Objectives: To determine intra- and inter-observer reproducibility of the ultrasound measurement of pelvic inlet in the first trimester of pregnancy. Methods: Transabdominal pelvic ultrasound was performed to measure the pelvic inlet anteroposterior diameter using a 2D probe in twelve Chinese women having a singleton pregnancy. Scans were performed in the first trimester by three sonographers. The pelvic inlet anteroposterior diameter was defined as the distance between the anterior surfaces of the sacral promontory and the superior medial border of the pubic bone most adjacent to the pubic symphysis. Intra-observer repeatability was determined and analysis of variance was performed to assess inter-observer measurements. The bias between any two sonographers’ measurements was assessed by calculating the 95% confidence interval for the mean difference between sonographers paired measurements. Results: Intra-observer reproducibility was 0.71 cm. Analysis of variance indicated that there was no significant difference between sonographers’ measurements (p = 0.46). The bias between two sonographers’ measurements ranged from 0.05 to 0.32 cm. Conclusion: It is technically feasible to measure the pelvic inlet diameter using ultrasound (USG) at the first trimester. High inter-observer reproducibility can be achieved. Further studies are required to establish the potential role of this technique and the measurement of the pelvic inlet diameter in prediction of labor outcome.
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