"This confirms previous findings that there is a higher risk of birth defects, primarily of the heart," says Professor Ludvigsson. "The risk of birth defects is especially sensitive to factors during early pregnancy, and here blood glucose plays a vital part."
For the study, the investigators cross-referenced the National Diabetes Register with the National Patient Register and the Medical Birth Registry and compared 2,458 living newborns of mothers with T1D with 1,159,865 babies of mothers without diabetes.
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"Since this is an observational study no definitive conclusions can be drawn regarding causality. We are now planning to make further investigations in the field," write the authors.
The study demonstrates a clear correlation between elevated levels of blood glucose (HbA1c) in the mother and the risk of heart defects in her baby. However, even those women who followed the current guidelines had a higher, albeit still small, risk of heart defects.
Key Findings:
- 3.3 percent of pregnant women with type 1 diabetes and blood glucose levels within the recommended span gave birth to a baby with a heart defect. The corresponding figure for women without diabetes was 1.5 percent.
- Pregnant women with type 1 diabetes who had very high blood glucose levels (an HbA1c reading of 9.1 percent or higher) were at much greater risk.
- 122 cases of major cardiac defects were observed among 2458 infants of mothers with type 1 diabetes. Compared with 15 cases of major cardiac defects per 1000 infants of mothers without diabetes.
- 50 cases of major non-cardiac defects were observed among infants of mothers with type 1 diabetes. Compared with 18 cases of major non-cardiac defects per 1000 infants of mothers without diabetes.
"The reason why the risk of deformity can be linked to blood glucose levels in early pregnancy is that it is then that the fetus's organs develop. Also, many women aren't aware that they're pregnant during the first few months," said Dr. Ludvigsson.
This, he stresses, is why women must know about the dangers before trying to have children.
"There's an opportunity here for women to influence the risk of their baby developing a heart defect by keeping their blood glucose levels low. Yet we as doctors also know that many pregnant women struggle valiantly to keep their blood glucose down, as it is no easy task. The potential benefit of intensified insulin treatment to reduce the risk of heart defects should also be weighed against possible risks with hypoglycemia in the mother and fetus," says Professor Ludvigsson
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