Have you developed some dark patches on your cheeks? Don't worry. Pigmentation is a very common symptom in pregnancy, though noone knows what causes it.
But the patches usually fade away after childbirth. The skin on the abdomen and breasts stretches as the uterus grows in size.
So does the skin on the arms and thighs if you have put on a lot of weight. This leaves stretch marks on your skin after the delivery. But, if you haven't put on too much weight, the discolouration of the skin is not particularly noticeable after the tissues go back to their original shape.