The double decidua sign is a key ultrasound finding indicative of early pregnancy. It is typically seen during the 1st trimester. This sign is characterized by the appearance of two concentric echogenic lines separated by a hypoechoic area, which represents the decidua capsularis and decidua parietalis.
In early pregnancy, particularly in the first trimester (up to 12 weeks of gestation), this sign is a reassuring indicator of an intrauterine pregnancy.
In summary, the double decidua sign is most commonly observed during the first trimester.