Linea nigra (Latin for “black line”) is a dark vertical line that appears on the abdomen during 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.
Image source Amy Neeson flickr (link).
This Linea nigra is due to increased Estrogen levels, which alsocauses Melasma and darkened nipples. The purpose of this hyper-pigmentation is unknown. (source wikipedia)Other similar posts