Neonatal Breast Hypertrophy

September 14, 2005
Robert P. Blereau, MD

The bilateral breast hypertrophy seen on a 12-day-old boy's chest began 4 days earlier. This anomaly results from elevated levels of maternal circulating estrogen in late gestation that crosses the placenta and stimulates the baby's breasts. Both sexes are affected equally.

The bilateral breast hypertrophy seen on a 12-day-old boy's chest began 4 days earlier. This anomaly results from elevated levels of maternal circulating estrogen in late gestation that crosses the placenta and stimulates the baby's breasts. Both sexes are affected equally.

"Witches' milk," a nipple discharge, may be associated with breast hypertrophy. Manipulation of the swollen breast can cause irritation and further swelling. One breast may hypertrophy several days before the other. When this occurs, consider acute mastitis, which requires antistaphylococcal antibiotic therapy.

An infant's breasts usually return to normal size within several months to about 1 year. Parental reassurance is the only treatment necessary.