Attenuation of Nursing-Related Ovarian Suppression and High Fertility in Well-Nourished, Intensively Breast-Feeding Amele Women of Lowland Papua New Guinea

Carol M. Worthman, Carol L. Jenkins, Joy F. Stallings and Daina Lai

Journal of Biosocial Science (1993) 25, 425–443

By error, an incorrect version of Fig. 2 was published in this article, on p. 433. It should be replaced by the correct diagram, as given below.

Intense, sustained nursing lengthens inter-birth intervals and is causally linked with low natural fertility. However, in traditional settings, the effects of such nursing on fertility are difficult to disentangle from those of nutrition. Results from an prospective, direct observational study of reproductive function in well-nourished Amele women who nurse intensively and persistently but who also have high fertility are here presented. Endocrine measures show that ovarian activity resumes by median 11·0 months postpartum. Median duration of postpartum amenorrhoea is 11·3 months, time to next conception is 19·0 months, and the inter-birth interval is 28·0 months. Average life time fertility is 6·8. High fertility in Amele women is due both to refractoriness of reproductive function to suckling stimuli, and to maintenance of equivalent age-specific fertility rates across the reproductive life span.

The 1984–85 Pakistan Contraceptive Prevalence Survey showed that urban wives had more than twice the literacy rate of rural wives. The present study explored the relationship of the rural–urban gap in female literacy to differences in contraceptive use. In rural areas, literacy did not increase women's perceptions of having reached a ‘sufficient’ number of living children, although the opposite was true for urban areas. Yet rural women with an ‘insufficient’ number of living children were more likely to use contraception if they were literate, as did their urban counterparts. Thus, raising the literacy rate in rural Pakistan would not narrow the rural–urban gap in contraception to cease childbearing but would narrow the rural–urban gap in contraception used to space wanted births further apart. Recommendations for government policy are made.

The effects of family sex composition on fertility preferences and behaviour during the period 1977–88 are examined using longitudinal data from Matlab, Bangladesh. The sex composition of living children was found to be systematically related to fertility preferences and behaviour, with a higher number of sons at each family size associated with a higher percentage of women wanting no more children, a higher percentage currently using contraception, and lower subsequent fertility. However, the highest percentage wanting no more children, using contraception and having lowest subsequent fertility was found among women who already had one daughter as well as at least one son. The effects of sex preference on fertility preferences and behaviour were measured using an index developed by Arnold (1985). The results suggest that while sex preference remained largely unchanged during the study period, its effect on contraceptive use declined and its impact on actual fertility remained modest and fairly stable.

The associations of social and behavioural factors on preterm birth in Singapore were studied using hospital maternity records of 20,723 consecutive singleton births between January 1986 and November 1991. The overall proportion of preterm births was 3·6%, the rates for the Chinese, Malay and Indian groups being 3·2%, 3·8% and 4·9% respectively. Teenage mothers were at a higher risk of preterm labour compared to women aged 20–29 years. The incidence of preterm labour decreased with increasing educational status. Preterm births were six times more likely in women who had no antenatal care. Women who had three or more previous births were at a higher risk, while those who had one or two previous births were at a lower risk compared to women who had none.

Re-examination of the polygyny–fertility hypothesis, by multiple regression analysis of the 1988 Ghana DHS data, reveals that polygyny has no effect on the number of children ever born; i.e. polygynously married women are as fertile as those monogamously married. Husband's age has no significant role in determining the number of children ever born to a woman.

This study indicates that urban marital patterns in nine Nigerian cities influence fertility. Fertility is also influenced by age at marriage, region of residence, ethnicity and religion; education and employment lead to marriage delay and tend to conflict with childbearing by enhancing the status of women.

The effects of low income, urbanisation and young age population on age-adjusted rates of first marriage, divorce and live birth among the Japanese population in 46 prefectures were analysed by stepwise regression for 1970 and for 1975. During this period, Japanese society experienced a drastic change from long-lasting economic growth to serious recession in 1973. In both 1970 and 1975, the first marriage rate for females was inversely related to low income and the divorce rates for both males and females were positively related to low income. The live birth rate was significantly related to low income, urbanisation and young age population only in 1975. The first marriage rate for females and the divorce rates for both sexes increased significantly but the first marriage rate for males and live birth rate significantly decreased between 1970 and 1975. These findings suggest that low income was the essential factor affecting first marriage for females and divorce for males and females.

Two samples of births were used to examine the effect of son preference and population policy on sex ratios in Hebei and Shaanxi provinces of China. The results from all births to women aged 15–49 in the 1985 In-Depth Fertility Survey indicated a strong son preference but no clear policy impact on sex ratios at different birth orders. In a sample of selected births during 1975–84 to women aged 40 or under, the mixed influences of son preference and population policy were clearly reflected in the high and rising overall ratios at birth, and the increasing sex ratios with parity. Possible explanations for these findings are discussed.

In a sample of 311 couples from the Afroamerican community of Bluefields, Eastern Nicaragua, the distribution of matrimonial distance shows a deviation from the leptokurtic rule. This results from assortative mating among the population.

Data from the final 16 years of a 28-year ongoing survey of menarcheal age are reported. From 1971 onwards, recalled aged at menarche was recorded for all young women entering the University of Warwick. These data show that mean menarcheal age is increasing, a trend which is independent of father's occupation, family size, position of girl in the family, and physique. This continues a similar upward tendency noted in a preceding study in Swansea. It appears that the downward trend to earlier age at menarche of the earlier decades of this century has been replaced by one in the opposite direction.

The link between socioeconomic status and health has long been recognised. This study of deaths among Australian men aged 15–59 years demonstrates that during the 20-year period, 1966–86 the number of premature deaths was dramatically reduced among all socioeconomic groups, primarily as a result of falls in death rates due to heart disease, stroke and trauma. However, the marked differences in death rates according to social class remain, to the extent that if men of all social classes had the same mortality experiences as professional and technical workers the overall death rates for Australian men would be reduced by 60%. Socioeconomic status is the most important indicator of health status among Australians.

The rate of consanguineous mating in north Jordan was 63·7% with an average inbreeding coefficient of 0·0283. First cousin marriages were the most predominant type (58·5%); villagers showed higher levels than city dwellers. The level of female education did not influence consanguinity rate.

Sex differences are reported for samples of approximately 1000 16-year-old blacks, Indians and whites in South Africa on ten tests of cognitive ability. Males obtained significantly higher means on non-verbal reasoning, spatial and mechanical aptitude, and females obtained significantly higher means on perceptual speed and memory for meaning (except among the black sample). In general the sex differences in South Africa are consistent with those typically obtained in the United States.