Ah anak, yan ay normal na darkening ng skin during pregnancy, nangyari din sa akin at sa maraming preggy friends ko, lalo na sa areas na may friction like underarms at between the thighs! It's usually from hormonal changes at the extra melanin production, tapos ang sweating and rubbing lang nag-darken pa more. Hindi ito permanent, promise, mamula-mula lang after you give birth, though it takes a few months to fade completely. Better check with your OB-GYN lang to rule out anything else, pero majority of cases talaga ito ay hormonal lang, no worries!