Early development of the abdominal wall, stomach and heart from 7 to 12 weeks of gestation: a longitudinal ultrasound study.

The purpose of this ultrasound study was to describe longitudinally the normal embryonic development in vivo. Twenty-nine healthy pregnant women were examined five times each with transvaginal ultrasound between 7 and 12 weeks of gestation measured from the last menstrual period. Structures such as the midgut herniation into the umbilical cord, the stomach and the heart were recognized and measured. It was possible to identify the physiological midgut herniation during weeks 7-8. It was always present from 8.5 to 10.5 weeks. At 12 completed weeks, the gut was retracted into the abdominal cavity for all the fetuses. We visualized the stomach in nine embryos (31%) during week 8, in 22 embryos (76%) before 10 weeks, and in all fetuses before 11 weeks. The heart rate increased rapidly to a mean of 175 beats per minute (bpm) at the beginning of week 9. Thereafter it decreased slowly to a mean of 166 bpm at 12 weeks. The mean heart diameter was 22% of the crown-rump length at 7 weeks, 17% at 9 weeks and only 13% at 12 weeks.