Increasing curvature of the normal fetal ductus arteriosus with advancing gestational age.

In order to determine whether the configuration of the normal fetal ductus arteriosus changes with increasing gestational age, we prospectively collected oblique transverse sonographic images of the fetal thorax through the ductus arteriosus. Scans from 240 consecutive normal fetuses with gestational age 20 weeks or more were included in the study. The images were reviewed independently by two sonologists and the ductus arteriosus was graded as: (1) straight; (2) mildly curved (C-shaped, bending < 90 degrees from a straight line); or (3) markedly curved (C-shaped, bending > 90 degrees, or S-shaped). In cases where the two sonologists' gradings did not concur, the images were re-reviewed jointly by both sonologists and a grading was assigned by consensus. Forty-two cases were rejected, due to inadequate images. The ductus arteriosus was graded in 42 fetuses aged 20-25.9 weeks, 48 at 26-31.9 weeks, 74 at 32-37.9 weeks, and 34 at 38 weeks or more for a total of 198 cases. There was a significant trend to greater curvature with increasing gestational age (p < 0.0001). The frequency of a straight ductus arteriosus decreased steadily from 55% of fetuses aged 20-25.9 weeks to 3% of fetuses at 38 weeks or older, while the frequency of marked curvature increased from 2% in the youngest age group to 56% in the oldest. The proportion with mild curvature showed little variation throughout gestation. In summary, the configuration of the ductus arteriosus is variable but tends to become more curved as pregnancy proceeds. Marked curvature or tortuosity of the ductus arteriosus should not be misinterpreted as a great vessel anomaly.