Gestational Sac
The earliest ultrasound sign of pregnancy, appearing as a fluid-filled structure within the uterine cavity.
Full Definition
The gestational sac represents the first sonographic evidence of pregnancy, typically visible by transvaginal ultrasound at 4.5-5 weeks gestation when beta-hCG levels reach 1,000-2,000 mIU/mL. This anechoic (fluid-filled) structure appears within the endometrium and contains the developing embryo and associated structures. In ART cycles, gestational sac identification confirms intrauterine pregnancy location and successful implantation. The sac demonstrates progressive growth, and assessment includes measurement, location verification, and evaluation for embryonic structures. Absence of a gestational sac despite appropriate hCG levels may suggest ectopic pregnancy or pregnancy of unknown location, requiring further investigation and monitoring.
Usage
Usage note: Hyphenate when used as compound adjective; maintain as two words when used as noun.
In Context
- "Transvaginal ultrasound confirmed intrauterine gestational sac measuring 8mm at 5 weeks 2 days gestation." — Ultrasound report
- "The absence of gestational sac despite beta-hCG of 1,800 raised concern for ectopic pregnancy." — Clinical assessment documentation