A prenatal standard for fetal weight improves the prenatal diagnosis of small for gestational age fetuses in pregnancies at increased risk

Objective: Our aim was to assess diagnostic accuracy in the prediction of small for gestational age (SGA <10th centile) and fetal growth restricted (FGR) (SGA <3rd centile) fetuses using three different sonographic methods in pregnancies at increased risk of fetal growth restriction: 1) fetal abdominal circumference (AC) z-scores, 2) estimated fetal weight (EFW) z-scores according to postnatal reference standard; 3) EFW z-scores according to a prenatal reference standard. Methods: Singleton pregnancies at increased risk of fetal growth restriction seen in two university hospitals between 2014 and 2015 were studied retrospectively. EFW was calculated using formulas proposed by the INTERGROWTH-21st project and Hadlock; data derived from publications by the INTEGROWTH-twenty-first century project and Hadlock were used to calculate z-scores (AC and EFW). The accuracy of different methods was calculated and compared. Results: The study group included 406 patients. Prenatal standard EFW z-scores derived from INTERGROWTH-21st project and Hadlock and co-workers performed similarly and were more accurate in identifying SGA infants than using AC z-scores or a postnatal reference standard. The subgroups analysis demonstrated that EFW prenatal standard was more or similarly accurate compared to other methods across all subgroups, defined by gestational age and birth weight. Conclusions: Prenatal standard EFW z-scores derived from either INTERGROWTH-21 st project or Hadlock and co-workers publications demonstrated a statistically significant advantage over other biometric methods in the diagnosis of SGA fetuses.