Pregnancy outcome and the time required for next conception

Abstract Variations in the time required for next conception by outcome ofthe preceding pregnancy, and the age of woman, are studied for Taiwanese women. Pregnancy interval, defined as the period between the end of one pregnancy and the beginning of the next, is taken as a measure of the time required for the next conception. The averages and variances of pregnancy intervals are estimated from reports of pregnancies occurring in a probability sample of 2,443 married women, aged 20-39, living in Taichung (Taiwan) in 1962. The effects of 'truncation bias' and 'memory bias' on the two moments of pregnancy intervals are estimated indirectly by cross-classifying women according to their ages at interview and their ages at the beginning (or end) of each pregnancy interval. The moments of post-partum amenorrhoea are, then, estimated indirectly from the moments of pregnancy intervals. The effects of truncation bias and memory bias are compensatory in this sample. In the absence of contraception, women, on an average, took longer to conceive following a live birth than following a foetal death. The time taken for next conception increases as women become older irrespective of the outcome of the preceding pregnancy.     

The cocos-keeling islands: A demographic laboratory

The Cocos Islands, which are situated in the Indian Ocean approximately halfway between Colombo and Fremantle, were first peopled early in the nineteenth century and were gradually developed as a very isolated coconut plantation with a labour force consisting partly of persons of Malay stock descended from the original group of settlers and partly of Bantamese contract labourers from Java. As the Cocos-born population increased in size, the dependence on contract labour decreased and, before the end of the century, all immigration ceased. The 1947 Malay population of the islands was about 1,800.

The islands are fascinating from a demographer's point of view because there was a virtually complete registration of live births, deaths and marriages and a partial registration of stillbirths. With these registration records it was possible to construct the life history of every individual from birth, through infancy and childhood to marriage, and thence through fatherhood or motherhood to death.

The picture revealed by an analysis of these records is that of a population with very high fertility and with mortality at a high level before the first World war and at a medium level after that war. Crude birth rates varied between 50 and 60 per thousand population during the period 1888 to 1947. Crude death rates were between 30 and 40 per thousand population until 1912 but under 2.0 per thousand population after 1918.

Most Cocos girls married before reaching the age of 20 and there were an average of between eight and nine live births per woman living through the childbearing period. There was a steady decline in the average number of live births with advancing age at marriage from age 16 onwards. A significantly high proportion of those dying in the middle of the childbearing period had never married, but the fertility of those marrying at an early age (14, 15 and 16) and dying before reaching the age of 36 was slightly higher than that of those who married at a similar age and survived. Women who survived to the age of 55 were of higher fertility than those who died between the ages of 40 and 55. An analysis of birth intervals revealed significant differences (a) between birth intervals after a stillbirth or after a live birth in which the child died in early infancy, and birth intervals after a live birth in which the offspring survived for longer than 0.4 years, and (b) between the interval from first to second birth and the subsequent birth intervals. There was a difference of almost exactly a year between the average birth interval after a stillbirth or live birth ending in a neo-natal death and the average birth interval after the birth of a child surviving to age 2; there was a similar difference of a year between corresponding median birth intervals.

From 1888 to 1912 infant mortality was well above 300 per thousand. After 1918 infant mortality averaged rather under 100 infant deaths per 1,000 live births. The reduction in infant mortality rates was accompanied by an increase in the mortality of children aged 1 to 4, and the heavy incidence of mortality at these ages after 1918 is the most striking feature of the analysis of mortality by age. Whilst mortality in infancy fell much more heavily on males than on females, early childhood mortality was much higher in Cocos for girls than for boys. The life table computed for the period 1918 to 1947 indicated a life expectancy of about 50 years for males and 47 years for females.     

Prospective study of birth interval dynamics in rural Bangladesh

Abstract A group of 209 married, fecund women in rural Bangladesh were studied prospectively for 24 months from 1969 to 1971 to define some of the biological and sociological factors relating to fertility performance. These women were selected from a larger study population of 112,000 that had been followed with a daily house-to-house vital registration programme since 1966. The selected women were interviewed bi-weekly and were asked questions about menstruation, pregnancy, lactation, husband's occupational absences, and monthly urine tests for pregnancy were taken. The results for 193 non-contracepting women revealed that the seasonal pattern of births previously observed in this population could be associated with a corresponding seasonal pattern of conceptions and that this was due to a seasonal trend in fecundability. The highest conception rates were in the coolest months of the year. Post-partum lactational amenorrhoea was very prolonged, averaging 17 months for women with a surviving child. The appearance of the first post-partum menstrual flow (onset of ovulation) also had a seasonal trend which could not be adequately explained. The median waiting time to conception, once menstruation had resumed was eight months. This interval was influenced by seasonal fluctuations, as well as by the age of women and by husbands' absences. The foetal wastage rate was 15·0 per 100 conceptions, with 62 per cent of the foetal losses occurring during the second month of gestation. Overall, the average birth interval was 33 months, with the prolonged lactational amenorrhoea accounting for almost 45 per cent of this interval. From the Department of Population Dynamics, Johns Hopkins University, School of Hygiene and Public Health, Baltimore, Maryland 21205.     

Prospective study of birth interval dynamics in rural Bangladesh

A group of 209 married, fecund women in rural Bangladesh were studied prospectively for 24 months from 1969 to 1971 to define some of the biological and sociological factors relating to fertility performance. These women were selected from a larger study population of 112,000 that had been followed with a daily house-to-house vital registration programme since 1966. The selected women were interviewed bi-weekly and were asked questions about menstruation, pregnancy, lactation, husband's occupational absences, and monthly urine tests for pregnancy were taken. The results for 193 non-contracepting women revealed that the seasonal pattern of births previously observed in this population could be associated with a corresponding seasonal pattern of conceptions and that this was due to a seasonal trend in fecundability. The highest conception rates were in the coolest months of the year. Post-partum lactational amenorrhoea was very prolonged, averaging 17 months for women with a surviving child. The appearance of the first post-partum menstrual flow (onset of ovulation) also had a seasonal trend which could not be adequately explained. The median waiting time to conception, once menstruation had resumed was eight months. This interval was influenced by seasonal fluctuations, as well as by the age of women and by husbands' absences. The foetal wastage rate was 15·0 per 100 conceptions, with 62 per cent of the foetal losses occurring during the second month of gestation. Overall, the average birth interval was 33 months, with the prolonged lactational amenorrhoea accounting for almost 45 per cent of this interval.      

The effects of pregnancy spacing on infant and child mortality in Matlab, Bangladesh: how they vary by the type of pregnancy outcome that began the interval

Using high-quality longitudinal data on 125,720 singleton live births in Matlab, Bangladesh, we assessed the effects of duration of intervals between pregnancy outcomes on infant and child mortality and how these effects vary over subperiods of infancy and childhood and by the type of outcome that began the interval. Controlling for other correlates of infant and child mortality, we find that shorter intervals are associated with higher mortality. Interval effects are greater if the interval began with a live birth than with another pregnancy outcome. In the first week of the child's life, the effects of short intervals are greater if the sibling born at the beginning of the interval died; after the first month, the effects are greater if that sibling was still alive. Many relationships found are consistent with the maternal depletion hypothesis, and some with sibling competition. Some appear to be due to correlated risks among births to the same mother.     

Some aspects of the relationship between the levels of infant mortality and fertility in the ESCAP region

The death of a child within the first year of life is a crucial factor in fertility decisions in a developing country. The infant mortality rate gives a close, inverse indication of the socioeconomic conditions of a country. This paper presents studies by Brass, Rutherford, Chowdhury, Khan and Chen, Agrawal, Iskander and Jones, in summary/abstract form. It concludes that the probabilities of survival are poorer for births of older women and/or higher parities. Early child deaths may increase the total period of exposure to the risk of conception. A lower infant and child mortality norm calls for fewer births to meet the needs for survivors. Child replacement motivational response seems to be strongest with the birth immediately following a death event. Agrawal analyzed the interval between successive births of 1107 women of Patna, Pakistan, according to the age of mother and sex and fate of the previous child. He observed that if a child died shortly after its birth, often a new pregnancy began within a short interval. The interval between 2 consecutive live births when the previous child was male and alive was greater than when the previous child was female and alive. The interval between 2 births was reduced if the child died in infancy and specially if this was a male child.     

Proximate determinants of Philippine fertility: 1983 levels and patterns

Data from the 1983 National Demographic Survey are used to analyze the proximate determinants of Philippine fertility in each of the 3 stages of family formation and to identify all of the direct and indirect factors affecting fertility levels and trends. 10,843 ever-married women and 12,771 children were included. The analysis pertains first to the starting patterns of family formation, the age at first birth, and the proximate determinants (age at menarche, age at first marriage/union, conception before first birth, fetal wastage first birth, interval between first marriage and first birth). Further analysis examines birth spacing patterns including the postpartum nonsusceptible period, the exposure interval and stopping patterns. Almost all births occur within marriage, and childbearing begins late at 22.5 years. However, 15.4% of first births are conceived premaritally. The mean age at first birth increases from younger to older cohorts. Urban women were slightly older (23.0 years) at the birth of their first child. Those with education below the 4th grade had first births 3.5 years earlier. Contraceptive use was low at 1.8% before first birth. Younger cohorts were more likely to use birth control and urban wives were more likely to use it than rural wives. 6.4% reported a first pregnancy ending in nonlive births, which were primarily spontaneous abortions (5.2%), stillbirths (1.0%), and induced abortions (.2%). 5.8% report never having been pregnant and 1.1% never having given birth to a live-born child. 20.4% were childless between the ages of 15-24 years, and 4.6% between 25-34 years. Childlessness was slightly higher among urban women (7.1%) than rural women (6.7%). A decreasing age at menarche has appeared; i.e., 13.6 years for the cohort 15-24 years, and 14.0 for the oldest cohort. By age 15, 82.9% had begun menstruating. The mean age at marriage is early at 20.7 years, and older cohorts tended to marry later at 21.4 years. Urban women marry a year later (21.4 years) than rural women. Lower educated women marry 4 years earlier. The mean length between first marriage and first birth was 18.4 months. In the younger cohorts, spacing patterns are shorter. Postpartum susceptibility is short. Return to sexual relations after a birth occurred at 2.8 months. The exposure time required to conceive is fairly long at 16.6 months and is attributed to contraceptive use, since coital frequency is high and temporary separation is infrequent. The average age at last birth is late at 37.6 years.     

Comment on 'facts and artifacts in the study of intra-uterine mortality: a reconsideration from pregnancy histories' by henri léridon(1)

Abstract Extract I have suggested that at a given birth order the probability of having a further pregnancy is greater when the last pregnancy had been spontaneously aborted than when it resulted in a birth.(2) Léridon,(3)in the course of a valuable paper on foetal wastage, presents data which, according to him, impugn my suggestion. I would like to question his claim.     

A note on nursing practices in an American isolate with a high birth rate

Abstract An unusually short interval between successive births in a non-contracepting and breast-feeding population has been reported by Dr. Mindel C. Sheps (Pop. Studies, 19, 1). Nursing practices that might affect the interval between birth and pregnancy are reported here from systematic observations made in the field. Probable factors are: (1) a maternal diet high in calories and in protein; (2) although infants are nursed for many months, each nursing period is short in a busy and highly patterned community schedule; and (3) supplementary feeding is introduced at an early age.     

On some probability distributions for forward birth interval

Statisticians from Varanasi, India have proposed 2 mathematical models for forward birth interval which are more realistic than past models. For example, past models have assumed fecundability to be constant throughout a woman's reproductive life. On the other hand, the proposed models assume fecundability changes with parity. Further the statisticians use all types of marital durations making their models usable even for short marriage durations. The 1st model uses a parity specific model to develop a model for forward birth interval regarless of parity. The statisticians also include moments of the 1st and 2nd models as expressed for the rth order raw movement of these models to estimate some of their parameters. These models can be used to conduct prospective surveys of family planning programs since birth intervals can best evaluate the effect of these programs. These models have not yet been advanced enough to follow women over a fixed period, however. They only observe women until the last woman conceives. The statisticians do not apply the models to parity specific data because they were not available. Yet they do run the models with parities 0 and 1. The models reveal that the mean length of forward birth interval is strongly influenced by the conception rate which the woman has at the time of the survey. Thus, if women with a certain parity in a community begin an effective family planning method on the survey day, which in effect would reduce the prevailing conception rate, that method would significantly postpone the next live birth.     

The impact of childhood mortality on Fertility in six rural Thanas of Bangladesh

In this article, we examine the relationship between child mortality and subsequent fertility using prospective longitudinal data on births and childhood deaths occurring to nearly 8000 Bangladeshi mothers observed over the 1982-1993 period, a time of rapid fertility decline. Generalized hazard-regression analyses are employed to assess the effect of infant and child mortality on the hazard of conception, with controls for birth order and maternal age and educational attainment. Results show that childhood mortality reduces the time to subsequent conception if the death occurs within a given interval, representing the combined effect of biological and volitional replacement. The time to conception is also reduced if a childhood death occurs during a prior birth interval, a finding that signifies an effect of volitional replacement of the child that died. Moreover, mortality effects in prior birth intervals are consistent with hypothesized insurance (or hoarding) effects. Interaction of replacement with elapsed time suggests that the volitional impact of child mortality increases as the demographic transition progresses. This volitional effect interacts with sex of index child. Investigation of higher-order interactions suggests that this gender-replacement effect has not changed over time.     

Cohort Trends in Premarital First Births: What Role for the Retreat From Marriage?

We examine cohort trends in premarital first births for U.S. women born between 1920 and 1964. The rise in premarital first births is often argued to be a consequence of the retreat from marriage, with later ages at first marriage resulting in more years of exposure to the risk of a premarital first birth. However, cohort trends in premarital first births may also reflect trends in premarital sexual activity, premarital conceptions, and how premarital conceptions are resolved. We decompose observed cohort trends in premarital first births into components reflecting cohort trends in (1) the age-specific risk of a premarital conception taken to term; (2) the age-specific risk of first marriages not preceded by such a conception, which will influence women’s years of exposure to the risk of a premarital conception; and (3) whether a premarital conception is resolved by entering a first marriage before the resulting first birth (a “shotgun marriage”). For women born between 1920–1924 and 1945–1949, increases in premarital first births were primarily attributable to increases in premarital conceptions. For women born between 1945–1949 and 1960–1964, increases in premarital first births were primarily attributable to declines in responding to premarital conceptions by marrying before the birth. Trends in premarital first births were affected only modestly by the retreat from marriages not preceded by conceptions—a finding that holds for both whites and blacks. These results cast doubt on hypotheses concerning “marriageable” men and instead suggest that increases in premarital first births resulted initially from increases in premarital sex and then later from decreases in responding to a conception by marrying before a first birth.     

Pregnancy termination intervals in a rural area of Bangladesh

Pregnancy termination intervals, i.e., live birth to live birth (LB-LB), live birth to fetal loss (LB-FL), and fetal loss to live birth (FL-LB), are analyzed prospectively between 1966 and 1970 in a rural population (117,000) of Bangladesh. Results indicate that the mean LB-LB interval was almost 30 months, the LB-FL interval 27 months, and the FL-LB interval 18 months. In addition, postpartum amenorrhea was estimated to be about 13-14 months, and the time added by a fetal loss toa LB-LB interval about 15 months. No relationship was found between LB-LB intervals and the number of living or dead children.     

Nonreporting of births or nonreporting of pregnancies? Some evidence from four rural counties in North China

Coale and Banister argue that in China, elevated sex ratios in retrospective surveys are in part a function of collecting birth histories in a culture in which the definition of a birth may exclude mortality shortly after birth: an infant death in the West may be a stillbirth in east Asia. I present data from a recent sample survey featuring a retrospective pregnancy history. These data reveal that at least in the first pregnancy, from which the preponderance of sample births arise, there is no evidence of elevated female infant mortality or of high numbers of stillbirths, but that reported sex ratios are unusually high. The proportion of stillbirths grows for later pregnancies, but not enough to account for high sex ratios. Retrospective fertility data regarding recall over a recent interval are vexed less by a misunderstanding of what a live birth is than by a “misunderstanding” of what a (reportable) pregnancy is.     

A probability model applicable to the study of inter-live birth intervals and random segments of the same

Abstract This paper deals with an analytical study of two types of birth intervals, viz. 'closed intervals' and 'open intervals' through the application of simple probability theory. The 'closed interval' stands for the time interval between two successive live births of a woman, and the 'open interval' denotes the interval between the date of last live birth and the date of survey for a married woman in the reproductive age group surveyed at a point of time. The study considers the 'closed interval' as the sum of independent random variables, each representing a particular component like post-partum amenorrhea, waiting time in the susceptible state, etc. Approximations to the patterns of distributions of these component random variables are made from the available data collected in fertility surveys at Gandhigram. The 'open interval' for any parity is studied separately for two different (mutually exclusive) categories of women, viz. those who have at least one more live birth at some time or other during their reproductive period and those who cease childbearing. In the first case the 'open interval' is considered as a random segment or partition of the corresponding 'closed interval'; in the second as a random segment of the interval between the date of birth of the last child and date at which the woman attains 45 years of age. The mean and variance of the 'open interval' is obtained separately in each case, and the moments of the 'open interval' distribution for women chosen at random from the population are obtained as an appropriate mixture of the two types.     

Use of a fertility simulation model to refine measurement techniques

A stochastic model involving the recurrent events (births, foetal deaths, etc.) associated with human reproduction is defined. Its simulation by means of a Monte Carlo program is described. The model is used to investigate the role of chance in producing biases in certain demographic measurements, particularly as regards the estimation of sterility, foetal death and stillbirth ratios, and birth intervals.     

A new estimate of permanent sterility by age: sterility defined as the inability to conceive

The proportion of couples permanently sterile beyond a certain age is an important component of the reproductive process. Unless medical assistance is used, this age is the upper bound of the fecund period. Most estimates of sterility by age of the woman have been derived from natural fertility populations, in which the number of births and the timing of the last birth (of the complete reproductive history) were not controlled by the couples. Because data on these populations do not include pregnancies not ending in a live birth, the sterility estimates apply to the proportion of couples unable to conceive and to have a live birth. For this reason, it is useful to have an estimate of sterility based on the risk of conceiving, independently of the fate of the pregnancy. Using this new estimate, sterility increases with age much more slowly than with most previous estimates.     

Family planning's benefits include improved child health and nutrition: new data from Bangladesh

2 recent studies from the Matlab in Bangladesh confirm that family planning promotes child survival. The 1st study is a longitudinal analysis of 3370 births in 1985 to women living in 70 villages who were served by the International Centre for Diarrhoeal Disease Research, Bangladesh's Matlab Family Planning and Health Services Project. The 2nd is a study of 12-26 month old children and 24-36 month old children, all of whom were born in the same 70 villages between July 1985 and June 1986. The 1st study demonstrates that family planning improves child survival by lengthening the birth interval. In fact, if women delay a subsequent birth by about 2 years, child survival improves at all ages up to 5 years. Longer birth intervals result in a reduction of very high order births. The same study also reveals that family planning improves child survival indirectly by granting mothers access to integrated maternal and child health services. The 2nd study indicates that a child is 3 times more likely to suffer malnutrition, even at age 3, than a child whose mother gives birth again at an interval greater than 24 months. Specifically, the mother removes the index child from the breast prematurely, thereby adversely affecting the index child's nutrition. The birth interval prior to the index child does not adversely affect the index child's nutritional status, however. The 2nd study's result suggest that birth spacing, as promoted by family planning programs, improves child health and nutrition. The findings from these studies show the importance of continued investments in family planning programs in developing countries.     

Pathways to a Stable Union? Pregnancy and Childbearing Among Cohabiting and Married Couples

This study analyzes the stability of cohabiting and marital unions following a first birth. But unlike previous research, it compares the subsequent trajectories of unions that began with a pregnancy to those in which conceptions came after coresidence. The U.S. data from the 2006–2010 and 2011–2013 cross-sectional files of the National Survey of Family Growth indicate that roughly 1-in-5 first births were associated with rapid transitions from conception into either cohabitation or marriage. Moving in together following a pregnancy—especially an unintended one—is unlikely to lead to marital success or union stability. Compared with marital unions, dissolution rates following birth were particularly high for couples who entered a cohabiting union following conception. Only a small minority of these couples married (i.e., less than one-third), and these marriages experienced high dissolution rates. The results also suggest that the most committed cohabiting couples got married after finding themselves pregnant, leaving behind the most dissolution-prone cohabiting couples. The American family system is being transformed by newly emerging patterns of fertility among cohabiting couples.