First-Trimester Ultrasound: Early Pregnancy Failure

First-trimester pregnancy failure is defined by ultrasound as a lack of sonographic evidence of current or expected viability. Risk factors for pregnancy failure include: increasing maternal age, increased age at first menses, a low β-hCG or progesterone level, cigarette smoking, vaginal bleeding, and a history of prior pregnancy loss. Imaging clues such as an empty gestational sac ≥25 mm or an embryo ≥7 mm without cardiac activity are reliable signs of pregnancy failure. Less reliable signs include an irregular gestational sac, an abnormal or enlarged yolk sac, an empty amniotic sac, embryonic growth less than 1 mm per day, embryonic heart rate less than 85 beats per minute, a chorionic bump, and a subchorionic hematoma. A small gestational sac compared to the size of the embryo is suspicious for pregnancy failure especially when the size difference of the crown rump length to gestational sac size is less than 5 mm.