Sonographic Features of Physiologic Neonatal Breast Enlargement
n engl j med 360;14 nejm.org april 2, 2009 1445 A n 8-day-old girl presented with bilateral breast enlargement. She was born at term; the 1-minute and 5-minute Apgar scores were 8 and 9, respectively. She was feeding well and showed no signs of discomfort or irritability. Examination of the chest revealed enlarged breast tissue with no evidence of tenderness or discharge. The mother noted that the breasts were slightly swollen at birth and continued to grow larger during the subsequent days. Neonatal breast enlargement is a normal response to falling levels of maternal estrogen at the end of pregnancy, which trigger the release of prolactin from the newborn’s pituitary. Neonatal breast enlargement is common (seen in approximately 70% of neonates) and is independent of the sex of the baby. It usually occurs in the first week of life and resolves within a few weeks, as was the case with this patient. The enlarged breast may discharge liquid; this usually resolves without treatment over a period of a few weeks. Squeezing the breast to facilitate the discharge may lead to irritation, further enlargement, the persistence of the hypertrophied tissue, or, in rare cases, infection (mastitis or abscess).