Mothers with diabetes have a more than four times greater risk of still birth than pregnant women without the condition, a study* published in Diabetologia has found.
High maternal blood sugar and BMI were risk factors, and babies at the lowest and highest weights were most at risk, the research found.
While still births have been decreasing among the general obstetric population over recent years, there has been no improvement seen in women with diabetes. While one third of stillbirths in mothers with diabetes occur close to term and might be influenced by policy on delivery, the majority occur before 37 weeks so finding better ways of detecting babies at risk is critical, the researchers from the University of Glasgow said.
For the study they linked maternity records from the Scottish Morbidity Record 02 (SMR02) – a database containing clinical information on all birth episodes across Scotland – to data from Scottish Care Information-Diabetes (SCI-Diabetes) – a database containing patient demographics and clinical information on diabetes diagnosis, complications and management.
They identified 5,392 singleton babies born to 3,847 mothers with diabetes (3,778 babies to 2,582 mothers with type 1 diabetes; and 1,614 babies to 1,265 mothers with type 2 diabetes), among which stillbirth rates were 16.1 per 1000 births in type 1 and 22.9 per 1000 births in type 2, compared with 4.9 per 1,000 births in the general population.
The researchers found that maternal blood glucose level is the key modifiable risk factor for stillbirth in pregnant women with diabetes. Women with type 1 diabetes who suffered stillbirth were seen to have higher average blood glucose levels at all stages of pregnancy, and for type 2 diabetes pre-pregnancy blood glucose levels, rather than levels during pregnancy, appeared to be a more important predictor of stillbirth. Another risk factor for stillbirth in mothers with type 2 diabetes was high maternal BMI.
In the general obstetric population, fetal growth restriction, whereby the unborn baby is smaller than it should be, is the strongest indicator of stillbirth risk. The researchers found a similar association in this group, particularly for type 1 diabetes. Larger than gestational age is a risk factor in the general population, and this was found to be also the case in type 2 diabetes. Fetal overgrowth relates to maternal hyperglycaemia in later pregnancy, in this study the researchers noted that, even for mothers with the lowest blood glucose levels, the child's birth weight was considerably higher than that of the general population.
"Achievement of near normal blood sugar levels remains key to reducing risk," the researchers said, recommending "methods of supporting women to improve blood glucose levels in pregnancy, along with programmes to optimise weight before pregnancy." As stillbirth risk is high at full term, the authors recommend that "until more accurate assessment of risk during pregnancy becomes available, earlier delivery may be considered an attractive option."
Routine early delivery is generally recommended for mothers with diabetes, with National Institute for Health and Care Excellence (NICE) guidelines suggesting delivery in the 37th or 38th week. Compared to the general population, an increased risk of stillbirth for women with diabetes is seen at all stages of pregnancy, and previous studies have shown that at full term the higher risk is at least five-fold. In this study a third of the stillbirths occurred at term.
"It would seem then that earlier delivery would be a sensible approach," said the researchers. "However, because of potential issues with early delivery, including respiratory distress syndrome as a result of inadequate lung development, we suggest that the increased risk of neonatal morbidity needs to be more formally explored before recommendations for optimal timing of delivery are made, particularly where mothers are managing to obtain almost normal blood glucose levels."
Unexpectedly, within this study a high proportion of stillborn infants (81%) were male among the mothers with type 2 diabetes. Previous studies indicate that male foetuses are more vulnerable in utero, with an increased risk of stillbirth of about 10% comparted to female infants.
*Mackin ST, Nelson SM, Wild SH, et al. Factors associated with stillbirth in women with diabetes. Diabetologia, 29 July 2019. DOI:10.1007/s00125-019-4943-9