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. Proportion-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.