Preconception HbA_1cLevels in Adolescents and Young Adults and Adverse Birth Outcomes

Importance: Subclinical hyperglycemia before pregnancy may be associated with the likelihood of maternal morbidity but is understudied among young people. Objective: To explore the association of preconception hemoglobin A1c (HbA1c) levels among adolescents and young adults with risk of gestational diabetes at first live birth. Design, Setting, and Participants: This retrospective cohort study used linked 2009 to 2017 birth registry, hospital discharge, and New York City Department of Health A1C Registry data for birthing individuals aged 10 to 24 years with no history of diabetes and at least 1 preconception HbA1c test in New York, New York. Statistical analysis was performed from August to November 2022. Exposure: Preconception HbA1c values categorized as no diabetes (HbA1c <5.7%) or prediabetes (HbA1c ≥5.7% to <6.5%). Main Outcomes and Measures: The primary outcome was gestational diabetes at first birth. Secondary outcomes included hypertensive disorders of pregnancy, preterm birth, cesarean delivery, and macrosomia. Log binomial regression was used to estimate the relative risk (RR) of gestational diabetes at first birth by preconception HbA1c level, adjusting for prepregnancy characteristics. The optimal HbA1c threshold for gestational diabetes was examined using receiver operating curve regression. Results: A total of 14302 individuals (mean [SD] age, 22.10 [1.55] years) met study eligibility criteria. Of these, 5896 (41.0%) were Hispanic, 4149 (29.0%) were Black, 2583 (18.1%) were White, 1516 (10.6%) were Asian, and 185 (1.3%) had other or unknown race and ethnicity. Most (11407 individuals [79.7%]) had normoglycemia before pregnancy, and 2895 individuals (20.2%) had prediabetes. Adjusting for prepregnancy characteristics, those with preconception prediabetes had more than twice the risk of gestational diabetes vs those with normoglycemia (adjusted RR [aRR], 2.21; 95% CI, 1.91-2.56). Preconception prediabetes was associated with small increases in the likelihood of a hypertensive disorder of pregnancy (aRR, 1.18; 95% CI, 1.03-1.35) and preterm delivery (aRR, 1.18; 95% CI, 1.02-1.37). The aRRs for cesarean delivery (aRR, 1.09; 95% CI, 0.99-1.20) and macrosomia (aRR, 1.13; 95% CI, 0.93-1.37) were increased but not statistically significant. The optimal HbA1c threshold to identify gestational diabetes among adolescents and young adults was 5.6%. The threshold did not vary by obesity status but was slightly lower among Hispanic individuals (HbA1c of 5.5%). Conclusions and Relevance: In this study of adolescents and young adults with at least 1 preconception HbA1c test, prediabetes was associated with increased likelihood of maternal cardiometabolic morbidity at first birth. Efforts to optimize cardiometabolic health before pregnancy may avert excess maternal risk.