Which statement about insulin transfer across the placenta in pregnancy is true?

Which statement about insulin transfer across the placenta in pregnancy is true?

• A. Insulin readily crosses placenta and causes larger babies
• B. Insulin does not readily cross placenta and has no direct fetal metabolic effect
• C. Insulin crosses placenta and prevents fetal hypoglycemia
• D. Insulin crosses placenta and causes fetal macrosomia

Answer: (B)

Insulin is a large peptide hormone that does not cross the placenta in any meaningful amount, so maternal insulin has no direct metabolic effect on the fetus. The fetus receives glucose from the mother, and in response its own pancreas increases insulin production, which acts to promote fetal growth. This fetal insulin is what contributes to increased size (macrosomia) in babies of diabetic mothers, not maternal insulin crossing into the fetus. After birth, the baby can develop hypoglycemia due to persistent high fetal insulin levels, but that hypoglycemia is a result of the baby’s own insulin, not maternal insulin crossing the placenta. So the true statement is that insulin does not readily cross the placenta and has no direct fetal metabolic effect. The other options misstate placental transfer or the source of fetal growth effects.

Insulin is a large peptide hormone that does not cross the placenta in any meaningful amount, so maternal insulin has no direct metabolic effect on the fetus. The fetus receives glucose from the mother, and in response its own pancreas increases insulin production, which acts to promote fetal growth. This fetal insulin is what contributes to increased size (macrosomia) in babies of diabetic mothers, not maternal insulin crossing into the fetus. After birth, the baby can develop hypoglycemia due to persistent high fetal insulin levels, but that hypoglycemia is a result of the baby’s own insulin, not maternal insulin crossing the placenta.

So the true statement is that insulin does not readily cross the placenta and has no direct fetal metabolic effect. The other options misstate placental transfer or the source of fetal growth effects.