Insulin in Pregnancy

Insulin in pregnancy controls maternal glucose with tight targets to lower the risk of congenital anomalies, pre-eclampsia, macrosomia, stillbirth and neonatal hypoglycaemia. It is used in pre-existing type 1 and type 2 diabetes and in gestational diabetes when lifestyle change and metformin are not enough. Requirements change across pregnancy and fall sharply after delivery.

Targets. Fasting under 5.3 mmol/L, 1 hour after meals under 7.8 mmol/L, and 2 hours after meals under 6.4 to 6.7 mmol/L. Aim for an HbA1c under 48 mmol/mol (6.5%) before and in early pregnancy if safe, without hypoglycaemia.

Pre-pregnancy. Folic acid 5 mg orally daily from before conception until 12 weeks, stop teratogenic drugs, and stop statins and angiotensin converting enzyme inhibitors.

Insulin needs. Often fall in the first trimester, rise from 16 to 36 weeks, and fall again after 36 weeks.

Basal. Isophane insulin, detemir or glargine. Degludec has growing safety data.

Mealtime. Aspart or lispro. Human soluble insulin if analogues are not available.

Gestational diabetes. Lifestyle for 1 to 2 weeks, then metformin or insulin if targets are missed. Insulin is added when fasting glucose is over 7.0 mmol/L at diagnosis, or when targets are not met on metformin.

Stop in pregnancy. SGLT2 inhibitors, GLP 1 receptor agonists, DPP 4 inhibitors, sulphonylureas (except glibenclamide in selected practice), pioglitazone, statins, and angiotensin converting enzyme inhibitors or angiotensin receptor blockers.

Aspirin. 75 to 150 mg orally at night from 12 weeks to 36 weeks to reduce pre-eclampsia risk.

Pre-existing diabetes. Total daily dose is often about 0.7 units/kg in the first trimester, 0.8 units/kg at 18 to 26 weeks, 0.9 units/kg at 26 to 36 weeks, and 1.0 unit/kg at 36 to 40 weeks, divided as 50% basal and 50% mealtime. Titrate by glucose, not by formula.

Gestational diabetes. Start isophane insulin 0.2 units/kg at bedtime for raised fasting glucose, and rapid-acting insulin 4 units before meals for raised post-meal glucose. Titrate by 2 units every 3 days.

Antenatal corticosteroids. Betamethasone raises glucose for 48 to 72 hours. Increase insulin by 20% on day 1, 40% on day 2, 40% on day 3, then return to baseline, with monitoring. Intravenous insulin may be needed.

Labour and delivery. Target 4 to 7 mmol/L. Check glucose hourly and start a variable rate infusion with glucose if glucose is over 7 mmol/L.

After delivery. - Pre-existing diabetes: reduce insulin to pre-pregnancy doses or by 50% immediately, then titrate. - Gestational diabetes: stop insulin and metformin; check fasting glucose before discharge, and an oral glucose tolerance test at 6 to 13 weeks. - Breastfeeding: reduce insulin by 10 to 20% and offer a snack before feeds.

Special groups. - Kidney impairment: close dose adjustment with nephrology input. - Liver disease: rare; specialist care. - Hyperemesis and illness: sick-day rules; check ketones. - East Africa: use mmol/L targets consistently, and plan transport and storage for insulin at home.

Monitoring. Capillary glucose fasting and after meals (1 or 2 hours), plus bedtime and 03:00 checks if hypoglycaemia occurs. HbA1c each trimester. Foetal growth scans from 28 weeks. Retinal assessment in each trimester in pre-existing diabetes. Ketones when unwell.

Hypoglycaemia. Give 15 to 20 g of fast-acting carbohydrate; glucagon 1 mg intramuscularly if unconscious.

Stopping. Stop insulin in gestational diabetes after delivery.

Referral and escalation. Refer to a joint diabetes and obstetric clinic for any pre-existing diabetes, fasting glucose over 7.0 mmol/L, recurrent hypoglycaemia, ketones, or an estimated foetal weight over the 90th centile.