title: Twin study: relationship between birth weight, zygosity, placentation, and pathologic placental changes.
abstract: We examined the placentas of 182 like-sexed live-born twins: 73 placentas (40.1%) were monochorionic and 109 (59.9%) were dichorionic. All twin pairs with monochorionic placentas were monozygotic (MZ), but 28.9% of pairs with dichorionic placentas were MZ. Analysis of birth weights demonstrated that dichorionic and dizygotic (DZ) twins were heaviest, and suggested that the chorion status is a more important determinant of birth weight than zygosity. Vascular anastomoses were identified only in monochorionic placentas and occurred in 79.5% of cases. All placentas with deep anastomoses had superficial anastomoses. A higher proportion of velamentous and marginal insertions of the umbilical cord in monochorionic placentas (27.4%) compared to dichorionic placentas (13.8%) supports the belief that lateral placental growth is greatest in twin gestations in which the embryos are initially most closely apposed--The theory of trophotropism.
authors.affiliation: Department of Medical Genetics, Indiana University School of Medicine, Indianapolis.
authors.forename: M A
authors.initials: MA
authors.lastname: Ramos-Arroyo
authors.forename: T M
authors.initials: TM
authors.lastname: Ulbright
authors.forename: P L
authors.initials: PL
authors.lastname: Yu
authors.forename: J C
authors.initials: JC
authors.lastname: Christian
mesh_terms: D001724:Birth Weight; D002823:Chorion; D005260:Female; D005819:Genetic Markers; D006801:Humans; D007231:Infant, Newborn; D010922:Placenta Diseases / Q000150:complications; D010929:Placentation; D011247:Pregnancy; D014427:Twins; D015053:Zygote
chemical_list: D005819:Genetic Markers