Intrauterine Membranes Unassociated with Amniotic Band Syndrome
· Amnion- Visualization of the amnion in the first trimester of pregnancy is of no clinical significance and is unassociated with anomalies recorded with ABS.
· Normal chorioamniotic separation- Separation of the amniotic from the chorionic membrane is normal in early pregnancy until fusion of the two membranes at approximately 16 weeks.
· Traumatic chorioamniotic separation- This may follow amniocentesis; the process is benign and usually has no associated abnormalities.
· Extrachrionic separation- Extrachorionic hemorrhage separates the chorioamniotic membrane from the uterine wall, allowing visualization.
· Diamniotic twin- In diamniotic twin the separating membrane is a well shown sonographic finding.
· Septate uterus- Septate uterus is a congenital abnormality; the septum is usually fundal.
· Asherman's syndrome- Intrauterine synechiae (complete or incomplete) may follow cesarean section, myomectomy, trauma, inflammation, curettage, manual removal of the placenta, septic abortion, endometriosis, etc. Over 70% have usually had instrumentation of the endometrial cavity. The sheets seen on ultrasound consist of two layers of amnion and chorion around the scar. Fetal entrapment does not occur. Patients usually have a low pregnancy rate.
· Amniotic sheets/shelves- These have a thickened base with a free edge protruding into the amniotic cavity. They are not fixed to the fetus. The fetus can move freely around the membrane and does not become deformed.
· Intra-amniotic membrane following amniocentesis-
Real time sonography demonstrates active bleeding if the needle penetrates the placenta/chorionic plate vessels following amniocentesis. Bleeding is visible on real time sonography as bright flakes which float in the amniotic fluid, settling in the most dependent area of the sac. Blood may clot in strings/bands stretching from the placenta to the fetus.
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