Decidual reaction

Last revised by Joshua Yap on 12 Aug 2022

A decidual reaction is a feature seen in very early pregnancy where there is thickening of the endometrium around the gestational sac, which is seen as an echogenic rim on ultrasound. A thin decidual reaction of <2 mm is considered one of the features suggestive of an anembryonic pregnancy 2. A decidual reaction in some situations can also occur in an ectopic pregnancy 3.

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