In most cases, breastfeeding can delay menstruation after childbirth, though the length of the period's postponement varies from one mother to the next. In fact, some women do observe menstruation while breastfeeding, as early as six weeks after childbirth. Others do not get a period until their baby turns two years old, as long as they still nurse often. The delay of menstruation while breastfeeding is typically due to the suppression of reproductive hormones, which is why most women do not ovulate until they stop nursing their baby. Those who do menstruate while breastfeeding often notice irregular periods until they wean their child.
The hormone that allows women to breastfeed is prolactin, and as long as the baby is exclusively nursed, the level of prolactin should remain high. This usually results in the suppression of reproductive hormones, which means that ovulation and menstruation are typically kept at bay. Of course, as babies get older, they tend to start sleeping through the night and eating solid foods, which means they nurse less often. This allows prolactin levels to drop, which can lead to ovulation. Thus, a woman who hopes to prevent menstruation while breastfeeding is advised to ensure that her baby gets all its nutritional needs through breast milk only, at least until he or she is six months old.
After about six months, many babies begin eating solid foods, which means that they need fewer nursing sessions. In addition, their stomachs are large enough to allow them to sleep through the night, which means that night feedings are typically not necessary. For this reason, many mothers who begin nursing less frequently may experience menstruation while breastfeeding. While this may not be avoidable after the baby is six months old, as starting solid foods is important, this outcome may be prevented in younger babies. Women who wish to delay menstruation while breastfeeding are often encouraged to feed their baby every few hours, even at night, and also allow their baby to nurse instead of using a pacifier.
Of course, some women still get a period despite breastfeeding, especially if they occasionally supplement with formula, or encourage their baby to sleep through the night. Such women can expect the first few periods to be either lighter or heavier than the flow before they became pregnant. It is also considered common for the period to only come every few months while the mother is still breastfeeding. It should return to normal once the baby is weaned from the breast.