GDM, or Diabetes You Already Had?
Reviewed by CDE Mehandi Sharma · Updated
Not all diabetes discovered during pregnancy is gestational diabetes. The distinction matters, and it is often glossed over.
True GDM develops during the pregnancy because of placental hormones, and typically resolves after delivery. Pre-existing diabetes — Type 2 most often, sometimes Type 1 — was already there and simply had not been diagnosed until a pregnancy test found it.
The clue is usually timing and severity. Diabetes found at the first antenatal visit, or very early in the pregnancy, is more likely to be pre-existing, because placental hormone effects have not built up yet. Very high readings at diagnosis point the same way.
India's national study found GDM in 19.2% of pregnancies before 20 weeks and 23.4% at or after 20 weeks, so early diagnoses are not rare and deserve a second look rather than an assumption.
Why it matters. Pre-existing diabetes needs different management during the pregnancy, and it does not go away afterwards — so your care continues rather than concluding at delivery.
This is one of the strongest arguments for actually doing the postpartum glucose test. It is what separates GDM that resolved from diabetes that was there all along and still is.