Accelerated Fetal Growth Prior to Diagnosis of Gestational Diabetes Mellitus: A Prospective Cohort Study of Nulliparous Women

To determine whether fetal overgrowth precedes the diagnosis of gestational diabetes mellitus (GDM) and to quantify the interrelationships among fetal overgrowth, GDM, and maternal obesity. We conducted a prospective cohort study of unselected nulliparous women and performed ultrasonic measurement of the fetal abdominal circumference (AC) and head circumference (HC) at 20 and 28 weeks of gestational age (wkGA). Exposures were diagnosis of GDM ≥28 wkGA and maternal obesity. The risk of AC >90th and HC-to-AC ratio 90th percentile (adjusted relative risk 2.05 [95% CI 1.37-3.07]) and HC-to-AC ratio 90th (4.52 [2.98-6.85]) and approximately threefold risk of HC-to-AC ratio 90th percentile at 28 weeks was associated with an approximately fourfold risk of being large for gestational age at birth. Diagnosis of GDM is preceded by excessive growth of the fetal AC between 20 and 28 wkGA, and its effects on fetal growth are additive with the effects of maternal obesity.