Introduction: Antenatal screening of small for gestational age (SGA) neonates is a clinical challenge, with many cases going undetected. We aimed to evaluate the predictive value of sonographic screening at second and early third trimester in predicting SGA neonates.
Methods: This was a retrospective cohort study including women with singleton pregnancies who delivered at term in a single referral center in 2014. Two cohorts were included: 1) sonographic estimation of fetal weight (EFW) performed at routine anatomy scan (18-24 weeks) and 2) sonographic EFW at third trimester (28-34 weeks). EFW percentiles were tabulated using Hadlock IV and Kramer formulas. Birth weight (BW) percentiles were determined by Kramer curve. Linear regression was used to generate a prediction model for BW percentiles based on EFW percentiles. Predictive accuracy of multiple EFW percentiles for BW <10th and <5th percentiles were calculated.
Results: In total, 698 and 1039 women were included in the second and third trimester cohorts, respectively. At the second trimester, EFW percentile was significantly yet weakly correlated with BW percentile (r=0.27, p<0.001). The area under the ROC curve for the prediction of BW <10th and <5th percentiles were 0.64 and 0.65, respectively. Negative and positive predictive values of different percentile cut-offs are presented in Table 1. At the third-trimester, EFW percentiles according to both Hadlock and Kramer curves were moderately correlated with BW percentile (r=0.56 and r=0.56, respectively). The area under the ROC curve for prediction of BW <10th and < 5th percentiles was similar, 0.79 for both Hadlock and Kramer curves. The 10th percentile cut-off yielded positive and negative predictive values of 75% and 88.4%, respectively, for the prediction of SGA (Table 2).
Conclusion: While second trimester sonographic screening poorly predicts SGA neonates, early third trimester screening has a moderate predictive accuracy. The traditional cut-off of the 10th percentile is the most appropriate.
Amir Aviram– MFM Specialist, Sunnybrook Health Sciences Centre, University of Toronto
Nir Melamed– MFM Specialist, Sunnybrook Health Sciences Centre, University of Toronto
Mara Carson– Research assistant, Sunnybrook Health Sciences Centre, University of Toronto
Rebecca Jackson– Quality Improvement Specialist, Sunnybrook Health Sciences Centre, University of Toronto
Jon Barrett– Chief of Maternal-Fetal Medicine at Sunnybrook Health Sciences Centre, Sunnybrook Health Sciences Centre, University of Toronto
Elad Mei-Dan– MFM Specialist, North York General Hospital