Diet-Controlled Gestational Diabetes

Diet controlled gestational diabetes is glucose intolerance first found in pregnancy that stays within targets using diet and activity alone. It results from placental hormone induced insulin resistance. It matters because glucose can rise later in pregnancy and needs regular monitoring, and the mother has a high risk of type 2 diabetes later.

• Risk factors: body mass index above 30 kg/m2, previous gestational diabetes, family history, age above 35 years.
• Diagnosis by 75 g oral glucose tolerance test at 24 to 28 weeks.
• Risk of macrosomia is lower than with drug treated disease.

Most women have no symptoms. A few have thirst, polyuria or recurrent candidiasis. Fundal height may be normal or large for dates.

• Often found on screening.
• Weight gain may be excessive.
• Differential diagnosis: preexisting type 2 diabetes, renal glycosuria, steroid effect, type 1 diabetes.
• Complications: macrosomia, polyhydramnios, preeclampsia, shoulder dystocia, caesarean section, neonatal hypoglycaemia, later type 2 diabetes.

The approach is the 75 g oral glucose tolerance test and glucose monitoring.

• 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, 2 hours 8.5 mmol/L or above.
• Capillary glucose tests: fasting and 1 hour after each meal; targets fasting below 5.3, 1 hour below 7.8, 2 hours below 6.4 mmol/L.
• Growth scan at 28 and 36 weeks; urine for ketones if unwell.
• HbA1c baseline.

The principle is diet and exercise with drug treatment started if targets are missed for 1 to 2 weeks.

• Supportive: 3 meals and 2 to 3 snacks with 40 to 45 percent carbohydrate, including whole grain maize meal, beans, vegetables and minimal sugar; avoid sodas and juice; walking 30 minutes after meals; weight gain of 7 to 11.5 kg for overweight women; test glucose 4 times daily.
• Pharmacological: none while glucose is on target; if fasting is above 5.3 or 1 hour is above 7.8 mmol/L on two readings in a week start metformin 500 mg oral once daily with a meal increased to 1 g 12-hourly (maximum 2.5 g daily), or isophane insulin 0.2 units/kg subcutaneous at bedtime for fasting values and soluble insulin 4 to 6 units subcutaneous before meals for high post meal values.
• Procedures: wait for spontaneous labour or induce by 40 weeks and 6 days; caesarean section only for obstetric indications or estimated fetal weight above 4500 g.
• Special groups: after delivery no treatment is needed; neonates feed early and have glucose checked at 2 to 4 hours, treating glucose below 2.6 mmol/L with dextrose 10 percent 2 mL/kg IV over 10 minutes.
• Red flags: glucose above 7.8 mmol/L at 1 hour on repeated days, ketones, reduced fetal movements, polyhydramnios.
• Follow-up: review every 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 breastfeeding.