Prenatal Ultrasonographic Markers of Macrossomia and C-Peptide in Gestational Diabetes Mellitus: A Prospective Cohort Study

<b>Objective:</b> To investigate the association between prenatal ultrasonographic markers of macrossomia and C-peptide, a neonatal hyperinsulinemia marker, in pregnancies complicated by gestational diabetes mellitus (GDM), with a focus on fetal adipose tissue thickness, liver length, and interventricular septal thickness. <b>Methods</b>: This prospective cohort study included 223 pregnant women followed from 28 to 36 weeks of gestation in two referral centers in Brazil. The GDM group and matched controls underwent serial ultrasound assessments of fetal biometry, including thigh, abdominal, and subscapular skinfolds, fetal liver length, and interventricular septum thickness. Neonatal hyperinsulinemia was assessed using umbilical cord C-peptide levels. Statistical analyses included <i>t</i>-tests, chi-square tests, correlation analyses, and multivariate logistic regression. <b>Results</b>: Fetuses of mothers with GDM exhibited significantly greater abdominal [t(221) = -3.999, <i>p</i> < 0.01] and subscapular [t(221) = -2.502, <i>p</i> = 0.02] skinfolds, liver length [t(221) = -3.785, <i>p</i> < 0.01], and interventricular septum [t(221) = -4.781, <i>p</i> < 0.01] thickness. However, umbilical cord C-peptide levels did not differ significantly between groups [t(189) = -1.724, <i>p</i> = 0.09]. Only weak correlations were found between fetal ultrasound markers and C-peptide levels. Among all parameters, subcutaneous tissue thickness showed the highest (ρ = 0.30), though still limited, predictive value. <b>Conclusions:</b> Fetuses of mothers with GDM demonstrated increased measures of liver length, subscapular adiposity, and interventricular septal thickness compared to controls. However, these prenatal biometric markers showed weak correlations with neonatal C-peptide levels.