Diabetic Embryopathy

Why high blood sugar causes birth defects

The baby's major organs form between about 3 and 8 weeks after conception, often before a person knows they are pregnant. High glucose levels during this window disturb normal cell signaling and increase oxidative stress in the embryo, which leads to cell death in developing tissues and abnormal folding of structures such as the heart and neural tube.

Risk rises steadily with higher blood sugar. Studies show that an HbA1c near normal around conception gives a risk close to the general population (about 2 to 3%). The risk increases several-fold as HbA1c rises, with the highest rates at HbA1c levels above 10%.

Gestational diabetes, which develops in the second half of pregnancy, does not cause these early structural defects, though undiagnosed type 2 diabetes picked up in pregnancy can.

Defects linked to maternal diabetes

Caudal regression syndrome is rare, but much more common in babies of mothers with diabetes than in the general population, making it the defect most strongly linked to diabetes.

Heart defects are the most common. See congenital heart defects and neural tube defects.

Other effects of diabetes in pregnancy

Diabetic embryopathy refers to early structural defects. Diabetes also affects the baby later in pregnancy (sometimes called diabetic fetopathy):

• macrosomia (a large baby) and birth injury
• low blood sugar in the newborn
• breathing problems
• jaundice
• stillbirth risk, especially with poor control

It also raises the risk of miscarriage, preeclampsia and preterm birth.

Diagnosis and screening in pregnancy

People with pre-existing diabetes are offered:

• an early dating ultrasound
• first-trimester screening, which can sometimes detect major defects
• a detailed anatomy scan at about 18 to 22 weeks
• fetal echocardiography, an ultrasound of the baby's heart, often at around 20 to 24 weeks
• HbA1c measurements at booking to help estimate risk

If a defect is found, the team arranges counseling with specialists in fetal medicine, pediatric cardiology or surgery, and plans delivery at a hospital that can care for the baby.

Prevention

Diabetic embryopathy is largely preventable with planning.

Before pregnancy

• Aim for an HbA1c below 6.5% (48 mmol/mol) before conception if it can be achieved safely without frequent low blood sugars, as recommended by the American Diabetes Association.
• Use reliable contraception until blood sugar is well controlled.
• Take higher-dose folic acid before conception and during early pregnancy. Many guidelines recommend a higher dose than standard for people with diabetes. Ask your clinician for the right dose.
• Review medicines: ACE inhibitors, ARBs and statins are usually stopped before or as soon as pregnancy is confirmed. Some diabetes tablets may be switched to insulin.
• Check for complications: eye, kidney and thyroid checks.
• Consider continuous glucose monitoring and insulin pumps, which help tighten control.

During early pregnancy

• frequent glucose monitoring, with targets set by your care team
• early referral to a specialist diabetes and pregnancy clinic
• glucagon at home and a plan for managing low blood sugars, which become more common in early pregnancy

Outlook

Outcomes depend on the type and severity of the defect. Many heart defects can be repaired surgically. Neural tube defects and caudal regression syndrome may cause lasting disability and need multidisciplinary care. Most babies of mothers with well-controlled diabetes are born healthy.

Frequently asked questions

What is diabetic embryopathy?

Diabetic embryopathy is the pattern of birth defects that can occur when a pregnant person has high blood sugar during the first 8 weeks of pregnancy, when organs form. It is linked to type 1 and type 2 diabetes that existed before pregnancy.

What birth defects are caused by diabetes in pregnancy?

The most common are heart defects. Others include neural tube defects such as spina bifida, kidney and urinary tract malformations, cleft lip and palate, and caudal regression syndrome, a rare underdevelopment of the lower spine and legs that is strongly linked to maternal diabetes.

Does gestational diabetes cause birth defects?

Gestational diabetes usually develops after organs have formed, so it does not cause the early structural defects of diabetic embryopathy. It can cause a large baby and newborn low blood sugar. Type 2 diabetes first discovered in early pregnancy does carry a higher risk.

What HbA1c is safe for pregnancy?

The American Diabetes Association recommends an HbA1c below 6.5% before conception if this can be reached without significant low blood sugars. Risk of birth defects rises as HbA1c increases. Your diabetes team will set individual targets.

Can diabetic embryopathy be prevented?

Largely, yes. Planning pregnancy, achieving good blood sugar control before conception, taking higher-dose folic acid, and reviewing medicines with your doctor significantly reduce the risk. Early specialist care in pregnancy also improves outcomes.