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PubMed1987

[Some aspects of the first and second birth interval].

"This article presents an analysis of the influence of demographic, socio-cultural and socioeconomic variables on the birth spacing pattern of women [in the Netherlands] with the aid of data from the Netherlands Fertility Survey 1982 and the follow-up study in 1985 (NFS'82/'85). Only the first and second intervals of women married for the first time and born between 1945-1964 are taken into account." The results indicate that 18 percent of the variance in the length of the first birth interval is due to such factors, suggesting that the influence of personal factors on fertility behavior is substantial. However, such variables account for only 8 percent of variance in the length of second birth intervals. (SUMMARY IN ENG)

Birth Intervals↗

PubMedDate not supplied

How does variation in fetal loss affect the distribution of waiting times to conception?

Unmeasured variation has long been a concern in analyses of the waiting time to conception. Recent work by Heckman and Walker (1991) and Trussell and Rodriguez (1990) has underscored the fact that statistical considerations alone cannot discriminate among likely models describing the distribution. Here, we specify a single theoretically important source of heterogeneity, namely variability in intrauterine mortality, and assess its effects on the waiting times to a conception which results in a live birth. We find that the effects on the waiting times to a conception which results in a live birth. We find that the effects of variation in fetal loss are confined to the tail of the distribution. Unless variation in fetal loss is extremely large or a substantial proportion of observed waiting times are initiated at late ages, variation in fetal loss does not appear to explain much variation in conception waits. We conclude that heterogeneity in fetal loss does not explain the variation in fecundability that has been observed for first birth intervals. This conclusion supports the hypothesis that at early ages (below age 35) variation in the waiting time to a fertile conception may largely reflect the proportion of nonsusceptible couples in the population. The analyses suggest that for the purposes of testing theoretically motivated models, future efforts should be directed toward examining reproductive experience after age 35 and toward incorporating information on characteristics of the fertile period as it becomes known.

Abortion, Spontaneous↗

PubMed2001

Starting, spacing and stopping in the reproductive histories of outer Hebridean families.

Maternal ages at the first maternity (starting), at the last maternity (stopping) and the lengths of intervals between maternities (spacing) have been studied in the Outer Hebridean islands of Harris and Barra for births between the years of 1855 and 1990, a period during which a considerable 'fertility transition' occurred. There was a tendency in each island for increases with time in the ages at starting among less-fecund women (although after 1936 starting ages declined), and highly significant heterogeneity of covariance: adjusted means dependent on the total numbers of maternities experienced. The same result was seen for the ages at stopping. Lengths of reproductive life (the difference between ages at starting and stopping) rose to 1876-1895, and then fell, apart from a short-lived rise in Barra during 1956-1975, possibly due to the papal encyclical Humaneae Vitae. Intervals between marriage and first maternity and between successive maternities were studied by hazard function survival analysis. The marriage first birth interval remained very constant, unaffected by total maternities. The father's occupation and the mother's age at first maternity showed no significant relationships. In Barra there was a weak negative relationship with the date of the marriage. For intervals between maternities in both islands, total maternities and the death of a previous infant were associated with shorter, and birth order with longer intervals. In Harris, there were tendencies for intervals to be consistently long or short in families, and for the age of the mother and date at first maternity to be negatively related to the length of the interval. In Barra, a previous multiple birth was followed by a longer interval. The date of the previous maternity, father's occupation, maternal age at the previous maternity, the sex of the previous child, and the duration of the marriage appeared to have no influence on maternity intervals. Evidence for an effect of economic deprivation during the 19th century on the variables considered was equivocal. During the 20th century, it is suggested that economic depression during the inter-war years, the spread of contraception, and improvements in health care may have acted 'synergistically' to produce the lower ages of childbearing and the shortening of maternity intervals and reproductive lives.

Adolescent↗

PubMed1982

The family formation process among U.S. marriage cohorts.

The family formation process is viewed as the progression of women through first marriage, first, subsequent, and last births and is examined for differential patterns of timing in 1930-1969 marriage cohorts. Based on the childbearing histories of approximately 17,000 white women once and still married, extracted from the June 1975 Current Population Survey, the study uses a dynamic model to show the varying importance across cohorts of the first birth interval as an important indicator of the total time spent in childbearing, social background effects in differentiating the timing of the first two births, and of prior birth transitions as affecting subsequent ones.

Birth Intervals↗

PubMed1990

Effects of maternal birth season on birth seasonality in the Canadian population during the seventeenth and eighteenth centuries.

Birth records of the French-Canadian population for the period 1621-1765 were analyzed retrospectively to examine the effect of maternal birth season on the seasonal distribution of births. Preliminary examination indicated that there was a bimodal pattern in birth seasonality: a major peak in early spring, a trough in early summer, a minor peak in autumn, and a trough around December. Because this seasonality was strongly biased at the level of the first birth by the month of marriage, which was concentrated in November, the seasonality of nonfirst births (n = 32,926) was examined in relation to the four seasons of maternal birth. Mothers born in May-July showed a flatter monthly distribution of nonfirst births at a maternal age of 28 years or more. Analysis of marriage-first birth intervals indicated that mothers who married in August-October showed a lower percentage of immediate conception (intervals of 8-10 months), whereas those mothers born in May-July had a higher percentage of immediate conception. This difference in birth seasonality shown by mothers born in May-July is similar to results from early twentieth-century Japan. Some seasonal infertility factors could have affected the embryos at the earliest stage of pregnancy, modifying a part of the seasonal variation in birth rate.

Birth Intervals↗

PubMed1998

Assessing and interpreting birth spacing goals in Costa Rica.

A procedure for assessing birth spacing goals, an important component of fertility preferences, is proposed and applied to 1993 Costa Rican data. Based on a reverse or backward survival analysis, preferred birth intervals are estimated to range between 3.5 and 4.5 years (1.5 years for the interval union to first birth). These intervals are 2 or 3 years shorter than crude estimates from data on open or last closed intervals, which are upwardly biased by selection and left censoring effects. To achieve these spacing preferences, a cohort must spend about two-thirds of the time using contraception (one-third in the interval union to first birth). An inverse association between desired family size and desired birth interval is evident only in parity-specific analyses.

Birth Intervals↗

PubMed1992

Age at last birth and its components.

This paper examines the ways in which the behavior of twentieth century cohorts of American women changed simultaneously in the three components of fertility that determine age at last birth--age at first birth, spacing between subsequent births, and parity progression ratios of subsequent births--to produce changes in the timing of the completion of childbearing. It decomposes changes in the mean age at last birth among cohorts and between whites and nonwhites to changes in these three components. To perform these analyses, we developed and applied a method to estimate the distributions and means of ages and last births, birth intervals, and parity progression ratios from age- and parity-specific fertility rates available from vital statistics data. Results show that the cohorts increased and decreased their age at first birth, birth intervals, and parity progression ratios of lower and higher birth orders in almost every possible combination so as to achieve a relatively young age at final birth.

Birth Intervals↗

PubMed2000

Are births underreported in rural China? Manipulation of statistical records in response to China's population policies.

Under the current family planning policy in China, the criterion for evaluating all parties involved in the birth planning system provides an incentive for everyone to see that the policy is met, either in reality through strict enforcement of family planning regulations, or statistically through manipulation of statistical records. We investigate underreporting of births in four rural counties of northern China, using data from a 1992 sample survey featuring a reproductive history. To clarify the mechanisms of underreporting, we focus on the ways in which reporting errors may affect the distribution of first births by time since marriage. The results of our investigation suggest that in three of the four counties, first-birth intervals are lengthened by underreporting of girl babies and by replacing them with second births reported as first births.

China↗

PubMed1999

Why do cohabiting couples marry? An example of a causal event history approach to interdependent systems.

The purpose of this paper is to demonstrate a causal approach to interdependent systems based on two empirical investigations. These examples demonstrate 1) the study of two highly interdependent processes: entry into first marriage as the dependent process and the process of first birth/first pregnancy as the explaining one; 2) an interdependence occurring mainly in a very specific phase of individuals' lives (i.e., during the period of first family formation); 3) the involvement of time lags between cause and its effect (e.g., time until detection of conception); and 4) the highly dynamic character of an unfolding effect over time (i.e., the effect of first pregnancy/first birth on first marriage strongly depends on the progress of pregnancy and the time since the birth has taken place).

Birth Intervals↗

PubMed1976

Labor force participation and family formation: a study of working mothers.

Drawing upon a sample of 638 mothers aged 18 to 40, with at least some marital work experience, significant associations were found between the extent, kind, and timing of employment and a series of family formation variables. Generally lower fertility, longer first birth intervals, and earlier use of birth control were associated with the longest work durations, the highest status jobs, and work before the birth of the first child. The data failed, however, to differentiate desired family size.

Adolescent↗

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↗

PubMed2001

Waiting for Trivers and Willard: do the rich really favor sons?

Parental investment theory has been put forward as a major evolutionary argument explaining male or female biased birth sex ratio, the Trivers-Willard (T-W) hypothesis, predicting that parents living in good circumstances will bias their investment to sons, whereas parents in poor circumstances will bias their investment toward daughters. Tests of the T-W hypothesis on human beings have shown limited evidence for parents appearing to differentiate their investment to sons or daughters according to the reproductive potential of each sex. The present study tests the T-W hypothesis among a large contemporary Polish sample using first birth interval and extent of breastfeeding as measures of parental investment, and economic status and level of parental education as measures of parental condition. The extents to which parental investment and markers of parental condition vary by sex of the child were examined using log-linear analysis. Weak support for the T-W effect is found among families where fathers were best educated, where a greater proportion of first-born boys are breastfed longer than girls, while the opposite trend is observed among families with fathers with lowest levels of education. Although the present study does not fully support the T-W hypothesis, it gives evidence of greater investment in female offspring at the lower extremes of income, and greater investment in males at higher levels of income.

Adult↗

PubMedDate not supplied

Delayed childbearing in Canada: trends and factors.

"Using period and cohort birth order statistics, an overview of the phenomenon of delayed childbearing in Canada is presented. Data employed in the period analysis were mainly from the years 1944 to 1985, while women born between the years 1935 and 1960 were the subjects of the cohort analysis. An examination of selected indices, namely, age-specific first-birth fertility rates, median ages of women at first-order birth and cumulative first-order birth rates shows that there is an overall trend for women to postpone the initiation of childbearing until late twenties or early thirties.... The results indicate that work experience, education, occupation and year of marriage are important variables influencing age at first birth and first-birth interval." (SUMMARY IN FRE AND ITA)

Age Factors↗

PubMed1998

Marriage season, promptness of successful pregnancy and first-born sex ratio in a historical natural fertility population--evidence for sex-dependent early pregnancy loss?

We investigated population-based vital records of the seventeenth and eighteenth century French Canadian population to assess the effects of marriage season on the outcome of the first births under natural fertility conditions (n = 21,698 marriages). Promptness of the first successful conception after marriage differed according to marriage season; the proportion of marriages with a marriage-first birth interval of 8.0-10.0 months was lowest (34%) for marriages in August-October (P = 0.001). Although the male/female sex ratio of the babies born with an interval of 8.0-10.0 months was generally higher (1.10) than those with an interval of 10.0-24.0 months (1.05), the marriages in August-October resulted in a significantly reduced sex ratio (0.96) among only the prompt conceptions (P = 0.026). We discuss whether this seasonal reduction of the sex ratio could be partly explained by a clustered pregnancy loss of male zygotes in early pregnancy.

Adult↗

PubMed1977

Age at puberty in relation to age at marriage and parenthood: a national longitudinal study.

A longitudinal study of a British cohort has collected information on puberty, judged by menarcheal age for the girls and the pubertal stage of the boys at age 14 3/4. This information has now been related to the ages at which these young people married and became parents. For the young men there was evidence of a direct relationship between degree of sexual maturity at age 14 3/4 and their ages at entry into marriage and fatherhood. For the young women, if pregnancy did not intervene between menarche and marriage, there was evidence of a direct relationship between menarcheal age and marriage age. But there was no evidence that these earlier-maturing young women became mothers at earlier ages than later maturers. This arose through the later-maturing young women having shorter first birth intervals than the earlier maturers. Premarital conceptions were also more prevalent amongst the later maturers.

Aging↗

PubMed1991

Remarks on population planning and control.

We investigate the use of control theory in population planning and show how the use of age at first birth, birth interval, and sex ratio as control variables leads to a practical, fault tolerant approach to population planning and control.

Age Factors↗

PubMed1993

Effect of oxygen and neostigmine on stillbirth and pig viability.

In this experiment, 98 multiparous Yorkshire sows blocked on farrowing date were randomly assigned to four treatments in a 2 x 2 factorial arrangement. Oxygen inhalation (6 L/min) by the sow was tested in an effort to reduce stillbirth rate and improve pig viability. This study also tested the effect of increasing uterine contractions using neostigmine (5 mg) to determine whether simultaneous administration of oxygen to the sow could improve the inconsistent response of stillbirth rate to neostigmine. Pig viability was assessed using viability scoring and blood gas analysis of samples obtained from the suborbital sinus immediately after birth. The farrowings averaged 12.2 pigs/litter, 7.8% stillbirths, and 3.5% low viability (viability score < or = 6) pigs. Treatment had no effect on stillbirth rate or pig viability. Oxygen treatment increased pO2 (P = .0002), increased pCO2 (P = .02), and decreased pH (P = .02) in sow venous blood sampled after the birth of the last pig, but it had no effect on pig venous blood gases. Neostigmine treatment had no effect on either sow or pig venous blood gases. Oxygen treatment doubled the length of the first birth interval after the start of treatment (P = .003) but had no effect on remaining birth intervals. Neostigmine had no effect on birth interval. It is suggested that the effect of oxygen on birth interval is the reason for the lack of improvement in stillbirth rate.

Animals↗

PubMed1983

Female employment and reproductive behavior in Taiwan, 1980.

The impact of female employment on fertility preferences and behavior is examined with data from a 1980 national sample of Taiwanese women. The guiding hypothesis is that the greater the involvement of women in the impersonal market sector, the lower the fertility preferences, the longer the first birth interval, and the lower the actual fertility. Findings reveal that female employment in Taiwan is only weakly related to reproductive behavior. Even with increased participation of women in the modern market sector, female employment apparently has little impact on fertility preferences or behavior. Implications are drawn for policies aimed at lowering fertility.

Adolescent↗