The ‘Behind the Headlines’ service from NHS Choices has featured an assessment of press reports that mothers-to-be with diabetes have a high risk of giving birth to children with congenital abnormality (as reported by The Guardian and others, 6th February 2012).

The assessment discusses the evidence that the reports are based on, including the type of research, what it involved, the basic results, and how the researchers interpreted their findings.  It notes that the study is a cohort study that was funded by the Department of Health, Diabetes UK, the Healthcare Quality Improvement Partnership, and the four primary care trusts in northeast England, and it has been published in the medical journal Diabetologica.  Researchers collected data on 401,149 pregnancies, 1,677 of which were in women with pre-existing diabetes (78.4% type 1).  Overall, 9,488 pregnancies were affected by at least one major birth defect, 129 of which were in women with diabetes.  This worked out at a rate of 71.6 per 1,000 pregnancies for those women with diabetes – a rate 3.8 times higher than that seen in women without diabetes (this was for non-chromosomal major birth defects; there was no increased risk of birth defects caused by chromosomal abnormalities).    

When looking at specific factors linked to the risk of birth defects, the researchers found that women who had worse blood sugar control at around the time of conception were at increased risk of having babies with birth defects. Each increase of 1% in HbA1c over 6.3% was associated with a 30% increase in the odds of birth defects (odds ratio [OR] 1.3, 95% CI 1.2 to 1.4). Women who already had kidney problems as a result of their diabetes also had an increased risk of having babies with birth defects (OR 2.5, 95% CI 1.1 to 5.3).

The authors comment that this study provides further evidence on what is already known – maternal diabetes increases the risk of birth abnormalities – and helps to quantify the size of the association.  They discuss a few points that should be taken into consideration; for example the reliance on registry data (possible omissions or data inaccuracies), the possibility of unknown confounders, and it does not provide any information on the risks associated with gestational diabetes.  They refer to NICE guidance on this topic that addresses this known risk – please see the link below for details.