Pregnancy causes physiological changes in the body which includes tanning of skin variably. Post pregnancy within 6-8 weeks, most of the pregnancy induced changes revert back to pre-
pregnant state.
Fee highly pigmented skin changes like the stretch marks over abdomen, thighs and buttocks may need therapeutic management like applying skin lightening cream and lotions for fee months. They help a lot in many cases.
Please be advised that do not go for aggressive therapies and instant results. All skin color are beautiful when you are healthy and fit.
Thanks.