Background: Despite widespread cultural vilification, lactationY pregnancy overlap remains common. Its actual adverse effects remain uncertain.
　　Purpose: This study compared rates of success in reaching full-term delivery and newborn birth weights between two groups of multiparous pregnant women: those who breastfed during pregnancy and those who did not.
　　Methods: This was a comparative study conducted over 9 months, which examined two groups of women in the maternity units of two hospitals in Birjand, Iran. The first group comprised 80 women who breast-fed for 30 days or more during pregnancy; the second group comprised 240 women who did not. The two groups had similar distributions in terms of maternal age, parity, medical/midwifery problems, and nutritional changes during pregnancy. Two trained nurses used a self-developed questionnaire to collect data.
　　Results: Results found no significant difference in full-term or non-full-term births rates and mean newborn birth weight between the two groups. We further found no significant difference between full-term or non-full-term births and mean newborn birth weight for those who continued and discontinued breastfeeding during pregnancy in the overlap group.
　　Conclusions/Implications for Practice: Results suggest that breastfeeding during normal pregnancy does not increase chance of untoward maternal and newborn outcomes. Nurses and midwives should give expectant mothers appropriate evidence-based guidance and focus attention on promoting proper nutritional intake based on lactation status during pregnancy.