I have known a woman or two who got pregnant while breast-feeding their infants. Nobody, except their husbands, was more surprised than they were to find that out!

It is very uncommon in the early months after giving birth and exclusively breast-feeding to get pregnant. Everything is working against normal fertility--the baby nursing frequently causes prolactin secretion, which inhibits normal menstruation, and due to the high intensity of the baby's needs, sexual activity is often not high on the list. But that is only when the infant is nursing frequently, as in every four hours or less.

Once a baby nurses less frequently, or the mother supplements with bottles, or the baby sleeps through the night, all bets are off. Normal hormonal cycles can return, and so can fertility. That is true even before a normal period occurs.

Women who have had babies will never forget how they bled for weeks post-delivery. The uterus needs time to return to normal, and it goes through a process of decreasing blood supply and cleaning. That process can wax and wane, and it can seem like a period returned during that time. Some women then start counting on the calendar til the next period is expected. That can be the flaw that leads to a very rapid next baby.

Unless you use some form of birth control, you could become pregnant even though you're breast-feeding. Depending on the rhythm method is a poor choice at this time because all the normal indicators will be off for a while. Cervical mucus may not return to normal until after a few cycles, and even menstruation may be nothing more than spotting while breast-feeding.

The key here is to know that pregnancy can happen while breast-feeding once your infant nurses less often, especially when the baby goes more than four hours between feedings. While mothers often brag about how their baby sleeps through the night, that bragging should be tempered with the realization that birth control methods have to begin again, too. Unless, of course, you don't mind having "Irish twins."