30th June 2023

Diabetes

The impact of diabetes on pregnancy is linked to pre-pregnancy control and pre-existing complications. The outcomes for both women with diabetes and their babies are improved by tight glycaemic control in the months leading up to conception as well as during pregnancy itself.

Hyperglycaemia results in increased fetal insulin production alongside insulin-like growth factors. Chronic hyperglycaemia leads to a macrosomic fetus as the insulin converts the excess glucose for storage; polyhydramnios (excess amniotic fluid) is also seen. Target levels for fasting blood glucose in pregnancy are 5.3 – 7.8 an hour after meals.

Recent advances have resulted in all pregnant women with pre-existing diabetes meeting the criteria for continuous glucose monitoring and more are also being offered insulin pumps.

A higher HbA1c at conception is proportionately linked to an increased risk of congenital abnormalities. The background microvascular changes also increase the risk of placental insufficiency and pre-eclampsia. Women with pre-existing diabetes in pregnancy are therefore advised to take high dose folic acid (5mg) until 12/40 and 150mg aspirin until term.

Type 1 diabetes

Insulin requirements can at least double by the end of pregnancy due to the growing fetus as well as increased insulin resistance. Increased cardiac output can lead to a rapid worsening of pre-existing end organ damage.

Baseline renal function should be checked at the beginning of pregnancy, including albumin-creatinine ratio, and retinal screening should be performed at booking and 28/40 with more frequent assessment if retinopathy is present.

ACE inhibitors and angiotensin receptor blockers (ARBs) are contraindicated in pregnancy and need to be stopped pre-conception if possible. Statins should also be stopped.

Type 2 diabetes/monogenic diabetes

There is little difference between type 1 and type 2 diabetes in terms of pregnancy outcomes. As the insulin resistance increases and due to the tighter sugar control required, many women with type 2 diabetes require the addition of exogenous insulin.

Metformin is not licensed in pregnancy but is considered safe to use. Other oral blood glucose therapies should be stopped, as should ACE inhibitors, ARBs, and statins.
Women with monogenic diabetes should be seen in joint diabetic clinic, but their management depends on whether the fetus has inherited the same genetic mutation; if the mutation is present, the fetus will not be affected by the hyperglycaemia significantly, and growth will be normal.