Lactation and fertility.

Breastfeeding suppresses ovarian activity resulting in amenorrhea and infertility. The frequency of breastfeeds and their duration appear to be important in maintaining amenorrhea--and night-time sucking appears to be particularly crucial. Supplementary feeding may affect fertility by altering suckling behaviour, but the evidence is confusing as to whether feeding supplements reduces the duration of amenorrhea and increases the risk of conception. Mothers who are better nourished tend to have a shorter period of amenorrhea than the malnourished, possibly because the infant has to suckle for a shorter period to obtain the nourishment needed. Lactation has an important effect on fertility at the population level. However, it cannot be considered a reliable contraceptive at an individual level.