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First trimester oligohydramnios

Case contributed by Dr Matt A. Morgan


Asymptomatic patient presented for first trimester dating study.

Patient Data

Age: 25-30 years old
Gender: Female

First ultrasound study

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.


Follow up study 13 days later

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.

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Case information

rID: 50547
Published: 11th Jan 2017
Last edited: 25th Dec 2019
System: Obstetrics
Inclusion in quiz mode: Excluded

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