Supplementary Material for: Third-Trimester Conditional Reference Values for Longitudinal Fetal Growth Assessment

<p><b><i>Objectives:</i></b> The aim of this study was to derive longitudinal reference values of fetal growth (estimated fetal weight [EFW] and abdominal circumference [AC]) during the third trimester and to develop coefficients for conditional growth assessment. <b><i>Patients and Methods:</i></b> A prospective cohort study was conducted involving consecutive singleton pregnancies in a low-risk population for a routine third-trimester scan at 30<sup>+0</sup>-34<sup>+6</sup> weeks and follow-up at 37<sup>+0</sup>-38<sup>+6</sup> weeks for an additional ultrasound. Statistical analysis was based on multilevel modeling using MLwiN software. Unconditional centiles were calculated from z-values at each gestational age, and conditional centiles were calculated from z-values at a given measurement (30-34 weeks) and the expected measurement (37-38 weeks). <b><i>Results:</i></b> At 30-34 weeks, 8 and 9.3% of the fetuses had an unconditional EFW below the 10th and above the 90th centile, respectively. At 37-38 weeks, these figures were 10.3 and 9.3%, respectively. Regarding the unconditional AC, at the first scan, 8.9 and 9.6% had values below the 10th and above the 90th centile, while at the second scan 10.5 and 10.5% had values below the 10th and above the 90th centile, respectively. The proportion with a conditional EFW below the 10th and above the 90th centile was 10.2 and 9.4% at the second scan, respectively. For conditional AC, these figures were 10.7 and 10.3%, respectively. <b><i>Conclusion:</i></b> We have produced reference centiles for EFW and AC growth during the third trimester as a useful tool for quantifying growth.</p>