Insulin for Gestational Diabetes: Is It Safe?

What does the evidence say about insulin for gestational diabetes during pregnancy?

1. When blood glucose isn't well controlled during pregnancy, there is a higher chance of miscarriage, stillbirth, preeclampsia, excess amniotic fluid, and preterm delivery, plus newborn complications like low blood sugar, jaundice, breathing difficulty, and macrosomia, with some babies weighing over 10 pounds. Most gestational diabetes is managed first with diet changes and exercise, with medication added when needed. 1
2. Insulin itself does not cross the placenta because of its size, but glucose crosses freely. When maternal blood sugar runs high, that excess glucose reaches the fetus directly and triggers the fetal pancreas to release its own extra insulin, which is the actual mechanism behind an oversized baby, not the insulin a mother injects. 2
3. In safety data reviewed by MotherToBaby, insulin aspart (Novolog) was not linked to a higher chance of birth defects, miscarriage, preterm delivery, or low birth weight beyond the background rate, which is about 3 in 100 pregnancies for birth defects regardless. 3
4. Among more than 800 reported pregnancies with insulin glargine (Lantus) use throughout pregnancy, there was no reported increase in birth defects or miscarriage. 4
5. Insulin aspart is expected to pass into breast milk, but this has not been linked to increased risk for nursing infants. 3

Is insulin for gestational diabetes safe in each trimester?

• First trimester. Type 1 or type 2 diabetes identified before pregnancy often already involves insulin, and good control matters most right from the start, since unmanaged high blood sugar in early pregnancy raises the chance of miscarriage.
• Second trimester. Gestational diabetes is usually screened for around 24 to 28 weeks with a glucose tolerance test, and most people manage it with diet and exercise first. Insulin gets added when those steps aren't enough to keep glucose in range.
• Third trimester. Insulin needs typically climb as pregnancy progresses, since pregnancy hormones increase insulin resistance later on. Expect dose adjustments through the third trimester, and your care team will watch for a larger-than-average baby, a sign that blood sugar control needs a closer look.