Ultrasonographic measurement of the yolk sac.

Ultrasonographic measurements of the yolk sac were made during first trimester in 100 pregnancies. The results were related to the crown-rump length of the embryos and showed an increase in size from 7 to 11 weeks menstrual age. A possible relation between anomalies in yolk sac development and embryonic development was studied in six patients by means of serial weekly ultrasonographic examinations. In one case with absence of the yolk sac embryonic death occurred at 10 weeks menstrual age; the embryo had spina bifida.