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PubMed1989

[[Proportional hazards model analysis of women's reproductive career in present-day Japan]].

The 1st section of this paper, using a method to decompose a change in the total marital fertility rate into the quantum and tempo effects, confirmed the major effect of birth timing on the 1970s trends in the total marital fertility rate based on the pooled data of the 8th and 9th Japanese National Fertility Surveys of 1982 and 1987, respectively. In the next section, proportional hazards model analyses of the 1st, 2nd, and 3rd birth functions for the pooled data made it clear that the 1st and 2nd birth intervals among the marriage cohorts since the end of the 1960s were shorter than those in the early 1960s even after having controlled for other variables. Given that 1 conception or more can occur during a birth interval, proportional hazards model analyses were again utilized to examine the effects of various variables on the time elapsed since marriage and the 1st conception, the time between the end of the 1st pregnancy and the 2nd conception, and the time between the end of the 2nd pregnancy and the 3rd conception. The authors found that the 1st-conception probability of the marriage cohorts since the late 1960s was smaller than that of predecessors, while the 2nd-conception probability was not affected by marriage cohort. In the last section, a logistic regression analysis of the probability of induced abortion showed that the probability of aborting a 2nd pregnancy decreased in the 1970s compared with that in the early 1960s. When a proportional hazards model analysis of the 2nd birth function was applied after omitting those cases where the 1st pregnancy did not result in birth and/or the 2nd pregnancy was aborted, the strong effect of marriage cohort on the 2nd birth probability was substantially diluted. These facts suggest that the shortened 2nd birth interval in the 1970s was partly caused by the shrinking probability of aborting a 2nd pregnancy in this period.

Abortion, Induced↗
PubMed1993

Emerging patterns of child-spacing in Canada.

This study used data from the 1984 Family History Survey conducted by Statistics Canada to examine recent trends and patterns of child-spacing among currently married women. Life table and proportional hazards estimates show that Canadian women, particularly those in younger age groups with higher education and longer work experience, start having children late, but have subsequent children rather quickly. This suggests that such women tend to complete childbearing within a compressed time period.

Adolescent↗
PubMed1990

Immunoglobulin haplotypes: markers of reproductive success?

Immunoglobulin haplotypes are highly polymorphic and are useful for analyses of both macro- and microdifferentiation of populations. The origins of this diversity are not known, but recent reports suggest strong selection at this locus. Increased rates of first-trimester spontaneous abortions have been reported when parents share GM phenotypes. Reduced fertility has been observed in mixed European descent white and Hutterite populations when both parents share immunoglobulin haplotypes. Population samples with completed family information and GM haplotype data are rare; the objective here is to provide this information on another sample. A sample of 242 Mennonite couples with mothers older than 40 years was divided into 3 groups of matings based on how many haplotypes were shared: 0, 1, or 2. The distribution of mean completed family sizes for the three groups were 3.35 +/- 1.85 (n = 23), 3.47 +/- 1.69 (n = 128), and 3.37 +/- 1.60 (n = 91), respectively; these values were not significantly different (F = 0.145, p = 0.865). The log-rank test was used to compare the time-to-next-birth curves. The intervals between first and later births (2-4 births) were not significantly different for the three subgroups either. There is also only limited evidence for segregation distortion in another sample of 923 offspring (in which at least one parent is heterozygous.

Abortion, Spontaneous↗
PubMed1983

A prospective cohort study of oral contraceptives and cancer of the endometrium.

A prospective cohort study of approximately 97 300 women was conducted in eastern Massachusetts. Information on use of oral contraceptives, and on gynaecological and reproductive histories was sought through mailed questionnaires, while newly diagnosed cases of cancer of the endometrium were identified from records of 34 area hospitals. Oral contraceptive (OC) use was associated with some increase in endometrial cancer rates (standardized rate ratio = 1.4; 95% confidence interval = 0.9-2.4), although the risk did not vary consistently by length of use, years since first use, or age at initial use. Although some subgroups of users had rates of disease higher than among nonusers, there was little to suggest a consistent association between OC use and incidence of endometrial cancer.

Adult↗