Double decidual sac sign
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The double decidual sac sign (DDSS) is a useful feature on early pregnancy ultrasound to confirm an early intrauterine pregnancy (IUP) when the yolk sac or embryo is still not visualized. It consists of the decidua parietalis (lining the uterine cavity) and decidua capsularis (lining the gestational sac) and is seen as two concentric rings surrounding an anechoic gestational sac. Where the two adhere is the decidua basalis, and is the site of future placental formation.
If a double decidual sac sign is present (~53% of IUPs) 6, then it is highly suggestive that the intrauterine fluid collection is an intrauterine pregnancy 7. It is absent in many IUPs, however, and its absence does not define a pseudogestational sac 5.
Should a definite IUP not be confirmed on sonography then repeat scanning and serial quantitative beta-HCGs are required, until either an IUP is established, an ectopic pregnancy is visualized, or beta-HCGs returns to zero (implying miscarriage).
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