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. it's due to increased melanocyte-stimulating hormone made by the placenta,which also causes melasma and darkened nipples.
so called linear nigra,present in late pregnant women
Lina nigra one of the marks which happened in pregnant women it may accompanied by straie gravidarum