Linea nigra

This is the vertical line that appears down the middle of your belly around the fourth or fifth month of pregnancy. 

What is it?
This line may have always been there, but you may never have noticed it before because of its light color. Prior to pregnancy, the line is light or pale and is called the linea alba (white line). It runs from your navel to the pubic bone and just darkens during pregnancy, giving it the name linea nigra (black line). However, the line is never really black during pregnancy. It is brownish and darker in color.  It is normally about ¼ to ½ inch wide and stretches vertically down your belly from the umbilicus to the pubis. The pregnancy line or linea nigra usually grows darker as your pregnancy develops. 

Why do I have it?
Although the specific cause of the linea nigra is unknown, it is believed to be related to hormonal changes which cause changes in skin pigmentation. One theory is that the melanocyte-stimulating hormone produced by the placenta is the main contributing factor. This hormone is also believed to cause the darkening around the nipples. Not every pregnant woman gets a linea nigra, so don’t worry if you don’t have one during your pregnancy.

What can I do?
There is nothing you can do to prevent this from occurring. The line will naturally fade after your pregnancy.