Maternal hormones (hormones from the mother) are some of the chemicals that pass through the placenta during pregnancy and affect the fetus.

For example, during pregnancy there are high levels of the hormone estrogen. This hormone causes breast enlargement in the mother. It can have a similar affect in newborn boys and girls by the third day after birth. Such newborn breast swelling is temporary, but is a common concern among new parents. The breast swelling should go away by the second week after birth as the hormones leaves from the newborn's body. Do not squeeze or massage the newborn's breasts because this can cause an infection under the skin (abscess ).

The hormones may also cause some fluid to leak from the infant's nipples. This is called witch's milk. It is common and usually goes away within 2 weeks.

Newborn girls may also have temporary changes in the vaginal area. The skin tissue around the vainal area, called the labia, may look puffy as a result of the estrogen exposure. The baby girls may also have a white fluid (discharge) from the vagina. This is called physiologic leukorrhea. There may also be slighly bleeding from the vagina. These changes are common and should slowly go away over the first 2 months of life.