This paper investigates the effects of continued breast-feeding after resumption of menses on fertility, using data from two retrospective surveys in India and single decrement life table and multivariate time-dependent hazards analyses. Breast-feeding even after the return of menses is found to be associated with longer birth intervals. The interaction of breast-feeding duration after resumption of menses and postpartum amenorrhoea has a significant effect on the risk of conception after return of menses.

Children's intelligence increased in the United States by approxi-mately 3 IQ points per decade over the period 1932–78. New evidence shows that these increases have been sustained during the last 20 years. Two recent studies indicate that the rates of increase for 1972–89 and 1978–89 were 3·3 and 3·5 IQ points per decade respectively.

This study examines the extent of assortative mating for education in Northern Sudan and urban Khartoum. More males than females were found at higher levels of education. Increasingly, people tend to marry persons of equal educational level, but the unequal educational opportunities for males and females have led to the emergence of educational exogamy in which members of different educational levels are more likely to marry from the adjacent educational category than from distant categories. The increasing level of education for both sexes, and especially for females, may in part explain the rising trend in age at marriage.

This study examines fertility differentials by religious affiliation in Liberia, within the context of two competing hypotheses: the characteristic and particularised theology. Using a subsample of currently married women from the 1986 Liberian Demographic and Health Survey, the study examines the fertility of five religious groups: Catholic, Protestant, Moslem, traditional, and other women. Overall, the findings are more consistent with the characteristic hypothesis, because the small fertility differentials by religious affiliation are largely accounted for by differences in the socioeconomic and demographic characteristics of these women.

Variation in the duration and pattern of breast-feeding contributes significantly to inter-population differences in fertility. In this paper, measures of suckling frequency and intensity are used to compare the effects of breastfeeding practices on the duration of lactational amenorrhoea, and on the length of the birth interval in three prospective studies undertaken during the 1980s, among Quechua Indians of Peru, Turkana nomads of Kenya, and Gainj of Papua New Guinea.

In all three societies, lactation is prolonged well into the second year postpartum, and frequent, on-demand breast-feeding is the norm. However, the duration of lactational amenorrhoea and the length of birth intervals vary considerably. Breast-feeding patterns among Gainj and Turkana are similar, but Turkana women resume menses some 3 months earlier than do the Gainj. The average birth interval among the Gainj exceeds that of nomadic Turkana by over 15 months. Suckling activity decreases significantly with increasing age of nurslings among both Gainj and Quechua, but not among Turkana. Earlier resumption of menses among Turkana women may be linked to the unpredictable demands of the pastoral system, which increase day-to-day variation in the number of periods of on-demand breast-feeding, although not in suckling patterns. This effect is independent of the age of infants.

The short birth intervals of Turkana women, relative to those of the Gainj, may be related to early supplementation of Turkana nurslings with butterfat and animals' milk, which reduces energetic demands on lactating women at risk of negative energy balance.

The relationships between 29 cephalic and post-cephalic body dimensions and the length and regularity of the menstrual cycle, as well as the duration of menstrual bleeding, have been investigated in 327 Austrian women. Five of the eight head measurements and seventeen of the 21 body measurements correlated statistically significantly with the individual menstrual variables. Measures of facial and post-cephalic robustness and the amount of subcutaneous fat tissue correlated negatively with the length of cycle, as well as with the difference between minimum and maximum cycle length, a measure of the cycle regularity. The post-cephalic height and length dimensions correlated significantly positively with bleeding duration. The results indicated a marked influence of body type, especially the amount of subcutaneous fat, on the length and regularity of the menstrual cycle.

This study uses sets of historical family reconstitutions from all of Quebec and from four villages of the Haut-Jura, France—first marriages of 2226 and 994 women, respectively—to investigate the physiological and social factors affecting age of mother at last birth before and during fertility transition. Age remained high throughout the period covered in Quebec, under ‘natural’ conditions, but showed a steady decline in the French material which extends to late 19th century generations practising family limitation.

Age at marriage had no influence in Quebec; in France, however, women with the most surviving children at age 35 continued childbearing the latest. There was no link between biological ability to achieve a live birth, or in health status or aging rhythm, and age at last birth. Behaviour of mothers and daughters showed no relation. The variability in age at last birth thus appears to be random under natural conditions; with the onset of controls, social differences seem to influence not only the end of childbearing, but all aspects of behaviour governing final family size and child survival.

Onset of capacity for childbearing in women is dated biologically by menarche, although actual onset may be delayed. The end of childbearing is less understood but recent demographic and biological research on fertility at older ages is clarifying the end of fertility.

The demographic view of declining fertility with age is based on age-specific fertility in natural fertility populations, artificial insemination and pregnancy rates by age and World Fertility Survey data. New data from the Demographic and Health Surveys on exposure to the risk of pregnancy shows that whereas older women biologically need longer exposure to pregnancy, exposure declines on behavioural grounds such as duration of marriage. Actual fecundity is obscured by factors of fecundability. Recent research on medically assisted conception is adding to the understanding of declining fecundity with age, especially the relative contributions of endometrial and ovarian ageing.

This paper reviews the available information on declining fertility with age and discusses the implications of the extension of fertility through new medical technologies.

Duration of postpartum amenorrhoea (PPA) was compared among women who breast-fed For ≥ 6 months (breast-feeding group) Or ≤ 3 Months (formula-feeding group) and was found to be significantly shorter among the latter. associations between maternal factors and duration of PPA were examined. within the formula-feeding group, the only variable associated with duration of PPA was duration of breast-feeding. among breast-feeding mothers who resumed menstruation after 3 months postpartum, duration of PPA was positively associated with parity and negatively associated with maternal body mass index (bmi) at 3 months postpartum. Among breastfeeding mothers who resumed menstruation after 6 months, duration of PPA was positively associated with parity, pregnancy weight gain, number of night feeds and milk volume at 6 months, and negatively associated with maternal age and bmi at 6 months postpartum. These results indicate that maternal anthropometric status is related to duration of PPA, even in a relatively well-nourished population of lactating women.

A biosocial model of the effects of early adolescent testosterone levels and religiosity on adolescent males' sexual attitudes and activity over a 3-year period was examined. Using panel data for approximately 100 boys who were 12·5/13·0 years old at study entry, significant additive effects of free testosterone and frequency of attendance at religious services were demonstrated on the transition to first intercourse and other aspects of sexual behaviour and attitudes. No interactive effects of the two predictors were found. Boys with higher free testosterone levels at study entry who never or infrequently attended religious services were the most sexually active and had the most permissive attitudes. Boys with lower free testosterone who attended services once a week or more were the least active and reported the least permissive attitudes. For some behaviours, differences between free testosterone/attendance groups increased over time, resulting in substantial behavioural differences by the final round of measurement 3 years later.

Factors affecting desired family size in rural Bangladesh are examined using data from contraceptive prevalence surveys conducted between 1983 and 1991. The analysis suggests that mothers having two sons and one daughter are more inclined to perceive their family as complete than those having three sons and no daughter. Logistic regression analysis indicates that important determinants of desire for more children are age of woman, current contraceptive use status, work status, and family planning worker's visit. The policy implications of these findings are discussed.

Data on patterns of consanguineous marriage were collected from 5340 families resident in eight cities in the Pakistan province of Punjab. To assess whether social and/or occupational class was interacting with con-sanguinity, information also was obtained on the hereditary qaum to which each family belonged. In the present generation 46·5% of all marriages were contracted at the level of second cousin or closer, with an average coefficient of inbreeding (F) of 0·0286, and the results indicated that in each of the seventeen qaums there was strong preference for marriage to a close biological relative. However, significant differences existed in the distribution of consanguineous marriage by qaum membership, which could interfere with the interpretation of studies into the biological effects of inbreeding.

The traditional preference for sons may be the main hindrance to India's current population policy of two children per family. In this study, the effects of various sociodemographic covariates, particularly sex preference, on the length of the third birth interval are examined for the scheduled caste population in Assam, India. Life table and hazards regression techniques are applied to retrospective sample data. The analysis shows that couples having two surviving sons are less likely to have a third child than those without a surviving son and those with only one surviving son. Age at first marriage, length of preceding birth intervals, age of mother, and household income have strong effects on the length of the third birth interval.

A comparison of contraceptive and fertility data for 1985–91 with data for 1983 shows that fertility has continued to decline in Bangladesh, in all segments of society. The magnitude of decline varied according to educational level, region and urban–rural locality. The percentage decline in total marital fertility rate was somewhat higher among urban than rural residents; educated women showed greater declines than uneducated, increas-ing the overall educational differences in total fertility by 1991. Factors contributing to the recent decline in fertility are discussed.

According to the 1991/92 Tanzania Demographic and Health Survey, a Tanzanian woman has, on average, 6·1 births before she reaches age 50, a decline of about one birth per woman since the early 1980s. The major proximate determinant of fertility is universal and prolonged breastfeeding. An analysis of the social and demographic correlates of fertility shows that infant and child mortality, level of education and age at first marriage are among the factors which significantly influence fertility in Tanzania.

Neonatal death (mainly due to tetanus) was common in St Kilda until 1891. Two aspects of this phenomenon are studied; factors which pre-dicted death, and the impact of neonatal death on family building. Maternal age appeared to be a predictive factor for death of the first child, but only in children of high birth order were other factors, particularly the number of previous neonatal deaths, important. The first birth interval appeared to be determined mainly by the date of the first birth, independent of neonatal mortality levels. For later intervals, the neonatal death of the previous child appeared to be the main determining factor.

The variability of three behavioural risk factors for heart disease—heavy alcohol and tobacco consumption and physical inactivity—was assessed in an Australian Aboriginal community, where heart disease death rates were high. Prevalence levels were assessed by comparison with those experienced by all adult Australians and by evaluating whether Aboriginal rates were influenced by underlying sociodemographic conditions. Relative risk ratios, odds ratios and logistic regression analysis were used.

A total of 159 males and 114 females participated. Compared to all Australians, Aborigines are significantly more likely to drink five or more drinks on a drinking day, to be current smokers, and not to participate in vigorous exercise. In the Aboriginal community, univariate analysis indicates that: the odds of being a heavy drinker are significantly higher for those in unsatisfactory health; odds of being a current smoker are significantly higher for those in unsatisfactory health or unemployed; odds of not participating in vigorous exercise are significantly higher for those in unsatisfactory health, unemployed or without secondary education. Multivariate analysis shows that risk of being a heavy drinker is independently associated with sex, age, and health status; risk of being a current smoker is associated with health and employment status. The risk of not participating in vigorous exercise is significantly related to all sociodemographic variables examined. Reasons for these associations are discussed.

The evidence from gynaecologists in Northern Ireland shows confusion in interpretation and practice of abortion law, with some women even being denied abortion after rape. Over two-thirds of gynaecologists supported a change in the law which would leave the abortion decision to the woman and her doctor, but less than half wanted the introduction of the British law.

Demographic data on fertility and intermarriage are useful measures of integration and assimilation. This paper reviews trends in total fertility and intermarriage of foreign populations in Europe and compares them with the trends in fertility of the host population and the sending country. In almost all cases fertility has declined. The fertility of most European immigrant populations and of some West Indian and non-Muslim Asian populations has declined to a period level at or below that of the host society. Muslim populations from Turkey, North Africa and South Asia have shown the least decline. Intermarriage is proceeding faster than might be expected in immigrant populations which seemed in economic terms to be imperfectly integrated. Up to 40% of West Indians born in the UK, for example, appear to have white partners as do high proportions of young Maghrebians in France.

This study examines the effects of birth order and interpregnancy interval on birthweight, gestational age, weight-for-gestational age, infant length, and weight-for-length in a sample of 2063 births from a longitudinal study in the Philippines. First births are the most disadvantaged of any birth order/spacing group. The risks associated with short intervals (<6 months) and high birth order (fifth or higher) are confined to infants who have both attributes; there is no excess risk associated with short previous intervals among lower-order infants, nor for high birth order infants conceived after longer intervals. This pattern is observed for all five birth outcomes and neonatal mortality, and persists in models that control for mother's age, education, smoking, family health history and nutritional status. Since fewer than 2% of births are both short interval and high birth order, the potential reduction in the incidence of low birthweight or neonatal mortality from avoiding this category of high-risk births is quite small (1–2%).