Choice of Formula and Accuracy of Fetal Weight Estimation in Small‐for‐Gestational‐Age Fetuses

Abstract

Objectives The purpose of this study was to identify the most accurate sonographic models for fetal weight estimation in specific subgroups of small‐for‐gestational‐age (SGA) fetuses. Methods We conducted a retrospective study of women who delivered an SGA neonate and underwent a sonographic estimation of fetal weight within 7 days of delivery in a single tertiary center (n = 370). The accuracy of fetal weight estimation was compared for 33 sonographic models (27 nontargeted and 6 targeted SGA– or low‐birth‐weight–specific models) in specific subgroups of SGA fetuses: early versus late SGA, asymmetric versus symmetric, and presence of Doppler abnormalities. Results A wide variation in the accuracy of the different models was found (systematic error, −12.5% to 15.1%; random error, 7.8% to 15.5%). Most nontargeted models tended to systematically overestimate the weight of SGA fetuses. The best performing model in the overall SGA group was the targeted model of Scott et al (J Ultrasound Med 1996; 15:669–672; systematic error ± random error, −2.8% ± 8.3%). However, the optimal models varied for different subgroups of SGA fetuses, and in most cases the targeted models were the most accurate. An approach that used the optimal model for each subgroup of SGA fetuses compared with the uniform use of the model of Scott et al for all SGA fetuses was associated with a lower systematic error (−0.38% versus −2.8%; P < .001) and a higher proportion of weight estimations within 5%, 10%, and 15% of birth weight (48.4% versus 40.8%; P= .038; 78.6% versus 71.4%; P= .022; 95.1% versus 89.2%; P = .003, respectively). Conclusions Sonographic models in current use for fetal weight estimation in SGA fetuses have significant errors, and their performance varies for specific subgroups of SGA fetuses. An approach that uses subgroup‐specific models may improve the accuracy of weight estimation among SGA fetuses.

In vivo placental MRI shape and textural features predict fetal growth restriction and postnatal outcome

“…Similarly, clinically available tools have various limitations in the estimation of BW, particularly for infants at the two ends of the spectrum of normal BW distribution (i.e., SGA and large for gestational age infants). While the reasons are not well understood, it has been shown that most fetal weight estimation methods perform poorly when dealing with SGA fetuses . Previous studies have shown that methods specifically designed for SGA populations work better than generic ones .…”

“…While the reasons are not well understood, it has been shown that most fetal weight estimation methods perform poorly when dealing with SGA fetuses . Previous studies have shown that methods specifically designed for SGA populations work better than generic ones . Moreover, even with SGA specific methods, those that consider SGA as a homogeneous group tend to overestimate BW while the opposite trend is observed for SGA sub‐group specific approaches …”

“…6 Sonographic estimations of fetal weight at the time of delivery and prediction of birth weight (BW) can vary by over 15%. 6 Moreover, for SGA fetuses, estimation of fetal weight is even more problematic, with sensitivity as low and variable as 35-57%. 7 Alternate methods for predicting BW include in vivo two-dimensional (2D) and threedimensional (3D) sonography of placental volume and surface area.…”

Fetal Biometry and Doppler Study for the Assessment of Perinatal Outcome in Stage I Late-Onset Fetal Growth Restriction

“…Interestingly, among those with normal Doppler, 45.9 and 13.3% of cases in G1 and G2, respectively, turned out to have a neonatal birth weight superior to that established to be considered FGR [9]. On these subgroups, vaginal delivery rate exceeded 90% on the first group and came close to it on the second.…”

Evaluating the accuracy and precision of sonographic fetal weight estimation models in extremely early‐onset fetal growth restriction

“…Other models have been developed in appropriately grown and small‐for‐gestational‐age (SGA) populations and preterm populations but have never been directly compared with one another in an eFGR cohort. Previous research has suggested that the choice of model in an SGA population may depend on other factors, such as gestation, symmetrical/asymmetrical growth or Doppler abnormalities …”