Twin Pregnancy with Gestational Diabetes

Twin pregnancy with gestational diabetes is glucose intolerance first found in pregnancy in a woman carrying twins. It arises from the larger placental mass and greater insulin resistance. It matters because it adds risk of preeclampsia, caesarean section, macrosomia in one twin and neonatal hypoglycaemia to the risks of twin pregnancy.

• Risk factors: obesity, previous gestational diabetes, family history, age above 35 years, assisted conception.
• Screening is by a 75 g oral glucose tolerance test at 24 to 28 weeks, and earlier in high risk women.
• Insulin needs are higher than in singleton pregnancy.

Most women have no symptoms. Others have thirst, polyuria, recurrent candidiasis or a uterus larger than expected for twins.

• Large for dates uterus, with polyhydramnios in some.
• Excess weight gain.
• Differential diagnosis: preexisting type 2 diabetes, type 1 diabetes, steroid induced hyperglycaemia, renal glycosuria, polyhydramnios from twin transfusion syndrome.
• Complications: preeclampsia, macrosomia, discordant growth, polyhydramnios, preterm birth, caesarean section, neonatal hypoglycaemia, stillbirth, later type 2 diabetes.

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

• 75 g oral glucose tolerance test after an overnight fast: fasting 5.1 mmol/L or more, 1 hour 10.0 mmol/L or more, or 2 hours 8.5 mmol/L or more; test at booking and at 24 to 28 weeks in women with risk factors.
• Fasting glucose 7.0 mmol/L or more, random glucose 11.1 mmol/L or more or HbA1c 6.5 percent or more suggests overt diabetes.
• Capillary glucose: fasting and 1 hour after each meal, with targets fasting below 5.3, 1 hour below 7.8 and 2 hours below 6.4 mmol/L.
• Growth scans of both twins every 2 to 4 weeks from 24 weeks.

The principle is diet and exercise, then metformin or insulin when targets are missed, with delivery at 37 weeks.

• Supportive: dietitian review with 40 to 45 percent carbohydrate and a high energy plan appropriate for twins; walking 30 minutes after meals; teach glucose testing and insulin injection; birth in a unit with neonatal intensive care.
• Pharmacological: metformin 500 mg oral with meals increased to 1 g 12-hourly (maximum 2.5 g daily); isophane insulin 0.2 units/kg subcutaneous at bedtime plus soluble insulin 4 to 6 units subcutaneous before meals, adjusted by 2 units every 3 days; aspirin 150 mg oral at night from 12 weeks to 36 weeks; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days if delivery is likely, with insulin increased by 25 to 40 percent for 72 hours; oxytocin 10 IU IM at birth.
• Procedures: delivery at 37 weeks for diet or drug controlled disease, and at 36 weeks for monochorionic twins or poor control; vaginal birth if the first twin is cephalic, with hourly glucose in labour (target 4 to 7 mmol/L) and soluble insulin infusion 1 to 2 units per hour for glucose above 7 mmol/L; caesarean section for first twin non cephalic or obstetric reasons.
• Special groups: after birth stop insulin and metformin; newborns feed within 30 minutes and have glucose checked at 2 hours, with glucose below 2.6 mmol/L treated by dextrose 10 percent 2 mL/kg IV over 10 minutes then 80 mL/kg per day.
• Red flags: glucose above 15 mmol/L, ketones, reduced fetal movements, rapidly increasing abdominal size, blood pressure 140/90 mmHg or more.
• Follow-up: antenatal review every 2 weeks; growth scans every 2 to 4 weeks; 75 g oral glucose tolerance test or fasting glucose at 6 to 13 weeks postpartum; HbA1c yearly.