gestational sac

arises from blastocyst which implants into secretory endometrium; surrounded by echogenic trophoblast

sac size:

6th week = 17mm;
8th week = 31 mm
fills chorionic cavity by 12th week

visualization of gestational sac

relative to beta-hCG levels:
- transabdominal scan: > 1800 IU/l
- transvaginal scan:
  - < 500 IU/l = 20%
  - 500-1000 IU/l = 80%
  - > 1000 IU/l = 100%
- relative to menstrual age
  - transabdominal scan: earliest by 5.5 weeks (10-12mm)
  - transvaginal scan: routinely seen by 5-5.5 weeks

see: double decidual sac

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© 2002, C.E. Kahn, Jr.
2002-04-18