conceptions (7.0-11.0 months), with a particularly high rate at the interval of 7.0-8.0 months (2.2%). Marriages in August-October resulted in a higher twinning rate particularly for the slow conceptions than those in the other seasons. Promptly-conceived mothers of twins at the first delivery may seem to have higher fecundity, but subsequent births from these mothers (n = 88) show a lower twinning rate (1.7%) particularly at younger maternal age than from the other mothers who had slowly conceived twins at their first birth (n = 112). The latter show a 4.5% twinning rate as a whole among their second or later births. So-called twin-proneness of a mother, whether genetic or acquired, was not connected to higher conception rate of twin's mothers immediately after marriage. Reduced fecundity, which may have been imposed by some environmental factors, could raise the chance of twinning.

Adult↗

PubMed2024

Causal effect of the age at first birth with depression: a mendelian randomization study.

BACKGROUND: This study aimed to explore the causal relationship between age at first birth (AFB) and depression. METHODS: Using the univariable Mendelian randomization (UVMR) and multivariable Mendelian randomization (MVMR) methods to examine the potential correlation between age at first birth (AFB) and major depressive disorder and postpartum depression. A public database was used to obtain the genome-wide association studies (GWAS) summary data. We put inverse-variance-weighted (IVW) as the primary method in Mendelian randomization (MR) analysis and used sensitivity analysis to confirm the robustness of our result. RESULTS: We found a significant causal association between AFB and major depressive disorder by using the IVW algorithm (odd ratio [OR] 0.826; 95% confidence interval [CI] 0.793 - 0.861; P = 4.51 × 10- 20). MR-Egger, weighted median, simple mode and weighted mode method concluded the same result (P < 0.05). During the sensitivity analysis, the heterogeneity test (Q-value = 55.061, df = 48, P = 2.81 × 10- 01, I2 = 12.82%) and the leave-one-out plot analysis confirmed the stability of the results. The outcomes of the pleiotropy test (MR-Egger intercept = 8.932 × 10- 3. SE = 6.909 × 10- 3. P = 2.02 × 10- 01) and MR_PRESSO global test (P = 2.03 × 10- 01) indicated there is no pleiotropy. CONCLUSION: There is solid evidence that a higher age at first birth is associated with a lower risk of major depressive disorder.

Humans↗

PubMed1999

Effects of the status of women on the first-birth interval in Indian urban society.

The status of women, which is relative and multidimensional, has an important bearing on any long-term reduction in fertility. In Indian society, where cohabitation and childbearing are socially sanctioned only after marriage, the length of the first-birth interval affects the completed family size by influencing the spacing and childbearing pattern of a family. This study examines the influence of certain aspects of the status of married women--education, employment, role in family decision making, and age at marriage--along with three socioeconomic variables--per capita income of the family, social position of the household, and the caste system--on the duration of the first-birth interval in an urban Hindu society of the north-east Indian state of Assam. The data were analysed by applying life table and hazard regression techniques. The results indicate that a female's age at marriage, education, current age, role in decision making, and the per capita income of the household are the main covariates that strongly influence the length of the first-birth interval of Hindu females of urban Assam. Of all the covariates studied, a female's education appears to be a key mediating factor, through its influence on her probability of employment outside the home and thereby an earned income and on her role in family decision making. Unlike other Indian communities, the effect of the caste system does not have a significant effect on first-birth timing in this urban Hindu society.

Adolescent↗

PubMed2002

Oral contraceptive use before first birth and risk of breast cancer: a case control study.

BACKGROUND: The aim of this study was first, to investigate whether women starting oral contraceptive (OC) use at a young age and before first birth have an increased risk for breast cancer and second, to report difficulties encountered in studying long-term health impacts of medical technologies. METHODS: Breast cancers occurring up until 1997 among 37153 Helsinki students born between 1946 and 1960 were identified by record linkage from the Finnish Cancer Registry; for each cancer case, five age-matched random controls were picked from the same student population. Those who had used the Helsinki Student Health Service (HSHS) at least three times (150 cases and 316 controls) form the final study subjects. Data on OC use and background characteristics were collected from patient records, and data on live births were derived from the population register. Odds ratios (OR) were adjusted for number of births, smoking and sports activity. RESULTS: Compared to the few non-users, OC users had a higher risk of breast cancer: the adjusted OR was 2.1 (95% confidence interval 1.1-4.2). Among OC users, no statistically significant differences in risk of breast cancer were found in regard to starting age or first birth, but small numbers made confidence intervals wide. Even though we had chosen students to be our study group, the population turned out to be unsuitable to answer our research question: most women had started their OC use old (at the age of 20 or later) and there were very few unexposed (almost all had used OC and before their first birth). CONCLUSIONS: Because adoption of the modern pattern of OC use was not common among students, it is unlikely that the impact of early and extended OC use can be studied before 2010, when women born in the 1960s are 40 to 50 years old.

Journal Article↗

PubMed1991

Intervals between marriage and first birth in mothers and daughters.

Marriage-first birth intervals are examined in two historical populations, Quebec (1608-1765) and Haut-Jura (1689-1980), comparing intervals in mothers and daughters, and in sister-sister pairs. The results point to a weak relationship between intervals of mothers and daughters, though it does not attain significance. Shared environment does not seem to be responsible since there is no association between pairs of sisters from the same populations.

Adolescent↗

PubMed1986

Age patterns of women at marriage, cohabitation, and first birth in India.

The purpose of this paper has been to examine the age patterns of Indian women at marriage, cohabitation, and first birth. This task is complicated by features of the Indian marriage institution that differentiate it from the institution of marriage in Western cultures. It is also complicated by the diversity of Indian marriage customs and by the possibility that Indian marriage patterns have changed over time. Nevertheless, our analysis of survey data for two districts in south central India support the following conclusions: Marriage and childbearing have been and continue to be universal. The timing of marriage and childbearing, which showed only a small increase over a fairly long period of time, appears more recently to be undergoing some changes in the direction of longer delays. The significant rural-urban differences in marriage and fertility timing are at least partly the result of the greater impact of education on age at marriage, cohabitation, and first birth in urban areas than in rural areas. Observed characteristics such as religion and education explain more variation in women's marriage and fertility timing in urban areas than in rural areas (i.e., education seems to generate new social norms that tend to displace norms derived from tradition. The incidence of childhood marriages and two-stage marriages has been on the decline, causing the small but noticeable rise in age at marriage to exceed somewhat the increase in age at cohabitation. Age patterns of marriage in India do not closely resemble Western patterns, although age patterns of cohabitation and first birth do. And socioeconomic variables appear to explain less variation in marriage and fertility timing within local communities than across communities. Most important, the results highlight the need for more recent and richer data on marriage and fertility behavior in India. In particular, they strongly suggest that marriage patterns in India are now in the midst of major changes. This conclusion is similar to that reached by Caldwell, Reddy, and Caldwell (1983), who adopted a more qualitative approach to analyzing marriage change than ours, but whose observations are also more recent than ours. Through the collection and analysis of more recent and geographically widespread data, we can begin to assess more fully the nature and magnitude of the demographic changes under way and speculate on their implications for population growth, economic development, and the formulation of public policy in India.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗

PubMed1980

Age at first birth, parity and risk of breast cancer in a Swedish population.

A case-control study was conducted over a period of 11 months in an area containing one-third of the Swedish population. One thousand and one patients participated, constituting 94% of all women newly diagnosed as having breast cancer within the area. They were compared with 1,001 age-matched, non-hospitalized controls without breast cancer, selected by paired sampling from a population register. The risk of breast cancer was slightly, but significantly, related to parity, the standardized relative risk (SRR) being 1.35 for nulliparous women as compared to ever parous. In the different parity groups a risk significantly lower than that for nulliparous women was found only for women with more than 2 children (SRR = 0.59) but the trend with parity was highly significant (P less than 0.001). Age at first birth was not found to be an important risk factor for breast cancer. SRR was lower than for nulliparous women in all groups of women with their first birth before the age of 35 years, but the difference was significant (P less than 0.05) only for those with the first birth between 20 and 24 (SSR = 0.69) and 25 and 29 (SRR = 0.69) years of age. The trend with age at first birth (P less than 0.05) disappeared after stratification for parity, suggesting that it was a confounding factor.

Adult↗

PubMed1981

Effects of the timing of marriage and first birth of the spacing of subsequent births.

Analyzing data from a fifteen-year follow-up survey of high school students originally surveyed in 1957-58 and resurveyed in 1973-74, this paper examines the effects of the timing of marriage and first birth on subsequent childspacing, holding constant the effects of other variables that may be sources of spuriousness. The results suggest that age at first marriage has a causal effect on the occurrence of a short first birth interval and that age at first marriage and premarital pregnancy interact in their effect on the occurrence of a short second birth interval. Age at first marriage has no causal effect on the spacing of the second birth for those whose first child was maritally conceived. The spacing of the first birth, however, appears to have a causal effect on the spacing of the second.

Adult↗

PubMedDate not supplied

Marriage, remarriage, marital disruption and age at first birth.

Out-of-wedlock pregnancy, especially for a teenager, and even more for a black teenager, hastens early marriage. The younger the age at first birth, the likelier that the first marriage will dissolve. White women are more likely than black women to remarry. Women under 20 at first birth are more likely to have their second marriage dissolve.

Adolescent↗

PubMedDate not supplied

The age at menarche and age at first birth in an undernourished population.

A statistically significant relationship has been found between the age at menarche and the age at first birth among chronically-malnourished, lower-class Viennese women born in the late nineteenth century. Because the age at menarche depends on nutritional status, the above relationship is an indication that nutritional status must also have correlated positively with fertility rate, and therefore with population growth in societies with similar characteristics as this sample. Thus, the nutrition sensitivity of the age of first birth, and therefore of population growth are established in a chronically malnourished non-contraceptive historical population.

Austria↗

PubMed1998

Parity, age at first birth and the risk of carcinoma in situ of the breast.

Epidemiological studies of in situ breast cancer are sparse, and the role of reproductive history, an established risk modifier for invasive breast cancer, remains incompletely investigated. To examine possible associations with parity and age at first birth, we undertook a case-control study nested in a nationwide cohort of Swedish women. The reproductive history of 1,368 women aged 65 or younger with a diagnosis of carcinoma in situ of the breast were compared with that of 6,837 age-matched controls drawn randomly from a population-based Fertility Registry. Statistical analyses were performed by conditional logistic regression. Compared to nulliparous women, ever-parous women were at a reduced risk of carcinoma in situ of the breast. The risk decreased with number of live births, with the estimated risk reduction in the highest parity group (5+), being of the same magnitude as that reported for invasive breast cancer. By contrast, a positive association with increasing age at first birth was somewhat less pronounced than that observed previously in the same data set with respect to invasive breast cancer. Our findings indicate that parity affects the risk of invasive breast cancer and carcinoma in situ similarly, whereas the effect of age at first birth appears to be weaker for the risk of carcinoma in situ.

Adult↗

PubMedDate not supplied

Immaculate conceptions in sub-saharan Africa: exploratory analysis of inconsistencies in the timing of first sexual intercourse and first birth.

Survey data from a number of developing countries show that a considerable proportion of parous women report that they had their first birth one or more years before they first had sexual intercourse. In this paper, I use data from eight African Demographic and Health Surveys to explore factors that contribute to cross-national differentials in the prevalence of these "immaculate conceptions." The results suggest that this data problem results not only from recall errors, but also from the fact that some respondents misinterpret the question on first sexual intercourse and report their age at the onset of intercourse with either their first or current husband rather than their age at sexual initiation.

Adolescent↗

PubMed1992

Interpreting demographic effects in duration analyses of first birth intervals.

"Estimated demographic effects in proportional hazard models of first birth intervals could reflect time-invariant differences in the risk of a birth, or differences in the timing of a shift in the risk, or both. This paper attempts to distinguish between these possibilities. The procedure is to estimate a more general model than the proportional hazard specification, in which the evolution of the risk of a birth can differ with demographic characteristics. The proportional hazard specification is nested within this more general model. Consequently, the consistency of the data with the 'risk' or the 'timing' interpretation of demographic effects can be tested. The data studied do not lead to a rejection of the proportional hazard specification." Data are from the 1984 U.S. National Longitudinal Survey Youth Cohort and concern 670 women aged 16 or 17 in 1979.

Americas↗

PubMed1986

Age at first birth, dietary practices and breast cancer mortality in various Italian regions.

Breast cancer death certification rates in Italy showed a consistent geographic variation, with approximately a 2-fold ratio between the highest rates registered in Northern (and richer) regions, and the lowest ones in the South. This variation in breast cancer mortality was positively and strongly correlated with mean age at first birth (r = + 0.73). This positive correlation could not be totally explained by several other economic or dietary variables considered, though some of them substantially reduced the strength of the association. Breast cancer mortality rates were found to be positively correlated with milk, meat and sugar consumption, and negatively with pasta, thus confirming previous studies on national or international scales. These correlation coefficients, however, were considerably reduced after controlling for mean age at first birth. Further, when allowance was made for economic variables and age at first birth, only the correlation coefficients for milk and cheese remained significantly positive. Thus, the evidence from this study suggests that the Italian geographical correlations between breast cancer mortality and dietary variables may be largely explained in terms of reproductive factors, though there may be some effect of dietary variables on breast cancer risk as well.

Adult↗

PubMed2004

Relative influences on recent changes in the first birth ratio in the United States.

Researchers in psychology have focused a great deal of attention on the potential greater predisposition to achievement among first-born children relative to their siblings. Focusing on the United States as an example, a time series of the first birth ratio is used to show how the changing prevalence of first births relative to higher order births has altered the composition of birth cohorts, and the ratio is decomposed into four factors. Results show that the ratio increased significantly in the 1960s and early 1970s, but changed only slightly in the following decades. While more recent birth cohorts are composed of larger proportions of first-born children, the majority of children are still born as siblings. Contrary to expectations, the primary source of change was the proportion childless rather than decreasing higher order birth rates.

Adolescent↗

PubMedDate not supplied

[Age at the time of the first birth: a variable with simple, double, or triple significance in breast cancer studies].

I.--The inverse relationship of risk with parity is one of the earliest known features of the epidemiology of human mammary cancer. But recently knowledge of this relationship was refined when Mac Mahon and his colleagues found that the protective effect is actually correlated to the age of the mother at the first birth rather than to the total number of children, so that a woman who has a child before the age of 18 is one third as likely to suffer breast cancer in later life as a woman first delivered at 35. II.--A study was undertaken in the Centre Francois Baclesse on the hypothesis that age at first birth may also be related to the age of the patient at clinical onset of the mammary malignancy. One would expect to find a retardative effect of early delivery since this factor was found to be protective as far as mammary cancer risk is concerned. The conclusions of our investigations are in complete opposition to the original hypothesis: in our series, breast cancer appears to occur significantly earlier in women whose first delivery occurred early. III.--Thus the same process appears to be protective as far as total mammary cancer risk is concerned but accelerating as far as age at tumor onset is concerned. These apparently inconsistent observations led to the hypothesis that both studies might express the same biologic process which, in the case of early delivery, inhibits the mechanism of carcinogenic induction and therefore reduces the total number of cancer but which subsequently quickens the evolution of the inducted disease. Such a conjecture implies that breast cancer should be more severe following early first birth. The analysis of our series, as well as the series of Ontario Cancer Clinics, substantiates this hypothesis. But these conclusions are built on indirect proofs or direct proofs which are still short of statistical significance.

Adolescent↗