Intradecidual sac sign

Last revised by Dr Jeremy Jones on 20 Sep 2021

Intradecidual sac sign (IDSS) is a useful feature in identifying an early intrauterine pregnancy (IUP) as early as 25 days of gestation1. The threshold level (earliest one can see the sign) is 24 days of gestation and the discriminatory level (one should always see the sac) is 47 days. As per this sign, site of implantation is seen as an early gestational sac or an intrauterine fluid collection or an echogenic area in a markedly thickened decidua on one side of the uterine cavity. This can be better identified by identifying the collapsed uterine cavity.

Although useful if seen, its presence has been reported in fewer cases of IUP than originally thought (~60%), and its absence does not exclude an IUP.

History and etymology

It was first described by Yeh et al. in 1986.

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Cases and figures

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