Insulin-Treated Gestational Diabetes

Insulin treated gestational diabetes is glucose intolerance first found in pregnancy that fails to reach targets with diet and needs insulin. It results from placental hormones causing insulin resistance. It matters because it raises the risk of macrosomia, preeclampsia, caesarean section and later type 2 diabetes.

• Risk factors: body mass index above 30 kg/m2, previous gestational diabetes, family history, previous macrosomic baby, age above 35 years.
• Diagnosis by 75 g oral glucose tolerance test at 24 to 28 weeks.
• Insulin is usually stopped after delivery.

Most women have no symptoms. Some have thirst, polyuria, recurrent candidiasis, large for dates uterus or polyhydramnios.

• Often found on screening.
• Weight gain above target.
• Differential diagnosis: preexisting type 2 diabetes, type 1 diabetes, steroid induced hyperglycaemia, renal glycosuria.
• Complications: macrosomia, shoulder dystocia, polyhydramnios, preeclampsia, caesarean section, neonatal hypoglycaemia, stillbirth, later type 2 diabetes.

The approach is 75 g oral glucose tolerance test, with treatment started when targets are missed.

• 75 g oral glucose tolerance test after an overnight fast: fasting 5.1 mmol/L or above, 1 hour 10.0 mmol/L or above, or 2 hours 8.5 mmol/L or above.
• Fasting glucose 7.0 mmol/L or above, or random 11.1 mmol/L or above, is diabetes first found in pregnancy and is treated as overt diabetes.
• Capillary glucose: fasting, 1 hour after each meal; insulin is started when fasting is above 5.3 or 1 hour above 7.8 mmol/L after 1 to 2 weeks of diet.
• Growth scan at 28 and 36 weeks; HbA1c baseline.

The principle is diet, exercise and insulin to reach glucose targets.

• Supportive: dietitian review; 3 meals and 3 snacks with 40 to 45 percent carbohydrate and low glycaemic foods; walking 30 minutes after meals; stop sugary drinks; teach finger prick testing and insulin injection; weight gain of 7 to 11.5 kg for overweight women.
• Pharmacological: isophane insulin 0.2 units/kg subcutaneous at bedtime for high fasting glucose; soluble insulin 4 to 6 units subcutaneous 30 minutes before the meal with high values; adjust by 2 units every 3 days; metformin 500 mg oral once daily with a meal increased to 1 g 12-hourly (maximum 2.5 g daily) if insulin is refused; glibenclamide 2.5 mg oral daily increased by 2.5 mg weekly to 10 mg 12-hourly (maximum 20 mg daily) if both are refused; betamethasone 12 mg IM twice, 24 hours apart, only before 34 weeks if delivery is needed.
• Procedures: induction of labour by 40 weeks and 6 days (by 38 weeks and 6 days if control is poor or macrosomia is present); caesarean section if estimated fetal weight is above 4500 g; in labour check glucose hourly (target 4 to 7 mmol/L) and give soluble insulin infusion 1 to 2 units/hour if above 7 mmol/L.
• Special groups: after delivery stop insulin; neonates feed within 30 minutes, check glucose at 2 to 4 hours, treat glucose below 2.6 mmol/L with dextrose 10 percent 2 mL/kg IV over 10 minutes; breastfeeding lowers later diabetes risk.
• Red flags: fasting glucose above 7.0 mmol/L, ketones, glucose below 3.5 mmol/L, reduced fetal movements.
• Follow-up: review every 1 to 2 weeks; 75 g oral glucose tolerance test or fasting glucose at 6 to 13 weeks postpartum; yearly HbA1c or fasting glucose; advise weight loss and exercise.