Is breastfeeding while pregnant safe during pregnancy?

What does the evidence say about breastfeeding while pregnant during pregnancy?

1. An Italian perinatal-medicine position paper found no evidence that healthy women who breastfeed during pregnancy have higher miscarriage or preterm-delivery risk and did not support routine discouragement. It advised caution when preterm-delivery risk is already present because evidence in that group is limited. 1
2. A U.S. observational analysis of 10,661 pregnancies found an adjusted association between exclusive breastfeeding during pregnancy and miscarriage, while complementary breastfeeding showed no increased risk. Self-reported exposure and residual differences between families mean the result cannot establish causation. 2
3. A 2025 meta-analysis found no significant overall differences in miscarriage, preterm labor, birth weight, or broad pregnancy complications, but did report associations with low birth weight and fetal growth restriction. Country setting affected subgroup results, and the underlying studies were heterogeneous. 3
4. A 2023 systematic review of 10 studies found breastfeeding during pregnancy generally unrelated to pregnancy outcome or miscarriage but emphasized caution in high-risk pregnancy and the higher nutritional demands of simultaneous pregnancy and lactation. 4
5. A physiologic study followed milk from only two women during early pregnancy and found compositional changes consistent with reduced mammary secretory activity despite continued suckling. The tiny sample supports the possibility of supply change but cannot predict when or how much milk will fall for an individual. 5

Is breastfeeding while pregnant safe in each trimester?

• First trimester. First-trimester breast and nipple tenderness can make nursing uncomfortable. Review bleeding, pain, prior losses, preterm-birth history, the nursling's reliance on milk, and maternal nutrition with the prenatal and pediatric teams before deciding whether to continue, reduce feeds, or wean.
• Second trimester. Milk secretion and composition may change as pregnancy hormones rise. Watch the breastfeeding child's swallowing, food and fluid intake, wet diapers when age-appropriate, and growth rather than assuming every change requires weaning.
• Third trimester. Evidence does not show that nursing routinely starts labor in a low-risk pregnancy, but data are limited. A twin or otherwise high-risk pregnancy, poor fetal growth, bleeding, regular contractions, or threatened preterm birth warrants direct obstetric guidance about continued nursing.