Most women with GDM have no recognizable symptoms. However, leaving GDM undiagnosed and untreated is dangerous to the developing fetus. Left untreated, a woman with diabetes will have consistently high blood sugar. This sugar will cross the placenta and the unborn baby's pancreas will respond to this high level of sugar by constantly producing large amounts of insulin. The insulin will allow the cells of the fetus to take in glucose, where it will be converted to fat and stored. A fetus that has been exposed to consistently high levels of sugar may be abnormally large. Such a baby may grow so large that he or she cannot be born through the vagina, but will instead need to be born through a surgical procedure (cesarean section).
Furthermore, when the baby is born, the baby will still have an abnormally large amount of insulin circulating in the blood. After birth, when the mother and baby are no longer connected via the placenta and umbilical cord, the baby will no longer be receiving the mother's high level of sugar. The baby's high level of insulin, however, will very quickly use up the glucose circulating in the its bloodstream, predisposing the baby to a dangerously low level of blood glucose (i.e., a condition called hypoglycemia).
Mark A. Mitchell, The Gale Group Inc., Gale, Detroit,