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In this paper information collected in the World Fertility Survey on durations of breastfeeding and postpartum abstinence and amenorrhoea is used. Rates of conception and of resumption of menstruation are presented for four breastfeeding states: full breastfeeding, partial breastfeeding, weaned, and never breastfed. The various patterns of breastfeeding affect resumption of menstruation in consistent and expected directions. Continued breastfeeding beyond the resumption of menstruation and of sexual relations exerts a considerable contraceptive effect in all twelve countries considered, although interesting differences also emerge. The consequences of these findings are discussed. [ABSTRACT FROM AUTHOR]

Fecundability - the monthly probability of conception - incorporates both physiological and behavioural elements that vary across a woman's reproductive life span. How much of the variation in fecundability during the reproductive period can be attributed to age- related changes in physiology, and how much to variation in coital frequency? We use a mathematical model of fecundability to consider this question. Intra-uterine mortality has an important effect on fecundability: effective fecundability (the likelihood of a conception that results in a live birth) is less than half of total fecundability (the likelihood of any conception) at nearly all ages when coital frequency is held constant. The change in effective fecundability with increasing coital frequency is non-linear: it declines with increasing frequency. At all coital frequencies, the effects of increasing physiological age are greatest at the youngest and oldest reproductive ages, while between the ages of 20 and 30 physiological change has only a small impact on effective fecundability. [ABSTRACT FROM AUTHOR]