High blood sugar and BMI in pregnant women with diabetes puts them at greater risk of having a stillbirth.
Researchers from the University of Glasgow found that mothers with pre-pregnancy type 2 diabetes are four times more likely to have a stillbirth than the rest of the population. Women with type 1 diabetes were three times more likely to experience stillbirth.
High blood sugar was found to be a key risk factor. Women with type 1 diabetes were seen to have higher levels of blood glucose throughout pregnancy whereas pre-pregnancy blood sugar levels were found to be a better indicator of stillbirth than pregnancy blood sugar in women with type 2 diabetes.
The researchers said: "Overall efforts to improve blood glucose levels before and during pregnancy remain central. Achievement of near-normal blood sugar levels remains key to reducing risk." They recommend "methods of supporting women to improve blood glucose levels in pregnancy, along with programmes to optimise weight before pregnancy".
The study looked at 5,392 babies born to 3,847 mothers with either type 1 or type 2 diabetes over 18 years. Stillbirth rates were 16.1 per 1,000 births in mothers with type 1 diabetes and 22.9 per 1,000 births in type 2. The rate is 4.9 stillbirths per 1,000 live births in the general population.
Babies at the highest and lowest weights were most at risk of stillbirth in mothers with diabetes. Even in mothers with the lowest blood glucose levels, the child's birth weight was found to be considerably higher on average than that of the general population.
Surprisingly, 81% of babies born stillborn were male, among mothers with type 2 diabetes. Other studies have found that male fetuses are 10% more likely to be stillborn than female fetuses.
Researchers also looked at the timing of birth. Of the more than 3,000 stillborn babies each year in the UK, a third are babies carried for 37 weeks or more and considered healthy prior to death. It is currently recommended that women with diabetes deliver early, in the 37thor 38th week as the risk of stillbirth at full term is at least five times higher than for the rest of the population. A third of the stillbirths in the study occurred at full term.
The authors said: "it would seem then that earlier delivery would be a sensible approach", but cited other risks with early delivery such as "respiratory distress syndrome as a result of inadequate lung development", and encouraged further investigation into the timing of birth in women with diabetes.
This study was published in Diabetologia.