First trimester fetal biparietal diameter and head circumference in Chinese population

Objectives: To establish the reference ranges for fetal biparietal diameter and head circumference obtained by transabdominal ultrasound examination in the first trimester in Chinese women. Methods: In this prospective cross-sectional study, 1351 normal singleton fetuses were examined transabdominally by 2 experienced observers in the first trimester of pregnancy in which the CRL was between 55 and 84 mm. Measurements of Biparietal Diameter (BPD), head circumference (HC) were prospectively collected. Charts and predictive equations were constructed from data obtained. Results: Measurements of BPD, HC were correlated with CRL. CRL-based predictive equations were calculated using polynomial least squares regression analysis. HC = 7.710583 1.387393 * CRL-0.0037807 * CRL², R² = 0.5735, P = 0.000. BPD = 6.855277 0.2389065 * CRL, R² = 0.5355, P = 0.000. CRL-specific biometric charts were constructed. Conclusions: There was a general increase in fetal biparietal diameter and head circumference with CRL. Chinese fetal biometry might be of help in first-trimester ultrasound examination in the local population.