Smoothed breastfeeding durations and waiting time to conception.

Breastfeeding beyond the resumption of mother's menstruation plays a significant role in the proximate determinants of fertility. Breastfeeding and postpartum amenorrhoea data collected from retrospective surveys usually exhibit digit preferences. Here, these heaping errors were smoothed by B-spline and used in multivariate models of risk of conception to investigate the contraceptive effect of breastfeeding. The data used come from a 1987 Indian survey. Results show that lactation, after mother's menses resume, reduces the risk of conception. Heaping in breastfeeding data attenuates this relationship. When adjustment is made, breastfeeding reduced the rate of conception by 47 per cent; the reduction, with adjusted data, was 63 per cent.