The mother facing the decision of whether to wean or continue nursing during her pregnancy often has mixed emotions, and may get conflicting advice from friends, family, and health care providers.

The most common concern is whether continuing to breastfeed will put the expected baby at risk in some way. There is no evidence to suggest that nursing while pregnant endangers the fetus during a normal pregnancy. If a mother has previously delivered a premature baby, develops signs of pre-term labor, or is carrying multiples, there is concern that a hormone released during lactation (oxytocin) may stimulate contractions and trigger a premature labor. In these special situations, mothers are often advised to wean their older child. Research suggests that the uterus is not receptive to hormonal stimulation from oxytocin until around 24 weeks gestation, so it is generally safe to consider nursing until about 20 weeks, even in these special situations. There is almost never a need to wean abruptly during pregnancy.
The mother who is deciding whether to continue nursing during her pregnancy has several factors to consider: her medical history, her physical and emotional comfort level, the nursing child's age, and his need to nurse. If the pregnancy is progressing normally, then the decision of whether to continue to breastfeed is more an individual 'parenting' decision rather than a 'medical' decision. Medical reasons for weaning include uterine pain or bleeding, a history of premature delivery, or a prolonged weight loss during the course of the pregnancy.

There is no evidence that nursing during a pregnancy will cause miscarriage during the early months. Miscarriage occurs spontaneously in about 16-30 percent of all pregnancies, so it will sometimes happen while a mother is nursing. The nursing mother should not add the burden of guilt to the pain of losing a baby to miscarriage.

Nursing during pregnancy will not deprive the fetus of essential nutrients, and will not create a harmful "drain" on the mother's body. During pregnancy, it is always important to eat nutritiously, gain weight appropriately, and get adequate rest. A well-nourished mother should have no problem providing enough nutrients for both her unborn baby and her nursing child. Breastfeeding provides several opportunities each day for the expectant mother to take breaks and rest while her toddler nurses or naps.

Due to hormonal changes, most mothers will experience some degree of nipple soreness during pregnancy, which can make nursing very uncomfortable. Nipple soreness is the most common reason given for weaning during pregnancy. The soreness usually is most pronounced during the early months, and lessens somewhat as the pregnancy progresses. Since the cause of the soreness is hormonal, there is no real treatment other than time. Some mothers find relief by reducing the time the baby spends at the breast, limiting nursing sessions to nap and bed-time, and others find that reminding the toddler to "open wide" while latching on may reduce soreness.

During pregnancy, most mothers' milk supply will decrease due to hormonal changes. During the second trimester, the milk will begin to change to colostrum. Both the quantity and the taste of the milk change dramatically during this time, and many older babies will wean themselves when the milk changes. Don't worry that the toddler will "use up" all the colostrum, because this doesn't happen. Your body will make all the colostrum your newborn baby needs when he is born.
If you are nursing a baby younger than six months when you become pregnant, you will need to carefully monitor his growth and weight gain, and supplemental feedings may be necessary. Older babies who are eating solids will usually show an increased appetite for other foods as your milk supply decreases.

Many mothers experience a kind of restlessness or irritation with the older baby when he nurses during her pregnancy. If you want to continue nursing in spite of this "antsy" feeling, try distraction techniques, such as reading a book, watching television, deep breathing, or listening to relaxing music.

Although many babies wean themselves during their mother's pregnancy, there is no guarantee that they will not want to start nursing again once the new baby is born. If you don't want to start nursing again, try offering the big brother or sister a taste of your milk in a cup. This usually satisfies their curiosity.

Some mothers decide to continue nursing their older baby all through their pregnancy and then nurse both babies after the newborn arrives. This is called "tandem nursing", and while it's not the right choice for everyone, it can be a very joyful experience. It can also be stressful, so the decision to tandem nurse should be made only after careful consideration of the practical issues involved as well as the emotional ones.