Fetal bowel. Normal sonographic findings.

The normal sonographic appearance of fetal colon and small bowel is reported in a prospective study of 130 fetuses. The colon, which appeared as a continuous tubular structure located around the perimeter of the abdominal cavity, was seen in some fetuses as early as 22 menstrual weeks and in all fetuses examined after 28 weeks. Colon diameter demonstrated a linear relation (r = 0.82) with menstrual age, reaching a maximum of 18 mm at term. In comparison, small bowel was located centrally and individual segments never exceeded 7 mm in diameter or 15 mm in length. Small bowel loops were seen in only 30% of fetuses examined after 34 weeks. Peristalsis was routinely demonstrated of the small bowel, but was not observed in the colon.