Effects of hormonal and nonhormonal contraceptives on lactation and incidence of pregnancy.

From June 1974 to June 1976, 665 women who had given birth to full-term infants and who were willing to nurse the infant were admitted to this study. At three to six weeks postpartum, subjects chose which of four study groups to join. One-hundred-forty-three mothers chose Group I, exclusive lactation with no contraception; 109 chose Group II, lactation and intrauterine contraception (IUD); 228 chose Group III, lactation and an intramuscular injection of 150 mg medroxyprogesterone acetate (Depo-Provera Sterile Aqueous Suspension, DMPA) given every three months; and 185 chose Group IV, lactation and one tablet of 0.6 mg Clogestone Acetate given daily. Mother and child were examined monthly until the child's spontaneous weaning, the mother's dropout, or the study's close in 1979. Mothers from Group I (exclusive lactation) were dropped from study when they requested and were prescribed a contraceptive. During the first six months of study, the percent of mothers who dropped out of Groups I, II, III, and IV for personal or medical reasons was 28.0, 16.5, 11.4, and 27.1, respectively. Pregnancies began to occur in the sixth month postpartum. Overall, pregnancies occurred in 6% of mothers in exclusive lactation, 3% of mothers protected by an IUD, and 8% of mothers protected by Clogestone. No pregnancies occurred in the 228 women receiving DMPA. Some mothers in the Clogestone or DMPA groups were still breast-feeding their children two or three times a day at the study's close, at which time the child was three or more years of age. No ill effects were observed in growth and development of these children during the study. The DMPA group had the most mothers who were breast-feeding for more than 20 months.