Association Between a Flat Oral Glucose Tolerance Test Pattern and Small-for-Gestational-Age Infants: A Retrospective Cohort Study

Objective: To evaluate the clinical significance of a flat oral glucose tolerance test (OGTT) pattern and its association with obstetric and perinatal outcomes, focusing on fetal growth. Methods: This retrospective cohort study was conducted at a tertiary referral center between January 2023 and November 2025. A total of 1198 women who underwent a two-step OGTT between 24 and 32 weeks of gestation were screened, and 685 eligible participants were included. A flat OGTT pattern was defined as fasting glucose < 95 mg/dL with all postprandial values < 100 mg/dL. The primary outcome was small-for-gestational-age (SGA); secondary outcomes included fetal growth restriction (FGR) and other obstetric outcomes. Logistic regression analyses were performed to assess independent associations. Results: Thirty-nine women (5.7%) exhibited a flat OGTT pattern. These pregnancies were characterized by a markedly attenuated postprandial glycemic response and lower fasting glucose levels. Most maternal and neonatal outcomes were similar between groups. However, SGA was significantly more frequent in the flat OGTT group (20.5% vs. 6.7%, p = 0.001). In multivariable analysis, a flat OGTT pattern remained independently associated with SGA (aOR 4.05, 95% CI 1.70–9.68, p = 0.002). Both SGA and FGR were more frequent among women with a flat OGTT pattern, although the association appeared stronger for SGA. Conclusions: A flat OGTT pattern appears to represent a distinct glycemic response characterized by an attenuated postprandial glucose response and lower fasting glucose levels. Although this pattern was not associated with a generalized increase in adverse obstetric or neonatal outcomes, it was associated with an increased risk of small-for-gestational-age infants.