This dark line may appear between the belly button and the pubic bone. It is a hormone-induced excess production of brown material (pigment) in the skin cells in this area. After delivery, the line begins to fade.
Some women produce a brownish pigmentation of the skin over the face and forehead, known as the 'mask of pregnancy'. It begins about the 16th week of pregnancy and fades after delivery.
As the woman's weight increases, the skin stretches over the abdomen, thighs, and breasts. Pink or brownish stretch marks may appear in some women and usually fade after delivery.
Activity of the sweat glands throughout the body usually increases during pregnancy, which causes the woman to sweat more profusely than usual.