Pregestational Diabetes in Pregnancy

Pregestational diabetes is type 1 or type 2 diabetes present before conception. It differs from gestational diabetes because hyperglycemia may be present during organogenesis, when the fetal heart, neural tube, and other major structures are forming. Higher glucose exposure around conception and early pregnancy increases the risk of spontaneous abortion, congenital anomalies—particularly cardiac and neural tube defects—and stillbirth. Maternal glucose crosses the placenta; maternal insulin does not. When maternal glucose is persistently elevated later in pregnancy, the fetal pancreas responds by producing more insulin. Fetal hyperinsulinemia promotes excessive growth and fat deposition, increasing the likelihood of macrosomia, birth trauma, and neonatal hypoglycemia after birth. Once the umbilical cord is cut, maternal glucose delivery stops abruptly while the newborn’s insulin level remains high. Pregnancy also changes the mother’s insulin needs. During early pregnancy, nausea, lower food intake, and increased insulin sensitivity may reduce insulin requirements. By about 16 weeks, placental hormones progressively create insulin resistance. Insulin needs often rise about 5% each week until approximately 36 weeks and may double from the preconception dose. A sudden, unexplained fall in insulin requirement...