The dark line on your pregnant stomach is known as the linea nigra.
In some cases, it is called the pregnancy line. Around 80% of pregnant ladies will see the linea nigra structure during pregnancy.
It ordinarily appears after the main trimester. It isn’t interesting to pregnancy. It can form when you are not pregnant, even in men.
The linea nigra is a latin term which literally translates to ‘black line’. It is the name used to describe the dark vertical line which often appears on the abdomen of pregnant women around the middle of pregnancy.
You may also notice other areas of your body getting darker, like your nipples. If you have any scars, they might become more noticeable. Freckles and birthmarks may become more obvious, too.
These color changes happen because of the hormones estrogen and progesterone, which your body produces in larger amounts to help your baby develop.
Estrogen and progesterone stimulate cells called melanocytes in your skin, causing them to produce more melanin, the pigment that tans and darkens your skin. Increased melanin production is what makes your skin change color during pregnancy.
At some point during your second trimester, you may notice the dark brown line running down the middle of your abdomen, between your belly button and pubic area. This line is called the linea alba. You’ve always had it, but before your pregnancy it was too light to see.
When melanin production increases during pregnancy, the line gets darker and more obvious. Then it’s called the linea nigra.
There is nothing you can do to prevent the pregnancy line. It is a natural part of pregnancy. The good news is that it usually lessens and fades away shortly after the birth of your baby. You may think the dark line running up your stomach is unsightly. The good news is, a linea nigra is not harmful.
Source: Health Line