••• Chapter 16^ First Trimester Ultrasound^173
❍ Is this a normal or abnormal finding?
Normal.
❍ What abnormality could it be mistaken for?
Abdominal wall defects, such as omphalocele and gastroschisis (which should not be diagnosed until the second
trimester).
❍ The midgut typically returns to the abdomen at what week gestation?
11 to 12 weeks.
❍ When can the midgut be seen?
Seen from 8 to 11 weeks with herniation of the fetal bowel into the base of the umbilical cord and 90-degree
counter-clockwise rotation of the bowel around the base of the superior mesenteric artery.
❍ What is the arrow in this first trimester ultrasound pointing to?
The developing rhombencephalon.❍ Is this a normal or abnormal finding?
Normal.
❍ What abnormality could it be mistaken for?
Dandy-Walker malformation or hydrocephalus (which should not be diagnosed until the second trimester).
❍ When can it be seen?
Seen from 7 to 9 weeks, it will eventually contribute to the fourth ventricle, brain stem, and cerebellum.