Impact of replacing Chinese ethnicity-specific fetal biometry charts with the INTERGROWTH-21st standard

Abstract

Objective: To assess the impact of adopting the INTERGROWTH-21st biometry standards in a Chinese population. Design: Retrospective cohort study. Setting: A teaching hospital in Hong Kong. Population: A total of 10 527 Chinese women with a singleton pregnancy having a second- or third-trimester fetal anomaly or growth scan between January 2009 and June 2014. Methods: Z-scores were derived for fetal abdominal circumference (AC), head circumference (HC), and femur length (FL) using the INTERGROWTH-21st and Chinese biometry standards. Pregnancies with aneuploidy, structural or skeletal abnormalities, or that developed pre-eclampsia were excluded. Z-scores were stratified as <2.5th, <5th, <10th, >90th, >95th, or >97.5th percentile. Birthweight centile, adjusted for gestation and gender, was categorised as ≤3rd, 3rd to ≤5th, 5th to ≤10th, and >10th. Pairwise comparison and the McNemar test were performed to assess biometry Z-score differences and concordance between the INTERGROWTH-21st and Chinese standards. Main outcome measures: The sensitivity of both the local and INTERGROWTH-21st AC standards to identify pregnancies that were small-for-gestational-age (SGA) was assessed. Results: INTERGROWTH-21st AC, HC, and FL Z-scores were significantly lower than those obtained using our local reference for AC, HC, and FL (P < 0.0001 for all). The proportion of fetuses with biometry in the <2.5th, <5th, <10th, >90th, >95th, or >97.5th percentiles was statistically significant (P < 0.01 for all). A total of 1224 (15.5%) of the scans at 18–22 weeks of gestation had AC, HC, or FL below the 3rd percentile of the INTERGROWTH-21st standard. Conclusions: Adopting the INTERGROWTH-21st standard would lead to a significant number of fetuses being at risk of misdiagnosis for small fetal size, particularly when using HC and FL measures. Tweetable abstract: INTERGROWTH-21st biometry assessment in Chinese leads to fetuses being at risk of misdiagnosis of small fetal size.