Effect of progestin-only pill on pituitary–ovarian axis activity during lactation

Abstract

We have monitored effects of progestin-only pill (POP) on ovarian activity during breastfeeding. Twenty-one women, using barrier methods (BM) of contraception and 9 women on POP were enrolled 6 weeks postpartum (PP) and followed-up to 18 weeks PP. There was little change in plasma follicle-stimulating hormone and luteinizing hormone, and no differences between BM and POP. POP did not affect plasma estradiol. There was no difference between BM and POP in plasma inhibin B concentrations. The size of follicles was similar in both groups in all time points. There was an increase in the endometrial thickness from 6 weeks PP to 18 weeks PP in BM (3.7 ± 0.5 vs. 5.4 ± 0.6 mm, p < 0.05), but no differences within the POP group or between the treatment groups. POP does not suppress gonadotropins nor affect growth of ovarian follicles during breastfeeding. Thus, the contraceptive effect of POP is likely mediated through local actions at the endometrium and cervix in a manner similar to that in menstruating women.