Biomaterial Database

The "twin peak" sign: reliable evidence of dichorionic twinning. 1992

H J Finberg

Phoenix Perinatal Associates, Arizona 85006.

In twin pregnancies with a single placental zone, the presence of a triangular projection of placental tissue beyond the chorionic surface, extending between the layers of the intertwin membrane, has provided reliable evidence that there are two fused placentas (dichorionic, diamniotic) rather than a single shared placenta (monochorionic, diamniotic). This observation, dubbed the "twin peak" sign, was identified in 15 twin pregnancies, all proven to be dichorionic at birth, and in five triplet pregnancies, all proven to be trichorionic. This finding is produced by proliferating chorionic villi growing into the potential space between the two layers of chorion in the intertwin membrane. The single chorion of a monoplacental twin pregnancy serves as an intact barrier, preventing villi from growing between the two amniotic layers. A decision sequence incorporating the use of the twin peak sign is described for determining the type of twinning that has occurred.

UI	MeSH Term	Description	Entries
D011247	Pregnancy	The status during which female mammals carry their developing young (EMBRYOS or FETUSES) in utero before birth, beginning from FERTILIZATION to BIRTH.	Gestation,Pregnancies
D011272	Pregnancy, Multiple	The condition of carrying two or more FETUSES simultaneously.	Multiple Pregnancy,Multiple Pregnancies,Pregnancies, Multiple
D002823	Chorion	The outermost extra-embryonic membrane surrounding the developing embryo. In REPTILES and BIRDS, it adheres to the shell and allows exchange of gases between the egg and its environment. In MAMMALS, the chorion evolves into the fetal contribution of the PLACENTA.	Chorions
D002824	Chorionic Villi	Threadlike vascular projections of the chorion. Chorionic villi may be free or embedded within the DECIDUA forming the site for exchange of substances between fetal and maternal blood (PLACENTA).	Placental Villi,Labyrinth of the Placenta,Labyrinthine Placenta,Placental Labyrinth Layer,Chorionic Villus,Labyrinth Layer, Placental,Placental Labyrinth Layers,Placental Villus,Villi, Chorionic,Villi, Placental,Villus, Chorionic,Villus, Placental
D005260	Female		Females
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D014310	Triplets	Three individuals derived from three FETUSES that were fertilized at or about the same time, developed in the UTERUS simultaneously, and born to the same mother.	Triplet
D014427	Twins	Two individuals derived from two FETUSES that were fertilized at or about the same time, developed in the UTERUS simultaneously, and born to the same mother. Twins are either monozygotic (TWINS, MONOZYGOTIC) or dizygotic (TWINS, DIZYGOTIC).	Twin
D016216	Ultrasonography, Prenatal	The visualization of tissues during pregnancy through recording of the echoes of ultrasonic waves directed into the body. The procedure may be applied with reference to the mother or the fetus and with reference to organs or the detection of maternal or fetal disease.	Fetal Ultrasonography,Prenatal Diagnosis, Ultrasonic,Ultrasonography, Fetal,Diagnosis, Prenatal Ultrasonic,Diagnosis, Ultrasonic Prenatal,Prenatal Ultrasonic Diagnosis,Prenatal Ultrasonography,Ultrasonic Diagnosis, Prenatal,Ultrasonic Prenatal Diagnosis,Diagnoses, Prenatal Ultrasonic,Diagnoses, Ultrasonic Prenatal,Prenatal Diagnoses, Ultrasonic,Prenatal Ultrasonic Diagnoses,Ultrasonic Diagnoses, Prenatal,Ultrasonic Prenatal Diagnoses