Small fetal abdominal circumference in the second trimester and subsequent low maternal plasma glucose after a glucose challenge test is associated with the delivery of a small-for-gestational age neonate

Objectives: To evaluate the predictive value of a combination of the 1 h 50-g glucose challenge test (GCT) and second-trimester ultrasound measurement of fetal abdominal circumference (AC) in identifying patients who will go on to deliver small-for-gestational age (SGA) neonates. The individual predictive power of these tests has been indicated by previous studies, but this study examines the combined use of these indicators in predicting SGA.

Methods: This retrospective cohort study included 576 consecutive patients with singleton gestations examined over a 3-year period. Patients' electronic medical records were abstracted to obtain the result of the GCT, the fetal AC measured by ultrasound examination between 18 and 22 weeks' gestation, and the birth weight. SGA and small AC were defined as birth weight or AC < 10(th) percentile for gestational age, according to published nomograms. A low GCT was defined as < 100 mg/dL. P < 0.05 was considered significant.

Results: The prevalence of SGA in the study population was 8.7% (50/576). The frequency of SGA neonates was significantly higher in patients with a low GCT (27/207) in the second trimester than in those with a normal GCT (23/369) (13% vs. 6.2%, P = 0.005). Similarly, the frequency of SGA neonates was higher among patients with fetal AC < 10(th) percentile than among those with a normal fetal AC on second-trimester ultrasound examination (17% vs. 8%, P = 0.08), although this difference did not reach statistical significance. Of interest, among patients with both a small fetal AC and a low GCT the incidence of SGA neonates was 32% (6/19), but there were no SGA neonates among those with a small AC and normal GCT (0/17) (P = 0.014). Among patients with a small fetal AC the sensitivity of using low GCT to predict subsequent delivery of a SGA neonate was 100%, with a specificity of 57%, positive predictive value 32% and negative predictive value 100%.

Conclusions: Small AC on routine second-trimester anomaly sonogram should trigger a closer evaluation of maternal GCT. If the GCT is also low, more intensive surveillance for the possible development of a SGA infant is warranted.