Depot medroxyprogesterone acetate and basal serum prolactin levels in lactating women

OBJECTIVE: To study the effect of depot medroxyprogesterone acetate on basal serum prolactin levels in lactating women. METHODS: We compared basal serum prolactin levels in 25 lactating women after depot medroxyprogesterone acetate injection and in 25 lactating women of similar age who were using a copper T380A intrauterine device (control group). This sample size was required in order to have 95% power to detect a significant difference. Basal prolactin levels were evaluated by time-resolved fluoroimmunoassay three times (6 weeks postpartum and 3 and 6 weeks after beginning either contraceptive method). RESULTS: At 6 weeks postpartum, before beginning either contraceptive method, the mean prolactin levels in the study and control groups were 991.31 and 948.75 mU/L, respectively (P =.850, 95% confidence interval [CI] -407.57, 492.70). Three weeks later, the mean prolactin levels in the study and control groups were 1156.12 and 860.10 mU/L, respectively (P =.116, 95% CI -76.20, 668.26). At the last follow-up, the mean prolactin levels in the study and control groups were 1127.83 and 710.97 mU/L, respectively (P =.026, 95% CI 51.97, 781.73). There were no significant within-group differences at 6 weeks postpartum before contraception and at 6 weeks after beginning contraception in the study and control groups (P >.05, 95% CI -327.99, 243.02 and -46.76, 522.33, respectively). CONCLUSION: Contraception with depot medroxyprogesterone acetate in lactating women produced higher basal prolactin levels than contraception with copper T380A intrauterine device.