Breastfeeding has been called “nature’s contraceptive,” and like many birth control methods, when used properly, it is highly effective in preventing pregnancy. Along with the numerous other health benefits of breastfeeding for both mother and infant, breastfeeding can provide safe and effective contraception for up to six months after a baby is born. It is still possible, however, for a nursing mother to become pregnant during this time, but her chances are low if her physiological condition is consistent with the lactational amenorrhea method (LAM) guidelines.
Evidence for the Health Claim
No reversible contraceptive method is perfect. However, studies have shown that the LAM can be up to 98% effective. According to its advocates, when a woman is “fully breastfeeding” and not getting her menstrual period, she has a less than 2% chance of becoming pregnant in the first six months after giving birth. (“Fully breastfeeding” means feeding the baby with only breastmilk—the only exception being 1 or 2 mouthfuls of supplement per day, and permitting no more than 4-6 hours to elapse between nursing). This 2% pregnancy risk compares favorably to using a condom correctly when a woman is not nursing.
Extensive research has been conducted on the LAM method. A review article published in the American Journal of Obstetrics and Gynecology looked at pregnancy rates of women who followed the LAM method in two separate studies conducted in Kenya and Chili. The results showed that the rate of unplanned pregnancy was less than 1% during the first six months after giving birth.
Further research indicates that longer and more intensive breastfeeding may result in even more extended infertility—beyond the six-month period specified by LAM. However, to stay on the safe side, the LAM guidelines are intentionally conservative and encourage women to use alternative methods of contraception—barrier methods are most highly recommended—after six months (when supplemental feedings become more common).
Evidence Against the Health Claim
LAM advocates emphasize that their method is 98% effective only if the guidelines are followed correctly. Breastfeeding should not be viewed as foolproof under any circumstances. It is not hard to find a woman with closely spaced children who reports becoming pregnant while still breastfeeding. If a nursing mother does not breastfeed her child exclusively (for example, starts the infant on formula or solid food), or stops nursing at night, she may begin to ovulate and could get pregnant even if her menstrual periods haven't started yet.
Zealous breastfeeding is likely, but not guaranteed, to prevent pregnancy. The LAM method was first endorsed in 1988 at the Bellagio Consensus Meeting on “Breastfeeding as a Family Planning Method” by a group of international lactation experts. LAM is especially useful in countries where family planning and contraception are not widely available for financial or religious reasons. LAM may also be attractive to women who are hesitant to begin taking hormonal medication (birth control pills) while nursing. However, it is important to keep in mind that once a woman stops following the LAM guidelines—for example, starts feeding her infant formula and solid foods, thus decreasing the regularity of suckling—reproductive hormones begin to be released again and the likelihood of becoming pregnant rapidly increases.