Incorporating sonographic cheek-to-cheek diameter, biparietal diameter and abdominal circumference improves weight estimation in the macrosomic fetus

The objective of this study was to improve the accuracy of sonographic fetal weight estimation in macrosomic (> 4000 g) fetuses by combining the cheek-to-cheek diameter (CCD), an indicator of subcutaneous tissue mass, with the biparietal diameter (BPD) and abdominal circumference (AC) in generating a new weight formula. Three hundred well-dated, uncomplicated singleton pregnancies > 32 weeks' gestational age (GA) were analyzed. Sonographic fetal measurements obtained in every case included BPD, head circumference, AC, femur length and CCD. Sonographic estimation of fetal weight (EFW) was derived by using BPD and AC. Actual birth weights (BW) of fetuses delivered within 7 days of the last sonographic examination and weighing over 1500 g (n = 123) were compared to EFW. A formula was derived by correlating BPD, AC and CCD with BW in these 123 fetuses using multiple regression analysis. A second formula was derived from the data of 39 macrosomic fetuses. The two formulae were then tested for accuracy of prediction of fetal weight in 157 other fetuses delivered within 7 days and grouped by birth weight, 44 of them weighing > 4000 g. The new formula for macrosomic fetuses was: EFW (g) = 1065 + 84.5 BPD (cm) + 41.29 AC (cm + 111.0 CCD (cm). In the macrosomic fetuses, a difference of < 10% between EFW and BW was demonstrated in 72.7% by the BPD-AC formula and 95.5% when incorporating CCD. In this group, the mean percentage error was significantly smaller: 4.14 vs. 7.97% (p = 0.0005) In the regression analysis, the contributions of BPD, AC and CCD to the variance in BW were 5.5%, 16%, and 18.3%, respectively (p = 0.008). In the non-macrosomic fetuses, CCD improved prediction of BW, but the trend did not reach statistical significance. Our results demonstrate that, in the macrosomic fetus, CCD explains more of the variance in BW than other parameters and incorporating it in the sonographic weight estimation greatly improves its accuracy.