945 Fetal biometry using hadlock versus INTERGROWTH-21st in an urban zambian population

Abstract

Numerous growth curves and formulas have been developed to calculate estimated fetal weight (EFW) from prenatal ultrasound (US). The four-parameter Hadlock formula (head circumference (HC), biparietal diameter, abdominal circumference (AC), and femur length) remains the most commonly used in the United States. The two-parameter INTERGROWTH-21st formula (HC and AC) was created to provide a more comprehensive international standard using fetal growth data from multiple countries. We sought to evaluate whether EFW calculated by Hadlock or INTERGROWTH-21st at 32 weeks better predicts birthweight (BW) in an urban Zambian population. The Zambian Preterm Birth Prevention Study (ZAPPS) is an ongoing prospective cohort of pregnant women enrolled at a tertiary hospital. We included women with singleton pregnancies who underwent a dating US at < 24 weeks and fetal biometry at 32 weeks. Estimated due date was calculated by US at the enrollment visit for each patient using Hadlock and INTERGROWTH-21st. EFW at 32 weeks was calculated by Hadlock and INTERGROWTH-21st formulas using the corresponding gestational age by each formula respectively. Data were analyzed using chi-square, t-test, and linear regression as appropriate. 1450 women were enrolled in the first phase of ZAPPS from 2015 to 2017. 32-week US (mean 32.1 ± 0.7 weeks) was available for 749 women. The mean EFW was 1895 ± 194g by Hadlock and 1788 ± 203g by INTERGROWTH-21st. Birthweight was available for 708 maternal-infant pairs (49%); mean birthweight was 3056 ± 487g. In an unadjusted linear regression model, EFW at 32 weeks by Hadlock and INTERGROWTH-21st were comparable predictors of birthweight. For both models, p <0.001, and adjusted R2 was 0.11 (Figure 1). A Bland-Altman plot (Figure 2) demonstrates that EFW by Hadlock is on average 107g higher (SD 74, 95% limits of agreement 107 ± 148g). Hadlock and INTERGROWTH-21st formulas are similar predictors of birthweight in an urban Zambian cohort. This suggests that INTERGROWTH-21st offers an acceptable two-parameter alternative to calculate fetal biometry.View Large Image Figure ViewerDownload Hi-res image Download (PPT)