Changes in size of melanocytic nevi during pregnancy

The relation between pregnancy, melanocytic nevi, and malignant melanoma is ambiguous. It has been reported that nevi grow and darken during pregnancy. Several recent studies have shown that malignant melanomas diagnosed during pregnancy are thicker than those not associated with pregnancy. This may be partially due to a delay in diagnosis because of the opinion that benign nevi change during pregnancy.

Our purpose was to photographically document any change in size of melanocytic nevi during pregnancy.

Twenty-two women were entered into the study during the first trimester of pregnancy and examined again in the third trimester. All nevi 2 mm or larger on their back were documented and photographed. Photographs were then compared and nevi measured for change in diameter.

Of 129 nevi, only eight nevi (6.2%) changed in diameter from the first to the third trimester. The mean change in size of all nevi studied was zero. Of the eight nevi that did change in size, four increased by 1 mm and four decreased by 1 mm.

Our study suggests that pregnancy is not associated with any significant change in size of melanocytic nevi. Patient characteristics (age, pregnancy number, skin type) and nevi characteristics (location, number) did not correlate with any change in size.