The purpose of this study was to examine the relationship between newborn macrosomia and plasma glucose profile in both a "glucose challenge test (GCT)-positive oral glucose tolerance test (OGTT)-negative" group (n = 113) and a gestational diabetes mellitus (GDM) group (n = 50). We examined 1) plasma glucose concentrations following a positive screen 50-g GCT (n = 163), 2) glucose concentrations following a 100-g OGTT (n = 163), and 3) the average fasting (AF) and 2-hour postprandial (APP) plasma glucose concentrations in the treated GDM group (n = 46). It was a case-control study with macrosomia vs. non-macrosomia in the ratio of 1:4. Macrosomia was analyzed by both birthweight > 4,000 g and gender-specific birthweight > 90th percentile for gestational age criteria. The GCT and the OGTT were performed between 26 and 30 weeks of pregnancy. The results demonstrated no significant impact of plasma glucose values from GCT, OGTT, AF, or APP on macrosomia in both "GCT-positive OGTT-negative" and GDM (treated) groups. Further, the screening and diagnostic plasma glucose concentrations were not related to macrosomia in both "GCT-positive OGTT-negative" and GDM groups. We found a difference of 0.6 mmol/liter in the maternal AF and APP glucose concentrations between mothers of macrosomic versus non-macrosomic newborns in the treated (diet or diet+insulin) GDM group. The clinical relevance of this difference remains to be explored. Our study provides a different methodological and analytic perspective in examining macrosomia versus non-macrosomia in the "GCT-positive OGTT-negative" and the GDM groups using univariate and multivariate analyses.