We have recorded the duration of lactational anovulation and amenorrhoea in a well-nourished group of Australian women who breastfed their babies throughout the study. The data enabled us to compare the theoretical cumulative probability of conception among breastfeeding women who had unprotected intercourse irrespective of their menstrual status with that of those who had unprotected intercourse only during lactational amenorrhoea. Breastfeeding alone is not an effective form of contraception, since all the women in our study resumed normal ovulation while still breastfeeding. However, among women who have unprotected intercourse only during lactational amenorrhoea but adopt other contraceptive measures when they resume menstruation, only 1.7% would have become pregnant during the first 6 months of amenorrhoea, only 7% after 12 months, and only 13% after 24 months. Thus for our women it would be possible to extend the Bellagio Consensus Conference guidelines which stated that lactational amenorrhoea can only be relied on as a contraceptive for the first 6 months post-partum in women who are fully or almost fully breastfeeding. The lactational amenorrhoea method can be relied on for excellent contraceptive protection in the first 6 months of breastfeeding, irrespective of when supplements are introduced into the baby's diet; for women who continue to breastfeed the method can also give good protection for up to 12 months post partum. Once menstruation has returned, other forms of contraception are essential to prevent pregnancy.
PIP: The Bellagio Consensus Conference on breast feeding as a family planning method determined that a mother who is breast feeding and remains amenorrheic has a 98% rate of protection from pregnancy for 6 months postpartum. A prospective study of the duration of lactational anovulation and amenorrhea was conducted by recruiting 101 breast- feeding women before their infants were 6 weeks old. Salivary progesterone (2-4 times a week) and in a subgroup urinary estrogen and pregnanediol excretion rates 1 mg/24 hours indicated ovulation) were determined to check ovarian activity. The mean duration of amenorrhea was 9.5 months in 101 women, and anovulation lasted 10.6 months in 89 women. The mean age of infants was 5.3 months at the start of supplementary feeding. The probability of pregnancy was less than 3 months for 50% of nonlactating women, and 6 months for 85%. In contrast, the probability was 12 months postpartum for 50% of breast- feeding women. Thus, breast feeding was not a reliable form of contraception. Only 1.7% of breast-feeding women using contraception were likely to get pregnant by 6 months, 7% by 12 months, and 13% by the end of 2 years. The results were calculated from the incidence of potentially fertile ovulations prior to the 1st menses over 2-month (1- 12 months) or 3-month (13-24 months) intervals by proportional hazards modeling. In this sample of well-nourished women longer breast feeding could induce prolonged lactational amenorrhea with a major contraceptive effect for up to 12 months or more even after supplements were introduced. The lactational amenorrhea method is appropriate for women in traditional societies who tend to breast feed longer. It helps attain a 2-year birth interval, reduces the risk of maternal breast cancer, and the risk of gastrointestinal infections in infants.