Fertility regulation in nursing women: V. Long-term influence of a low-dose combined oral contraceptive initiated at day 90 postpartum upon lactation and infant growth.

The study was designed to test the long-term influence of a low-dose oral contraceptive upon lactation and infant growth when treatment was initiated at day 90 postpartum. The contraceptive tested contained ethinyl estradiol 0.03 mg and levonorgestrel 0.15 mg. The control group was formed by women who chose non-hormonal contraception at the same postpartum time. Only cases who were in exclusive breast-feeding with a minimal infant daily weight increase of 20 g per day during the third month of age were included. The oral contraceptive group showed a significantly lower percentage of cases in full nursing from the 6th postpartum month and a significantly lower infant weight increase during the 4th month of age when compared to the control group. No differences were found in the absolute infant weight up to one year of age. No adverse side effects upon infant's health were detected. It was concluded that the oral contraceptive tested showed a moderate inhibitory influence upon lactation when treatment was initiated at day 90 postpartum.