Simple as that answer appears, nursing during pregnancy presents issues to consider for a healthy and happy pregnancy. There is no evidence that nursing during pregnancy will cause a miscarriage. When a newborn begins breastfeeding, the suckling stimulates release of the hormone oxytocin into the mother's bloodstream.
Experts maintain that oxytocin has much less effect on the uterus during pregnancy.
Unless your pregnancy is term or the cervix is ripe, the released oxytocin stimulation is not sufficient to bring on labor. A diet higher in calories and protein-rich foods is necessary because of extra energy needed to support pregnancy and breastfeeding. Choosing unprocessed foods to meet the caloric requirement is recommended. After the first few months of pregnancy, the mother's milk supply may naturally reduce. The nursing infant may also experience a change in the taste of milk during mother's pregnancy and weaning may occur at this time.