Does the number of abnormal values in the oral glucose tolerance test impact pregnancy outcomes?

Gestational diabetes mellitus (GDM) affects over 10% of pregnancies worldwide, leading to various maternal and neonatal complications. The American College of Obstetricians and Gynecologists (ACOG) recommends a two-step diagnostic approach using the Glucose Challenge Test (GCT) and the oral glucose tolerance test (OGTT), which can yield between 0 and 4 abnormal values (AbVs). The primary objective of this study was to evaluate the association between the number of AbVs in the OGTT and the risk of GDMA2 - gestational diabetes mellitus requiring pharmacological treatment (insulin or oral glucose-lowering agents) - compared with GDMA1, which is diet-controlled. Secondary outcomes included assessing the relationship between the number of AbVs and adverse maternal and neonatal outcomes, considering its impact on the course of pregnancy, delivery, maternal health, and neonatal outcomes.

This retrospective cohort study included all pregnant women who underwent OGTT between the years 2015 and 2022, and diagnosed with GDM, at our department. The study cohort was divided into four groups based on the number of AbVs in the OGTT: one AbV, two AbVs, three AbVs and four AbVs group. Maternal characteristics and pregnancy outcomes were compared between these groups.

A total of 1821 women diagnosed with GDM following the diagnostic OGTT were included in the analysis. The distribution of abnormal OGTT AbVs was as follows: one AbV (36.95%), two AbVs (43.71%), three AbVs (16.09%), and four AbVs (3.24%). Presence of GDMA2 varied significantly among groups (p < 0.001), with higher occurrence correlating with increased AbVs. Maternal outcomes differed across the AbV groups in induction of labor (p < 0.001), episiotomy (p = 0.006), and maternal composite outcomes (p = 0.011). Neonatal outcomes also differed across the AbV groups, with differences in gestational age at delivery (p = 0.007) and Apgar score < 7 (p = 0.021). Logistic regression adjusted for confounders revealed that the number of AbVs (aOR 1.2, 95% CI 1.01-1.42) and maternal BMI (aOR 1.07, 95% CI 1.05-1.1) were significantly associated with GDMA2.

An elevated number AbVs indicates challenges in glycemic control through dietary measures alone, necessitating potential medical interventions. An increased number of AbVs in OGTT was associated with GDMA2 and induction of labor. Differences were also observed across groups in episiotomy rates and Apgar < 7, although Apgar < 7 did not show a consistent positive correlation with the number of AbVs. From the study results we can infer that OGTT serves not only as a diagnostic tool for GDM but also enables healthcare practitioners to enhance their awareness of potential adverse outcomes for both the mother and neonate through meticulous analysis of AbVs.