Why Pregnancy Causes Insulin Resistance

The odd thing about gestational diabetes is that the process behind it is entirely normal. It is a normal process taken further than your pancreas can match.

Your baby needs a steady supply of glucose. To provide it, the placenta produces hormones that reduce how well your own cells respond to insulin. Glucose that would otherwise be taken up by your muscles stays available in your blood, where it can cross to the baby.

So insulin resistance in pregnancy is deliberate. Every pregnant person develops some.

Your pancreas compensates by making considerably more insulin than usual. In most pregnancies it keeps pace and blood sugar stays normal. In GDM it cannot quite keep up, and glucose starts running high.

This explains two things that otherwise seem strange.

It explains the timing. Placental hormone production rises as the pregnancy progresses, which is why screening is done between 24 and 28 weeks — that is when the strain is becoming apparent, but with time still left to act.

And it explains why insulin needs typically climb through the third trimester and then fall sharply once the placenta is delivered. The hormones causing the resistance leave with it.