In-utero development of the fetal anal sphincter.

Objective To investigate the in-utero development of the fetal anal sphincter using transabdominal ultrasound. Methods This was a cross-sectional study in which the diameter of the fetal anal sphincter was measured sonographically once in 631 well-dated, non-anomalous fetuses scanned between 19 and 38 weeks of gestation. Visualization rates were determined. Regression analysis was used to assess the relationship between the diameter of the fetal anal sphincter and gestational age (GA), and reference values including the mean and 95% reference interval were calculated for each GA. Results The sonographic visualization rate of the fetal anal sphincter increased with gestational age, plateauing at 90-100% between 23-34 weeks of gestation. There was a significant positive relationship between fetal anal sphincter diameter and GA, which was best described by the equation: anal sphincter diameter (mm) = 0.014 x GA(2) + 1.107 x GA - 11.664 (R-2 = 0.62). Conclusion We have provided reference values for the inutero development of the fetal anal sphincter throughout gestation. Copyright (C) 2010 ISUOG. Published by John Wiley & Sons, Ltd.