High Plasma Glucose Raises Baby Heart-Defect Risk

For many years, physicians have known that women with diabetes face an increased risk of giving birth to babies with heart defects and some studies have also suggested a link between nondiabetic mothers' blood sugar levels and babies' heart defect risk.

One challenge associated with conducting such studies was the fact that maternal blood glucose is not routinely measured in nondiabetic pregnant women. Instead, women typically receive an oral glucose tolerance test halfway through pregnancy to determine whether they have gestational diabetes, but this test is performed well after the fetal heart has formed.

A team of scientists mainly from Stanford University Medical Center (Stanford, CA, USA) studied medical records from 19,107 pairs of mothers and their babies born between 2009 and 2015. The records included details of the mothers' prenatal care, including blood test results and any cardiac diagnoses made for the babies during pregnancy or after birth. The scientists analyzed blood glucose levels from any blood sample collected from the mothers between four weeks prior to the estimated date of conception and the end of the 14th gestational week, just after the completion of the first trimester of pregnancy. These early blood glucose measurements were available for 2,292, or 13%, of women in the study. They also looked at the results of oral glucose tolerance tests (OGTT) performed around 20 weeks of gestation, which were available for 9,511, or just under half, of the women in the study.

After excluding women who had diabetes before pregnancy or who developed it during pregnancy, the results showed that the risk of giving birth to a child with a congenital heart defect was elevated by 8% for every increase of 10 mg/dL in blood glucose levels in the early stages of pregnancy. The mean early glucose value was 96 mg/dL (5.3 mmol/L) in pregnancies without congenital heart disease (CHD) versus 107 mg/dL (6.0 mmol/L) in pregnancies with CHD. The respective mean 1-hour OGTT values were 117 mg/dL (6.5 mmol/L) and 122 mg/dL (6.8 mmol/L).

The findings demonstrate that higher random plasma glucose values measured during early pregnancy correlate with increased risk for congenital heart disease in offspring of mothers who do not have diabetes. Furthermore, plasma glucose measured during early pregnancy was more associated with risk for congenital heart disease in offspring, compared with the OGTT which is often used to risk-stratify pregnancies for fetal-echocardiographic screening.

James R. Priest, MD, an assistant professor of pediatric cardiology and the senior author of the study, said, “Most women who have a child with congenital heart disease are not diabetic. We found that in women who don't already have diabetes or develop diabetes during pregnancy, we can still measure risk for having a child with congenital heart disease by looking at their glucose values during the first trimester of pregnancy.” The study was published on December 15, 2017, in The Journal of Pediatrics.

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Stanford University Medical Center