What if gestational diabetes mellitus (GDM) is not created by pregnancy, but is a pre-existing metabolic vulnerability revealed by it?

Pregnancy is a metabolic stress test. As gestation progresses, placental hormones increase insulin resistance, maternal weight usually increases, fetal growth accelerates and fetoplacental demands rise. For most women, the pancreas compensates.

But what happens when metabolic reserve is already reduced?

Pre-existing adiposity, weight gain and other factors may leave some women with limited reserve. Pregnancy may then push an already compensating system beyond its capacity, making hyperglycaemia visible. This may explain why GDM is usually recognised during the latter half of pregnancy.

Multiple pregnancy offers an intriguing clue. Two or more fetuses and greater placental mass impos ...