Showing papers by "Kenneth L. Campbell published in 1985"

Demographic and endocrinological aspects of low natural fertility in Highland New Guinea.

Abstract: The Gainj of highland Papua New Guinea do not use contraception but have a total fertility rate of only 4.3 live births/woman 1 of the lowest ever recorded in a natural fertility setting. Reproductive and marital histories were obtained from 305 females and 206 males aged 10+. Each subject was asked about: number of live born offspring ever produced; number of stillbirths ever produced; number and names of offspring currently being nursed; number of current and past spouses; and the cause of dissolution of all past marriages. Blood samples were drawn from 172 volunteer female subjects aged 10-60 years and ovarian function was classified by concentration of progesterone. From an analysis of these cross-sectional demographic and endocrinological data the causes of low reproductive output have been identified in women of this population as: late menarche and marriage a long interval between marriage and 1st birth a high probability of widowhood at later reproductive ages low effective fecundability and prolonged lactational amenorrhea. These are combined with near-universal marriage and a low prevalence of primary sterility similar to that found in other populations. Of all the factors limiting fertility by far the most important are those involved in birth spacing especially lactational amenorrhea. The effects of widowhood on Gainj fertility are negligible. Factors acting to lower fertility fall into 2 categories: those that determine the age of onset of reproduction and those that act to space births. Given the observed pattern of birth spacing however the delay in commencement of reproduction represents on average no more than 1 or 2 live births averted/woman. In contrast were age at 1st reproduction held constant while reducing birth intervals to a mean of 2.0-2.5 years total fertility would increase to about 7 or 8. Future research on natural fertility should focus on specific behavioral and physiological mechanisms governing the reproductive process.

Lactation and birth spacing in highland New Guinea.

Abstract: The effects of infant suckling patterns on the post-partum resumption of ovulation and on birth spacing are investigated among the Gainj of highland New Guinea. Based on hormonal evidence the median duration of lactational anovulation is 20.4 months accounting for about 75% of the median interval between live birth and next successful conception (i.e. resulting in live birth). Throughout lactation suckling episodes are short and frequent the interval changing slowly over time from 24 minutes in newborns to 80 minutes in 3-year olds. Maternal serum prolactin concentrations decline in parallel with the changes in suckling patterns approaching the level observed in non-nursing women by about 24 months postpartum. A path analysis indicates that the interval between suckling episodes is the principal determinant of maternal prolactin concentration with time since parturition affecting prolactin secretion only in so far as it affects suckling frequency. The extremely prolonged contraceptive effect of breastfeeding in this population thus appears to be due to 1) a slow decline in suckling frequency with time since parturition; and 2) absence of a decline over time in hypothalamic-pituitary responsiveness to the suckling stimulus. (authors modified)