gestational sac
The earliest ultrasound sign of pregnancy, appearing as a fluid-filled structure within the uterine cavity.
Full Definition
The gestational sac is the first visible sign of pregnancy on transvaginal ultrasound, typically appearing around 5 weeks of gestation as a small, round, fluid-filled structure within the endometrium. It represents the chorionic cavity surrounded by the developing placental tissue (trophoblast). The gestational sac grows approximately 1mm per day in early pregnancy, and its size and growth rate are important parameters for assessing pregnancy viability. A gestational sac without a visible embryo or yolk sac after 8 weeks gestational age may indicate a missed abortion or anembryonic pregnancy. Mean sac diameter measurements are used in conjunction with other parameters to date early pregnancies and assess appropriate development.
Usage
Usage note: Distinguish from pseudogestational sac seen in ectopic pregnancy and from the yolk sac structure within it.
In Context
- "Transvaginal ultrasound revealed a 15mm gestational sac with a visible yolk sac at 6 weeks gestation." — Ultrasound report
- "The gestational sac measured smaller than expected for the given gestational age, raising concerns about viability." — Early pregnancy assessment