Hormonal effects in newborns occur because in the womb, babies are exposed to many chemicals (hormones) that are in the mother's bloodstream. After birth, the infants are no longer exposed to these hormones. This exposure may cause temporary conditions in a newborn.
Hormones from the mother (maternal hormones) are some of the chemicals that pass through the placenta into the baby's blood during pregnancy. These hormones can affect the baby.
For example, pregnant women produce high levels of the hormone estrogen. This causes breast enlargement in the mother. By the third day after birth, breast swelling may also be seen in newborn boys and girls. Such newborn breast swelling does not last, but it is a common concern among new parents.
The breast swelling should go away by the second week after birth as the hormones leave the newborn's body. DO NOT squeeze or massage the newborn's breasts because this can cause an infection under the skin (abscess).
Hormones from the mother may also cause some fluid to leak from the infant's nipples. This is called witch's milk. It is common and most often goes away within 2 weeks.
Newborn girls may also have temporary changes in the vaginal area.
These changes are common and should slowly go away over the first 2 months of life.
Reviewed By: Neil K. Kaneshiro, MD, MHA, Clinical Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.