Linea nigra

Linea nigra (Latin for "black line") is a dark vertical line that appears on the abdomen in about three quarters of all pregnancies. The brownish streak is usually about a centimeter in width. The line runs vertically along the midline of the abdomen from the pubis to the umbilicus, but can also run from the pubis to the top of the abdomen. Linea nigra is due to increased melanocyte-stimulating hormone made by the placenta, which also causes melasma and darkened nipples.

Fair-skinned women show this phenomenon less often than women with darker pigmentation. Linea nigra typically disappears within a few months after delivery.