Presentation
Asymptomatic patient presented for first trimester dating study.
Patient Data
On this first trimester ultrasound study, the 7 week 3 days embryo appears normal, but the amount of fluid in the gestational sac appears low. The mean sac diameter is 14 mm. The embryo crown rump length is 12 mm.
On this study 13 days later, the embryo has increased in size a little, but the contour is less well defined and there is no longer a heart rate.
Case Discussion
On the first study, the difference between the mean sac diameter (14 mm) and the embryo crown rump length (12 mm) is less than 5 mm. Since the difference is less than 5 mm, this is considered "first trimester oligohydramnios" and is suspicious for a failed early pregnancy (although not definite).
On the follow up study 13 days later, there is no longer a heartbeat in the embryo. The early pregnancy has failed.