Fetal abdominal protuberance ratio throughout pregnancy.

We defined "fetal abdominal protuberance ratio" as the ratio between the abdominal circumference (AC) and the distance between the anterior border of the fetal aorta and the posterior surface of the fetal skin (AO-P) and measured it in a total of 358 fetuses between 13 and 40 weeks. The AC and AO-P diameters both grew with gestational age but the increment was steeper for the AC which means a higher protuberance ratio with advancing gestational age.