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.
PIP: Between 1983 and 1987 in Baltimore, Maryland, researchers followed 60 breast-feeding mothers (55% single and 82% black) and 22 non breast feeding mothers (3% single and 93% white) for 72 weeks to better understand resumption of postpartum ovarian activity and the impact breast feeding has on resumption of ovarian activity. Laboratory personnel conducted daily urinary assays to detect ovulation and to evaluate the luteal phase. Ovulatory first vaginal bleeding episodes increased with the time (45% in the first 12 weeks to 100% after 49 weeks). 69% of breast-feeding mothers experienced an ovulatory first bleeding episode, but 47% of these cycles had reduced excretion of pregnanediol during the luteal phase, indicating a reduced likelihood of conception before first bleedings. The women's descriptions of perceived characteristics of their bleeding episodes were linked to ovulatory or anovulatory status. Specifically, women who reported regular or heavy bleeding were more likely to have had a preceding ovulation than those who reported spotting or light bleeding (84% vs. 35%; odds ration = 9.8; p .001). Resumption of ovulation was delayed in breast-feeding mothers. All non breast-feeding mothers menstruated within the first 12 weeks postpartum compared with just 20% of breast- feeding mothers. First ovulation occurred on average 45 days after delivery among non breast-feeding mothers and 189 days among breast- feeding mothers. The multivariate analysis revealed that breast-feeding episode contributed greatly and independently to the delay in ovulation (relative risk = .66 and .91, respectively; p .001). The protected effected of breast feeding remained even when mothers supplemented with bottle feeds 92% pregnancy rate over 6 months for both exclusive and partial breast feeders). These results indicated that breast feeding of increased frequency and suckling duration provides considerable protection from pregnancy, even when mothers use supplements.