Introduction
Diabetes complicates about 5–15% of pregnancies, mostly as gestational diabetes (GDM). Pregnancy is a diabetogenic state: hPL, cortisol and progesterone cause insulin resistance in the second half.
Screening and diagnosis of GDM
Risk factors: BMI > 30, previous GDM or macrosomic baby (≥ 4.5 kg), family history of diabetes, high-risk ethnicity, PCOS. A 75 g oral glucose tolerance test at 24–28 weeks is used (earlier if previous GDM).
Management
- Pre-pregnancy: HbA1c below about 6.5% (48 mmol/mol), folic acid 5 mg, review drugs (stop ACE inhibitors, statins), retinal and kidney checks.
- Diet and exercise first for GDM; self-monitoring of glucose (targets: fasting < 5.3 mmol/L, 1 h after meals < 7.8 or 2 h < 6.4).
- Insulin if targets are not met (metformin is an alternative or addition); insulin needs rise through pregnancy.
- Ultrasound for growth and liquor; detailed anomaly and heart scan in pre-existing diabetes.
- Timing: deliver by about 37⁺⁰–38⁺⁶ weeks for pre-existing diabetes, by 40⁺⁶ for diet-controlled GDM; caesarean section if the estimated weight is very high.
- In labour: IV insulin and glucose infusion with hourly glucose; check the baby's glucose early and feed early.
- After GDM: stop treatment after birth; fasting glucose or HbA1c at 6–13 weeks and yearly checks.
Maternal glucose crosses the placenta but insulin does not: the fetus makes its own insulin, grows large, and becomes hypoglycaemic after the cord is cut.