Hemoglobin A1c Trajectories During Pregnancy and Adverse Outcomes in Women With Type 2 Diabetes: A Danish National Population-Based Cohort Study

OBJECTIVE To identify and characterize groups of pregnant women with type 2 diabetes with distinct hemoglobin A1c (HbA1c) trajectories across gestation and to examine the association with adverse obstetric and perinatal outcomes. RESEARCH DESIGN AND METHODS This was a retrospective Danish national cohort study including all singleton pregnancies in women with type 2 diabetes, giving birth to a liveborn infant, between 2004 and 2019. HbA1c trajectories were identified using latent class linear mixed-model analysis. Associations with adverse outcomes were examined with logistic regression models. RESULTS A total of 1,129 pregnancies were included. Three HbA1c trajectory groups were identified and named according to the glycemic control in early pregnancy (good, 59%; moderate, 32%; and poor, 9%). According to the model, all groups attained an estimated HbA1c <6.5% (48 mmol/mol) during pregnancy, with no differences between groups in the 3rd trimester. Women with poor glycemic control in early pregnancy had lower odds of having an infant with large-for-gestational-age (LGA) birth weight (adjusted odds ratio [aOR] 0.57, 95% CI 0.40–0.83), and higher odds of having an infant with small-for-gestational age (SGA) birth weight (aOR 2.49, 95% CI 2.00–3.10) and congenital malformation (CM) (aOR 4.60 95% CI 3.39–6.26) compared with women with good glycemic control. There was no evidence of a difference in odds of preeclampsia, preterm birth, and caesarean section between groups. CONCLUSIONS Women with poor glycemic control in early pregnancy have lower odds of having an infant with LGA birth weight, but higher odds of having an infant with SGA birth weight and CM.