High HbA1c Levels Linked to Pregnancy Risks

For pregnant women with diabetes mellitus some particular challenges exist for both mother and child. If the woman has diabetes as an intercurrent disease in pregnancy, it can cause early labor, birth defects, and larger than average infants.

High blood sugar levels are harmful to the mother and her fetus. Experts advise diabetics to maintain blood sugar level close to normal range for two to three months before planning for pregnancy. Managing blood sugar close to normal before and during pregnancy helps to protect the health of mother and the baby.


Maternal type 1 diabetes (T1D) has been linked to preterm birth and other adverse pregnancy outcomes. Scientists at the Karolinska Institute (Solna, Sweden) and their associates examined how these risks vary with glycated hemoglobin (or HbA1c) levels. They examined preterm birth risk according to periconceptional HbA1c levels in women with T1D. In a population-based cohort study carried out from 2003 to 2014 and they followed 2,474 singletons born to women with T1D and 1,165,216 reference infants born to women without diabetes. Measurement for the study included risk for preterm birth (<37 gestational weeks), secondary outcomes were neonatal death, large for gestational age, macrosomia, infant birth injury, hypoglycemia, respiratory distress, 5-minute Apgar score less than 7, and stillbirth.

The investigators reported that preterm birth occurred in 552 (22.3%) of 2,474 infants born to mothers with T1D versus 54,287 (4.7%) in the infants born to mothers without diabetes. The incidence of preterm birth was 13.2% in women with a periconceptional HbA1c level below 6.5% (adjusted risk ratio [aRR] versus women without T1D, 2.83), 20.6% in those with a level from 6.5% to less than 7.8% (aRR, 4.22), 28.3% in those with a level from 7.8% to less than 9.1% (aRR, 5.56) and 37.5% in those with a level of 9.1% or higher (aRR, 6.91). The corresponding aRRs for 320 medically indicated preterm birth were 5.26, 7.42, 11.75, and 17.51, respectively. The corresponding aRRs for 223 spontaneous preterm birth were 1.81, 2.86, 2.88, and 2.80, respectively.

Increasing HbA1c levels were associated with the study's secondary outcomes: large for gestational age, hypoglycemia, respiratory distress, low Apgar score, neonatal death, and stillbirth. Jonas F. Ludvigsson, MD, PhD, a professor of pediatrics and lead author of the study, said, “This is the first study large enough to demonstrate a clear relationship between different hemoglobin A1C (Hb A1C) 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.” The study was published on April 23, 2019, in the journal Annals of Internal Medicine.

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Karolinska Institute