It is a widely held belief that moles or nevi change during pregnancy. However, there is no convincing evidence to support this. There are many changes that happen to a woman’s skin when she is pregnant. She may develop melasma, brown splotches on her face, or linea nigra, brown pigmentation on her belly. She may also develop benign growths such as skin tags or angiomas.
It might be that some of these skin changes are misinterpreted as changes in the size or color of already existing moles. Also, since women’s skin stretches during pregnancy, moles might appear to be growing or spreading. This is not the same as a mole actually changing. According to an new review published in the December 2007 issue of the Journal of the American Academy of Dermatology:
The best data available … suggest that nevi do not typically change over the course of pregnancy; therefore a changing nevus during pregnancy should undergo biopsy, just as in a nonpregnant patient.
If you are pregnant, or are a physician who has a pregnant patient with a changing mole or nevus, then it should be evaluated by a dermatologist. Though uncommon, a new or changing nevus, can be a melanoma skin cancer.