Breastfeeding While Pregnant
Though breastfeeding suppresses fertility in most women, at some point you may become pregnant while nursing. There have been plenty of studies done on breastfeeding while pregnant which confirm that in most cases there is no medical reason to wean. Nursing will not deprive the fetus of nutrients. Studies done in developed countries found that the babies of mothers who breastfed while pregnant were born healthy and at appropriate weights. Women who are not gaining the expected amount of weight may need to consume extra calories. The nursing baby will not be harmed either. A baby who is not ready for solids will probably need to be supplemented as your milk supply decreases. Many babies wean themselves during pregnancy as a result of the change in the taste of the milk, or a decrease in the milk supply. Another point that causes concern is the oxytocin rush that occurs during nursing.
The role of oxytocin
Oxytocin causes milk to flow and the uterus to contract. These contractions are only effective when labor is imminent. If there is no reason to believe that labor could begin prematurely, there is no need to stop nursing. Oxytocin has the same affect on the uterus during orgasm. If your doctor has not counseled you to avoid sexual relations during your pregnancy than breastfeeding is fine too.
Many women choose to stop nursing during pregnancy for other reasons, such as sore nipples during the first trimester or difficulty finding a comfortable position as your stomach grows. Some women continue throughout the pregnancy and nurse both the toddler and the new baby after the birth. This is called tandem nursing. If you would rather not tandem nurse, begin weaning your nursing child early in the pregnancy, in order to wean him gradually but with enough time that he will be completely weaned well before the birth of his new sibling.