Evaluating the Need for Multiple Ultrasound Measurements for Accurate Prediction of Birthweight Using Estimated Fetal Weight.

OBJECTIVES

To evaluate whether averaging replicate fetal biometry measurements during an examination improves estimated fetal weight (EFW) accuracy for predicting birthweight compared with a single set and to assess how variability in fetal biometric measurements changes across gestation.

METHODS

Secondary analysis of the Eunice Kennedy Shriver National Institute of Child and Health and Human Development (NICHD) Fetal Growth Studies-Singletons. At each study visit, fetal head circumference (HC), abdominal circumference (AC), and femur length (FL) were measured in triplicate to compute EFW at each of 6 study visits (0-5). Variability among replicates was assessed across gestation using boxplots and two-way repeated measures ANOVA. For participants with visit 5 EFW (n = 1101), predictive accuracy of each individual measurement and their averages was compared with birthweight using average percent error and proportion within 10% of birthweight. One-way ANOVA and chi-square tests were applied. Sensitivity analyses included second-to-last visit, subgroups classified as small- or large-for-gestational age, and a subgroup of participants who delivered within 3 days of visit 5.

RESULTS

Across visits, replicate HC, AC, and FL showed minimal variability, with no significant differences among replicates or across gestation. At visit 5, average EFW and standard deviations were similar across individual and averaged measurements. Percent errors ranged from 8.2 to 8.5% (p = .999), and proportion within 10% of birthweight ranged from 64.4 to 66.4% (p = .954). Sensitivity analyses produced similarly null findings.

CONCLUSIONS

In a controlled research setting with credentialed sonographers and standardized protocols, averaging replicate fetal biometric measurements did not improve EFW prediction of birthweight. A single high-quality measurement of fetal biometry may be sufficient, although further research is warranted to confirm generalizability to routine clinical practice.