I'm a lactation consultant, and I want you to know that full strength estrogen hormonal birth control pills will cause a decrease in your milk supply. Some mothers have done well on the mini-pill (progesterone only), but other mothers experience a drop in milk supply with that pill, too. As others have suggested, any kind of barrier method (condoms, diaphragm, even spermicidal foams or the non-hormonal IUD) are safest. Research has shown that if a mother is breastfeeding exclusively day and night, meeting nearly all her baby's sucking needs at the breast; that is, not giving bottles at all or even pacifiers and NOT encouraging the baby to sleep through the night or allow finger/thumb sucking, she will be 98% protected from another pregnancy for the first 6 months IF she has NOT had a period. In other words, only 2% of women nursing like that will get pregnant before their first period. (Can't tell you who is in that 2%, though.) Whenever your first period returns, then it is over, and fertility is back! If you still have not had your first period after 6 months, the protection drops to 95%. In our culture, most women are giving occasional bottles and pacifiers, and are encouraging the baby not to nurse during the night, and therefore are at risk for an earlier return of their menstrual cycles and fertility. So the old wive's tale that you can't get pregnant while breastfeeding does have some basis in fact, but only so long as the above conditions are met.