Survival-time analysis of the postpartum anovulatory interval as measured by rise in urinary pregnanediol-3-glucuronide in lactating women

This was a prospective, observational study of women living in the USA and belonging to an organization that teaches ecological breast-feeding. One hundred forty-four fully lactating mothers (recruited through a newsletter advertisement) began the study and eighty-nine completed it. Subjects electronically recorded daytime and nighttime nursing data and fertility signs, and collected morning urine samples. We hypothesized that lactational style would be highly predictive of both the month-specific rate of postpartum ovarian recrudescence as ascertained by urinary metabolite analysis of ovarian steroids and that postpartum menses would be coupled with the first rise in urinary pregnanediol-3-glucuronide (PdG). PdG levels three times greater than baseline level suggested that ovulation had occurred. Survival analysis clarified the effect of breast-feeding behavior on the postpartum anovulatory and amenorrheic intervals. First postpartum menses and first detected PdG rise were highly coupled. A Cox proportional hazards model indicated a statistically significant decrease in the probability of resuming ovulation if suckling sessions are closely-spaced. The style of lactation, including specific behaviors, was significantly associated with extended postpartum infertility.