Nomograms of fetal thoracic dimensions from 17 to 37 weeks of gestation

Abstract Introduction: We aimed to construct the nomograms for fetal thoracic parameters among Thai fetuses that were between 17 and 37 gestational weeks, as assessed by three distinct two‐dimensional (2D) measurement techniques (thoracic diameter, circumference and area) and compare our findings with those of previous publications. Methods: A cross-sectional study involving 511 low-risk singleton pregnancies with normal fetuses at Siriraj Hospital, Bangkok, Thailand, was conducted. Using the four-chamber view, fetal thoracic measurements were obtained through three 2D sonographic measurement methods. Reference intervals at 95% and Z -scores were established for all techniques based on gestational age (GA) and biparietal diameter (BPD). Intraclass correlation coefficients (ICCs) were computed to assess reproducibility of the measurement methods. Results: Measurements of fetal thorax size exhibited consistent, proportional increases with advancing GA and BPD across all techniques. Intraobserver and interobserver reliability coefficients for all methods indicated excellent agreement, with all ICCs being at least 0.991. Nomograms of fetal thoracic diameter, circumference and area across GA and BPD were constructed from the obtained values. Discrepancies in Z -score reference ranges for fetal thoracic circumference were noted between the present study and previous research in other populations, particularly among Caucasians. Conclusion: Our study established normal reference ranges for evaluating fetal chest size through three different methods from 17 to 37 weeks of gestation in the Thai population. Nomograms may vary due to population differences, emphasising the importance of using reference values from similar demographic groups. The findings could potentially be used to identify fetuses that are at risk of abnormal thoracic dimensions or thoracic dysplasia.