Pregnant women with type 1 diabetes are at greater risk of preterm birth

Reviewed by Alina Shrourou, B.Sc. (Editor)Apr 23 2019

Pregnant women with type 1 diabetes are at increased risk of delivering their baby prematurely. The risk increases as blood sugar levels rise, however women who maintain the recommended levels also risk giving birth prematurely. These are the findings from researchers at Karolinska Institutet and the Sahlgrenska Academy in Sweden, published in Annals of Internal Medicine.

In a previous study published in The BMJ, the research group showed that pregnant women with type 1 diabetes were at an increased risk of having babies with heart defects. Now, a new study is published that shows how women with type 1 diabetes have an increased risk of giving birth prematurely.

"High long-term blood sugar, so called HbA1c, during pregnancy is linked to an increased risk for complications, including preterm birth. The risk is highest amongst those with HbA1c levels above 8-9 per cent (approximately 60-70 mmol/mol), but even those who maintain their HbA1c (below 6.5 per cent, equivalent to <48 mmol/mol) are at an increased risk of giving birth prematurely," explains Jonas F. Ludvigsson, Professor at the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet and Senior Physician at the Department of Pediatrics at örebro University Hospital.

Risk increases as blood sugar levels rise

The study involved linking the Swedish Medical Birth Register (MFR) to the Swedish National Diabetes Register (NDR) for the years 2003 to 2014. Researchers identified 2,474 infants born to women who recorded long-term glycosylated hemoglobin levels (HbA1c) during pregnancy. These were compared to 1.16 million infants born to women without diabetes.

Approximately 22 per cent of infants born to women with type 1 diabetes were born prematurely, which can be compared to below five per cent of infants born to women without type 1 diabetes. 37 per cent of women with type 1 diabetes and an HbA1c level above 9 per cent gave birth prematurely. Yet even 13 per cent of those with adhering to the current recommendations for blood sugar gave birth too early.

"This is the first study large enough to demonstrate a clear relationship between different HbA1c levels and preterm birth. Our study has been conducted nationally and thus provides a result that can be applied to the average woman with type 1 diabetes," says Jonas F. Ludvigsson.

Increased risk of other complications

The study also found an increased risk of these newborns being "large for gestational age", being injured during childbirth, experiencing respiratory problems, low blood sugar and suffering from lack of oxygen ("asphyxia") in addition to higher neonatal mortality rates amongst those exposed to high blood sugar during pregnancy. Also the risk of stillbirth was linked to HbA1c levels in pregnant women with type 1 diabetes.

"Now, we want to examine the long-term outcome of these children." says Jonas F. Ludvigsson.