Midtrimester Ultrasound Predictors of Small-for-Gestational-Age Neonates

Objectives: To determine whether a specific estimated fetal weight (EFW) or abdominal circumference (AC) measurement percentile at the 18-to 24-week ultrasound (US) examination is associated with a small-for-gestational-age (SGA) neonate.

Methods: A retrospective case-control study was conducted including women with uncomplicated singleton gestations who delivered a term SGA neonate identified as having a birth weight (BW) below the 10th percentile on the Olsen growth curve and had an 18- to 24-week US examination in our database. The study period was October 2011 to January 2018. A similar number of control charts were requested randomly over the same time with BW in the 10th to 90th percentiles, all which had an 18-to 24-week US examination in our database. After all neonates meeting BW criteria were identified, a chart review was performed to specifically evaluate biometric parameters from the US at 18 to 24 weeks to determine a potential correlation with the EFW percentile and AC percentile. Pregnancy, neonatal outcomes, and maternal demographic characteristics were collected.

Results: A total of 549 term neonates with a BW below the 10th percentile, and 593 control term neonates with BW in the of 10th to 90th percentiles were reviewed. Our analyses revealed that the AC and EFW percentiles were poor predictors of BW (<10th percentile; areas under the receiver operating characteristic curves, 0.68 and 0.69, respectively). A similar low ability of AC and EFW to predict BW below the 5th percentile was noted.

Conclusions: (1) No tipping point or cutoff for the EFW or AC percentile at the 18- to 24-week US examination was identified to predict a term SGA neonate. (2) These data are helpful when counseling women in midgestation about specific parameters, their importance, and the potential need for follow up imaging.