The reliability of menses to indicate the return of ovulation in breastfeeding women in Manila, The Philippines.

Demographic studies generally use menses to indicate the return of fertility during breastfeeding. In a prospective study of 40 breastfeeding women in Manila, the resumption of ovarian activity was monitored by urinary hormone assays, and menstrual status was determined by weekly interview. For the women who menstruated before six months postpartum, first menses was not a good indicator of ovulation because there was a high proportion of anovular menses (67 percent), and the lag between anovular first menses and subsequent ovulation was 15.7 (+/- 4.4) weeks. After six months postpartum the proportion of anovular first menses declined to 22 percent, and the lag between anovular first menses and ovulation was 7.3 (+/- 4.6) weeks. If all anovular and ovulatory menstrual episodes are considered, the mean interval between first observed menses and first ovulation was 8.4 weeks during the first six months postpartum and only 0.1 week after six months. Thus, in breastfeeding women, menses is an inaccurate proxy measure for the timing of fertility return before six months postpartum, but a good indicator of the resumption of ovulation after six months.

Risk of ovulation during lactation.

60 breastfeeding mothers in Baltimore and 41 in Manila recorded their infant feeding patterns daily, and gave additional information at weekly interviews. Ovarian activity was monitored by assays for hormone metabolites in daily urine samples. On average, women in Baltimore breastfed less often but for longer at each feed than women in Manila, and the mean times until ovulation were 27 and 38 weeks post partum. 41% of first ovulations had luteal phase defects. Anovular first menses were common (45.1%) during the first 6 months post partum but the rate fell greatly thereafter. The risk of ovulation was reduced by a higher frequency of breastfeeds, longer duration of each feed, and less supplementary feeding. During the first 6 months post partum, amenorrhoeic women had low risks of ovulation (below 10%) with partial breastfeeding, and exclusive breastfeeding reduced the risk to 1-5% with either frequent short feeds or infrequent longer feeds. However, if the woman started menstruating before 6 months post partum, or if she continued breastfeeding beyond 6 months, the risk of ovulation rose, and contraception would be needed.

PIP: The factors predicting the return of ovulation during lactation were investigated in 60 breast feeding mothers from Baltimore, Maryland, and 41 mothers from Manila, the Philippines. The women in Manila breast fed more frequently (11.0 mean daily feeds) than those in Baltimore (5.8 feeds) throughout the first postpartum year. However, during the first 6 months, the average length of an individual breast feed was longer among US women. Although both groups gave few supplementary feeds during the first 20 weeks after delivery, more non-bottle feeds were given thereafter in Manila. Use of bottle feeds was similar in both groups. Women who first ovulated before 6 months gave significantly fewer mean daily breast feeds during this period (8.5) than those who first ovulated after this point (10.7). Women who first ovulated before 6 months also had a lower percentage breast feeds of total feeds (84.2%) than women who first ovulated later (88.2%). The mean duration of amenorrhea was 25.3 weeks in Baltimore and 31.7 weeks in Manila; the average times before first ovulation were 27.0 weeks and 38.0 weeks, respectively. Multivariate analyses showed that the length of suckling per feed, the daily number of breast feeds, and the proportion of breast feeds were all significantly and independently associated with a low risk of ovulation. Up to 6 months postpartum, exclusive breast feeding reduced the risk of ovulation by 98-99% during amenorrhea and by 94-97% after anovular menstruation. Only amenorrheic women practicing exclusive breast feeding during the first 6 postpartum months can achieve a pregnancy rate below 2%. These findings suggest that contraceptive use is indicated among women who resume menstruating before 6 postpartum months or continue breast feeding beyond 6 months.