FIRST TRIMESTER PREGNANCY FAILURE - THE
ENLARGED AMNIOTIC CAVITY |
The amniotic cavity with its surrounding membrane lies within the chorionic cavity. Although both these cavities grow, the
amniotic cavity grows faster than the chorionic cavity.
At 16-17 weeks they eventually fuse to become the chorio-amniotic
membrane.
NORMAL GESTATIONS |
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Small Amniotic
Cavity |
Normal Amniotic Cavity
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Large Amniotic
Cavity |
Fetus too big for amniotic cavity |
Normal relationship
between fetus and amniotic cavity |
Amniotic cavity too big for fetus |
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8 wks – normal amniotic cavity and fluid |
8 wks – enlarged amniotic cavity due to large
amount of amniotic fluid. |
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- Amniotic and chorionic cavities grow proportionally.
- <6.5 weeks GA the amnion is so close to the embryo that it is not usually seen (CRL = diameter of amniotic cavity) (1).
ABNORMAL GESTATIONS |
- Relationship (1).
- Amniotic cavity is too large for the embryo (1).
- Amniotic cavity diameter > CRL of embryo.
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Normal embryo and amniotic cavity |
Amniotic cavity too large for embryo (8
wks) |
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Scan
at 11 wks 4 days demonstrates that the embryo demised at 8 wks 2 days |
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Another case Note
the large enlongated gestational sac and the
abnormal relationship between the amnion and amniotic cavity at 8 wks 3 days |
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REFERENCES |
- Horrow MM. Enlarged amniotic cavity: A new sonographic sign of early embryonic death. AJR 1992;158:359-362.