Gestational diabetes
Placental hormones progressively induce maternal insulin resistance through pregnancy, and gestational diabetes emerges when the pancreas cannot secrete enough extra insulin to compensate, leaving glucose (and its downstream fetal effects) uncontrolled.
First principles
The placenta deliberately makes the mother insulin-resistant
As the placenta grows it secretes human placental lactogen, progesterone and cortisol in rising amounts, all of which antagonise insulin action at the cellular level. This is a normal, purposeful adaptation: by making maternal tissues less responsive to insulin, more glucose is diverted across the placenta to fuel fetal growth. In most women the maternal pancreas simply increases insulin output to match, and glucose stays controlled.
Educational content pending clinical review. Not medical advice.