Hypertrophy of the breast tissue in the newborn is sometimes wrongly called Gynecomastia (which is a term used to describe an enlargement of the breast tissue in boys only). This is a very common phenomenon that can be found in around 70% of babies. The reason for this enlargement is a high estrogen levels passing to the baby while he was in the womb.
Read more of benigh hypertrophy of the breast tissue in the newborn as well as of mastitis.