Discriminatory ability
The ability of both charts to predict which fetuses would vswould not go on to develop developmentally vulnerability was poor (AUC of 53.0% for INTERGROWTH-21st; 52.8% for WHO; sensitivity of all cut-points < 67% [Tables 4 and 5] ). For example, the 10th centile of the INTERGROWTH-21st had 3% sensitivity and 38% positive predictive value, while the 10th centile of the WHO chart had 6% sensitivity and 36% positive predictive value in identifying developmental vulnerability. It is noteworthy that the 10th percentile of both charts identified considerably less than 10 percent of our cohort as small-for-gestational age: 2.2% of our population was below the 10thpercentile of the INTERGROWTH-21st chart, and 4.9% was below the 10th percentile of the WHO chart. However, discriminatory ability at the percentile of the charts that classified 10 percent of our cohort as small-for-gestational age (the 33rd percentile of the INTERGROWTH chart, the 24th percentile of the WHO chart) was equally poor. The statistically-optimal threshold (i.e., that which maximizes both sensitivity and specificity, based on Youden’s Index) was the 80th percentile of the INTERGROWTH-21st chart, and the 91stpercentile of the WHO chart.