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

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 >975th 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-21' and Chinese standards. Main outcome measures The sensitivity of both the local and INTERGROWTH-214 AC standards to identify pregnancies that were small-for-gestational-age (SGA) was assessed. Results INT ERGROWTH-21 't 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 Fi. below the 3rd percentile of the INTERGROWTH-21' standard. Conclusions Adopting the INTERGROWEH-21' 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.