title: Twin pregnancies: accuracy of first-trimester abdominal US in predicting chorionicity and amnionicity.
abstract: A first-trimester transabdominal ultrasound (US) study was performed on twin pregnancies to determine the utility of US in predicting chorionicity and amnionicity. Among 85 dichorionic-diamniotic (DC-DA) twin pairs, a thick membrane was present in 78 (92%). Four of the DC-DA cases without a thick membrane had two distinct placental sites, allowing 82 DC-DA pregnancies (96%) to be predicted. Among 16 monochorionic-diamniotic (MC-DA) twin pairs, a thin membrane was present in 14 (88%). None of the four monochorionic-monoamniotic (MC-MA) cases had an identifiable membrane. The lambda sign had no value in this evaluation and was actually misleading, while a thick membrane or the identification of two separate placentas was always predictive of DC-DA twinning. However, a thin membrane, while usually predictive of an MC-DA pregnancy, did not exclude a DC-DA gestation. When no membrane is present, an MC-MA gestation is probable; however, a diamniotic pregnancy may still be present, and further evaluation is suggested.
authors.affiliation: Department of Radiology, Jefferson Medical College, Philadelphia, PA 19107-5091.
authors.forename: A B
authors.initials: AB
authors.lastname: Kurtz
authors.forename: R J
authors.initials: RJ
authors.lastname: Wapner
authors.forename: J
authors.initials: J
authors.lastname: Mata
authors.forename: A
authors.initials: A
authors.lastname: Johnson
authors.forename: P
authors.initials: P
authors.lastname: Morgan
mesh_terms: D000650:Amnion / Q000000981:diagnostic imaging*; D002823:Chorion / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D011237:Predictive Value of Tests; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011272:Pregnancy, Multiple; D014427:Twins; D016216:Ultrasonography, Prenatal