Increased breast size is not a listed side effect for prenatal vitamins according to WebMD. Certain exercises can help improve the appearance of the chest by targeting the chest muscles.
Some of the known side effects of prenatal vitamins are constipation, nausea and vomiting. These side effects normally decrease in intensity once the body has acclimated to the vitamin. Rarely, an allergic reaction may occur. Symptoms of an allergic reaction are itching, rash, trouble breathing and dizziness.
Women looking to increase breast size will not find success with prenatal vitamin usage. Exercises that target the chest muscles can help the chest appear firmer, rounder and perkier. Chest flies, bench presses, decline bench presses and incline bench presses are a few effective moves to help increase the size of the chest muscles.