Elevated hemoglobin A1c (HbA1c) before conception is associated with increased risk for maternal morbidity and mortality among women without preexisting diabetes, according to study results published in PLOS Medicine.

Diabetes and obesity have consistently been associated with adverse pregnancy outcomes, but limited data are available on the association between HbA1c and severe maternal morbidity and mortality. The goal of the current study was to explore the association between elevated preconception HbA1c and severe maternal morbidity and mortality among individuals with and without preexisting diabetes.

The population-based cohort study included 31,225 women aged 16 to 50 who gave birth between 2007 and 2015 in Ontario, Canada, and who had HbA1c measured within 90 days before conception.

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Of all pregnancies included in the study, 682 (2.2%) resulted in severe maternal morbidity or death from 23 weeks’ gestation up to 42 days postpartum, which was the study’s primary outcome. For each 0.5% absolute increase in HbA1c, the adjusted relative risk (RR) was 1.16 (95% CI, 1.13-1.18; P <.001) for this period and the risk from index birth up to 42 days postpartum was 1.11 (95% CI, 1.07-1.16; P <.001).

The adjusted RR was higher among individuals with (RR, 1.11; 95% CI, 1.07-1.14; P <.001) and without (RR, 1.15; 95% CI, 1.02-1.29; P <.001) known prepregnancy diabetes.

When stratified by cutoffs for HbA1c, the adjusted RR for severe maternal morbidity or mortality was 1.31 (95% CI, 1.06-1.62; P =.01) at a prediabetic HbA1c of 5.8% to 6.4% and 2.84 (95% CI, 2.31-3.49; P <.001) at a diabetic HbA1c of >6.4% compared with an HbA1c of <5.8%. Among individuals without diagnosed preconception diabetes, only women with an HbA1c of >6.4% had significantly increased risk for several maternal morbidity or mortality (adjusted RR, 3.25; 95% CI, 1.76-6.00; P <001).

The study had several limitations, according to the researchers, including potential selection bias for less healthy women and missing body mass index data for many women.

“An elevated preconception [HbA1c] is associated with a higher risk of [severe maternal morbidity] or death among women without known diabetes, and below thresholds commonly used to diagnose [diabetes],” concluded the researchers.


Davidson AJF, Park AL, Berger H, et al. Risk of severe maternal morbidity or death in relation to elevated hemoglobin A1c preconception, and in early pregnancy: a population-based cohort study. PLoS Med. 2020;17(5):e1003104.