Characteristics and determinants of postpartum ovarian function in women in the United States

Objective: Our aim was to characterize the influence of breast-feeding on the postpartum return of ovarian activity for the purpose of assessing the relevance of the lactational amenorrhea method of contraception for women in the United States. Study design: Twenty-two non-breast-feeding and 60 breast-feeding women from Baltimore collected daily urine specimens that were assayed to determine ovulation and luteal phase adequacy. Vaginal bleeding was ascertained weekly, and breast-feeding women recorded infant feeding daily. Proportional-hazards models were used to relate measures of breast-feeding to the occurrence of ovulation. Results: Two thirds of women ovulated before their first vaginal bleeding, but 47% of those cycles had decreased luteal-phase pregnanediol excretion. Breast-feeding frequency and suckling duration were significant predictors of the risk of ovulation (p < 0.001). Supplementation with bottle feeding was associated with a reduction in breast-feeding. Conclusion: A high degree of protection from pregnancy can be achieved using breast-feeding frequency and suckling duration, even with supplemented breast-feeding.