Flat glucose response curve during pregnancy and perinatal outcomes: A systematic review and meta‐analysis

BACKGROUND: Gestational diabetes mellitus (GDM) is one of the most frequent metabolic disorders in pregnancy, affecting around 14% of pregnancies globally, and associated with increased risk of maternal and perinatal complications. OBJECTIVE: This study evaluates the association between a flat glucose response curve (FC) during the oral glucose tolerance test (OGTT) in pregnancy and perinatal outcomes. SEARCH STRATEGY: This systematic review and meta-analysis adhered to the PRISMA guidelines. MEDLINE/PubMed, CINAHL, Cochrane Library, Embase, Ovid, Web of Science, and Google Scholar were searched from database inception to May 2, 2026. SELECTION CRITERIA: Eligible studies compared pregnant women with FC with those showing a standard OGTT curve. DATA COLLECTION AND ANALYSIS: The primary outcome was small for gestational age (SGA). Secondary outcomes were macrosomia, hypertensive disorders of pregnancy (HDP), primary caesarean delivery (PCD), vaginal delivery, Apgar score <7-8 at 5 min, neonatal intensive care unit (NICU) admission, and neonatal sex. Odds ratios (ORs) with 95% confidence intervals (CIs) were pooled using fixed-effects models. Study quality was assessed using the NIH Quality Assessment Tool for observational cohort and cross-sectional studies. MAIN RESULTS: Five cohort studies involving 5150 women with FC and 41 898 controls were included. FC was associated with higher risk of SGA (OR 1.21; 95% CI 1.06-1.38; P = 0.005) and lower odds of macrosomia (OR 0.74; 95% CI 0.66-0.83; P < 0.00001), HDP (OR 0.66; 95% CI 0.55-0.80; P < 0.0001), and PCD (OR 0.85; 95% CI 0.77-0.93; P = 0.0005). FC was linked to increased vaginal delivery (OR 1.16; 95% CI 1.06-1.27; P = 0.001). No associations were found for Apgar <7-8 or NICU admission. Male sex was more frequent in the FC group (OR 1.14; 95% CI 1.04-1.24; P = 0.003). CONCLUSION: An FC may represent a distinct metabolic-obstetric phenotype associated with an increased risk of SGA, highlighting the potential prognostic value of OGTT curve morphology beyond conventional gestational diabetes thresholds.