What is the risk of stillbirth in a pregnancy with well‑controlled gestational diabetes?

Risk of Stillbirth in Well-Controlled Gestational Diabetes

The risk of stillbirth in well-controlled gestational diabetes is extremely low, approaching that of the general population, with landmark trial data showing zero stillbirths among 490 treated GDM patients compared to 5 stillbirths/neonatal deaths among 510 untreated patients. 1

Evidence from Randomized Controlled Trials

The ACHOIS trial provides the highest quality evidence on this question. When women with mild gestational diabetes received dietary management, glucose monitoring, and insulin treatment as needed after 24 weeks' gestation:

• Zero perinatal deaths occurred among 490 babies born to treated mothers 1
• In contrast, 5 total stillbirths or neonatal deaths occurred among 510 untreated women 1
• This represents a complete elimination of perinatal mortality with treatment, though the absolute numbers were small 1

Understanding the Risk Gradient

The stillbirth risk in diabetes exists on a spectrum based on glycemic control and diabetes type:

• Severe fasting hyperglycemia (>105 mg/dL) during the last 4-8 weeks of gestation specifically increases intrauterine fetal death risk 2
• Pre-gestational diabetes carries significantly greater stillbirth risk than GDM, with 3- to 5-fold increased odds compared to non-diabetic pregnancies 3
• Well-controlled GDM (meeting targets of fasting <95 mg/dL, 1-hour postprandial <140 mg/dL) has minimal excess stillbirth risk 1, 2

Pathophysiology When Control Is Suboptimal

When glycemic control deteriorates, stillbirth risk increases through:

• Fetal hypoxia and cardiac dysfunction secondary to maternal hyperglycemia 4
• Fetal anaerobic metabolism with hypoxia and acidosis 5
• More than 50% of diabetic stillbirths remain unexplained even when these mechanisms are considered 4

Clinical Implications for Surveillance

For women with well-controlled GDM on diet/exercise alone with appropriate fetal growth, data are insufficient to determine whether surveillance beyond self-monitoring of fetal movements is indicated 1

However, intensified fetal surveillance is reasonable when:

• Pregnancy continues beyond 40 weeks' gestation 1
• Insulin or glyburide therapy is required 1
• Fasting glucose remains elevated despite treatment 2

Critical Distinction from Pre-Gestational Diabetes

The evidence clearly separates GDM from pre-existing diabetes:

• Pre-gestational diabetes confers "significantly greater risk than GDM" 1
• Type 2 diabetes shows higher third-trimester stillbirth prevalence compared to Type 1 diabetes 2
• GDM represents approximately 7% of pregnancies with much lower baseline risk than pre-gestational disease 1

Common Pitfall to Avoid

Do not conflate the stillbirth risk of untreated or poorly controlled GDM with well-controlled disease. The ACHOIS trial demonstrates that treatment achieving glycemic targets essentially eliminates the excess perinatal mortality risk 1. The key is maintaining fasting glucose <95 mg/dL and postprandial glucose <140 mg/dL through diet, exercise, and insulin when needed 1, 2.