title: Prolapse of the amniotic sac ("hourglass membranes"): ultrasound appearance.
abstract: Prolapse of the amniotic sac through the partially dilated cervical os in pregnancy is called "hourglass membranes." Ultrasonography may be useful in identifying the presenting fetal or intra-uterine parts within the bulging membranes.
mesh_terms: D000328:Adult; D000650:Amnion; D005260:Female; D006801:Humans; D011247:Pregnancy; D011248:Pregnancy Complications / Q000175:diagnosis*; D011391:Prolapse; D014463:Ultrasonography