Bowel migration in the normal fetus: US detection.

Ten fetuses underwent ultrasound scanning at 7-10 weeks gestational (postmenstrual) age. In all cases, an echogenic mass measuring 0.5-1.0 cm was demonstrated within the base of the umbilical cord at its insertion into the fetal abdomen. No area with echogenicity characteristic of the small bowel was identified within the lower part of the fetal abdomen. All fetuses were reexamined 4-12 weeks later, at which time the mass in the umbilical cord was no longer seen, and normal fetal bowel was visualized in the lower abdominal cavity of the fetus. This sequence of findings appears to represent the sonographic demonstration of normal fetal bowel migration early in gestation and should not be confused with defects of the abdominal wall such as omphalocele or gastroschisis.