Transformation is a novel written by Edmund Plante. It was first published in 1987.
Description[]
Something vile and violent has touched Sally Martin, and the "child" within her is not her husband's--or any other man's. Then her body becomes pale and bloated, her shining hair falls out, and her jaundiced eyes can no longer stand sunlight. The transformation is complete. The thing inside Sally is waiting to break free and spread its evil.