HOW DOES DIABETES AFFECT THE FETUS?

Three pathological processes have been implicated as causes of fetal compromise in diabetic pregnancies

• Fetal hypoxia
• Fetal acidemia
• Alterations in maternal fetal metabolism

 It is well known that maternal hyperglycemia causes fetal hyperglycemia. Fetal hyperglycemia causes reactive hyperinsulinemia and the resulting increase in IGF is the main cause of accelerated fetal growth. The reactive hyperinsulinemia also causes increased fetal oxygen consumption and decreased arterial oxygen levels contributing to hypoxia.

 What are the fetal risks?

 1. Miscarriage - In women with poorly controlled diabetes, the risk of miscarriage increases. Risk of miscarriage is increased with increased HbA1c levels

2. Congenital anomalies

 The risk of having fetal abnormalities in diabetic pregnancies is quoted to be 3-8% from different centres. This accounts for 20 - 50% of perinatal deaths and correlates to hyperglycemia in early pregnancy.

 There is a correlation with HbA1c levels. With HbA1c < 6, risk is 3% whereas the risk increases up to 35% with HbA1c > 12. The most common anomalies seen in diabetic pregnancies are cardiac and NTD.

3. Preterm delivery: These are seen in up to 20% of diabetic pregnancies and can sometimes be tricky to manage because of the effect of both steroids and tocolysis on the glycemic control. Steroids for fetal lung maturation must be given and the sugars monitored with a temporary increase in insulin if needed when preterm delivery is anticipated especially because neonates of diabetic moms are at an increased risk of RDS.

Fetal Growth in Diabetes

As mentioned earlier, maternal hyperglycemia causes fetal hyperglycemia. The resulting reactive hyperinsulinemia in the fetus causes the accumulation of subcutaenous fat. As the brain growth is insensitive to insulin, accelerated growth of the trunk alone happens and this is seen as an abdominal circumference measurement in the higher centiles. Post prandial blood sugars rather than fasting sugars correlate better with birth weight and fetal size.

Western data indicates that about 20 – 40% of diabetic moms have babies with birth weight over 90th centile. About 80% of LGA babies will have fetal weight and AC are both above the 90th centile. 

figure: LGA macrosomia

figure: effect of tight control

With extremely tight control of sugars and caloric restriction, some of these fetuses remain SGA and low growth profiles are seen. In such situations, while continuing to maintain glycemic control an increases in caloric intake results in improvement of fetal growth. SGA babies are also seen when there is associated hypertensive disease or diabetic vasculopathy.