Nearly all women will experience some hyperpigmentation or darkening of their skin during pregnancy which is due to the high levels of estrogen. This happens mostly in the armpits, areolae, midline of the abdomen, and genitals.
Hyperpigmentation is more common in women with a darker complexion and sun exposure will make the pigmentation darker.
Many women also get patches of dark skin on their face called melasma. It will often go away after pregnancy. If the hyperpigmentation does not go away, you can treat it after you have finished nursing with prescription hydroquinone preparations.
The best prevention is to minimize sun exposure and to use strong sun block during pregnancy (SPF 30 or greater). Remember that most clothes do not block the sun’s rays entirely.