Pre-existing Type 1 Diabetes in Pregnancy

Preexisting type 1 diabetes in pregnancy is autoimmune insulin deficiency present before conception that needs lifelong insulin. High glucose around conception raises the risk of miscarriage, congenital anomaly, stillbirth, macrosomia, preeclampsia and neonatal hypoglycaemia, and pregnancy can worsen retinopathy and nephropathy.

• Anomaly risk is higher and rises with HbA1c above 6.5 percent at conception.
• Insulin needs fall at 8 to 14 weeks, rise steadily through the second and third trimesters, and fall sharply after delivery of the placenta.
• Hypoglycaemia unawareness and ketoacidosis are the main maternal dangers.

A woman with known type 1 diabetes presents with a confirmed pregnancy, often with nausea, vomiting and erratic glucose readings, and may already have retinopathy, nephropathy, neuropathy or hypertension. Examine blood pressure, fundi, feet, injection sites and fundal height.

• Frequent hypoglycaemia in the first trimester, especially with vomiting.
• Ketoacidosis can develop at glucose below 11 mmol/L.
• Fundal height large for dates suggests macrosomia or polyhydramnios.
• Differential diagnosis: type 2 diabetes, monogenic diabetes, gestational diabetes needing insulin, hyperemesis with ketosis, infection.
• Complications: diabetic ketoacidosis, severe hypoglycaemia, congenital anomaly, preeclampsia, polyhydramnios, macrosomia, shoulder dystocia, stillbirth, preterm birth, progression of retinopathy and nephropathy, neonatal hypoglycaemia.

The diagnosis is already established; the approach is to measure control and screen for complications and fetal anomaly.

• Capillary glucose targets: fasting 3.5 to 5.3 mmol/L, 1 hour after meals below 7.8 mmol/L, 2 hours after meals below 6.4 mmol/L; test at least 7 times daily.
• HbA1c at booking and every 4 to 8 weeks; target below 6.5 percent, below 6.0 percent if safe.
• Urine albumin to creatinine ratio (above 3 mg/mmol abnormal), serum creatinine, blood pressure, retinal examination at booking, 16 to 20 weeks and 28 weeks.
• Ultrasound for dating, anomaly scan at 18 to 20 weeks, fetal heart scan at 20 to 22 weeks, growth scans every 4 weeks from 28 weeks.
• Urine ketones or blood ketones above 1.5 mmol/L when unwell.

The principle is near normal glucose without hypoglycaemia, started before conception, with screening for complications and planned delivery.

• Supportive: carbohydrate counting with 3 meals and 3 snacks; walking 30 minutes daily; stop smoking and alcohol; teach hypoglycaemia and sick day rules; keep glucose tablets and glucagon at home; weight gain of 11.5 to 16 kg for normal weight.
• Pharmacological: folic acid 5 mg oral daily from preconception to 12 weeks; aspirin 150 mg oral at night from 12 weeks to 36 weeks; isophane insulin 0.2 units/kg subcutaneous at bedtime (split morning and night as pregnancy advances) plus soluble insulin 0.1 units/kg subcutaneous 30 minutes before each main meal, adjusted by 2 units every 2 to 3 days; total daily dose about 0.7 units/kg in the first trimester, 0.8 in the second and 0.9 to 1.0 in the third; insulin glargine and insulin aspart or lispro may replace these where available; stop ACE inhibitors, angiotensin receptor blockers and statins and use methyldopa 250 to 500 mg oral 8-hourly (maximum 3 g daily) or nifedipine modified release 30 to 60 mg oral daily for blood pressure above 140/90 mmHg; betamethasone 12 mg IM twice, 24 hours apart, if delivery is needed before 34 weeks, with insulin increased by 25 to 40 percent for 72 hours.
• Procedures: induction of labour or caesarean section at 37 weeks to 38 weeks and 6 days; caesarean section if estimated fetal weight is above 4500 g; in labour check glucose hourly (target 4 to 7 mmol/L) and start soluble insulin infusion 1 to 2 units/hour with dextrose 5 percent 100 mL/hour if above 7 mmol/L.
• Special groups: nephropathy with creatinine above 120 micromol/L needs fortnightly review and early delivery; proliferative retinopathy needs laser photocoagulation before delivery; after delivery return insulin to the pre-pregnancy dose or reduce by 50 percent in the first 24 hours; breastfeeding lowers glucose, so reduce insulin as glucose readings guide and eat a snack before feeds; neonates feed within 30 minutes of birth, check glucose at 2 to 4 hours, and treat glucose below 2.6 mmol/L with dextrose 10 percent 2 mL/kg IV over 10 minutes.
• Red flags: glucose below 3.5 mmol/L with confusion, ketones above 1.5 mmol/L, vomiting, reduced fetal movements, blood pressure above 140/90 mmHg, visual change.
• Follow-up: review every 1 to 2 weeks; HbA1c every 4 to 6 weeks; contraception before discharge; review at 6 weeks; annual eye and kidney checks.