title: Unusual Twinning Resulting in Chimerism: A Systematic Review on Monochorionic Dizygotic Twins.
abstract: Traditionally, it is understood that dizygotic (DZ) twins always have a dichorionic placenta. However, with 8% blood chimerism in DZ twins, placental sharing is probably more common than previously has been recognized. In this article, we will review all available cases of monochorionic dizygotic (MCDZ) twins. A total of 31 twins have been described in literature. A monochorionic diamniotic placenta is reported in all cases. Assisted reproductive technology is responsible for the origin of the pregnancy in 82.1% of the cases. In 15.4% of the sex-discordant twins, a genital anomaly was reported in one of the twins. Chimerism is demonstrable in 90.3% of the twins, leading to various diagnostic difficulties. As this review shows that most MCDZ twins are discovered by accident, it can be argued that it is far more common than has been assumed until now. However, the prevalence is still unclear. Awareness of MCDZ twinning is important, with subsequently correct medical strategies. Similarly, the resulting (blood) chimerism is essential to consider in diagnostic procedures, pre- and postnatally. More research on the effect of placental transfusion between sex-discordant twins is required.
authors.affiliation: Department of Obstetrics and Gynecology,VU University Medical Center,Amsterdam,the Netherlands.
authors.forename: Henrike E
authors.initials: HE
authors.lastname: Peters
authors.affiliation: Department of Obstetrics and Gynecology,VU University Medical Center,Amsterdam,the Netherlands.
authors.forename: Tamar E
authors.initials: TE
authors.lastname: König
authors.affiliation: Department of Obstetrics and Gynecology,VU University Medical Center,Amsterdam,the Netherlands.
authors.forename: Marieke O
authors.initials: MO
authors.lastname: Verhoeven
authors.affiliation: Department of Obstetrics and Gynecology,VU University Medical Center,Amsterdam,the Netherlands.
authors.forename: Roel
authors.initials: R
authors.lastname: Schats
authors.affiliation: Department of Obstetrics and Gynecology,VU University Medical Center,Amsterdam,the Netherlands.
authors.forename: Velja
authors.initials: V
authors.lastname: Mijatovic
authors.affiliation: Medical Library,VU University,Amsterdam,the Netherlands.
authors.forename: Johannes C F
authors.initials: JC
authors.lastname: Ket
authors.affiliation: Department of Obstetrics and Gynecology,VU University Medical Center,Amsterdam,the Netherlands.
authors.forename: Cornelis B
authors.initials: CB
authors.lastname: Lambalk
mesh_terms: D046528:Chimerism; D002823:Chorion / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010920:Placenta / Q000502:physiology; D011247:Pregnancy; D059285:Pregnancy, Twin; D027724:Reproductive Techniques, Assisted; D014429:Twins, Dizygotic / Q000235:genetics*; D016216:Ultrasonography, Prenatal
keywords: assisted reproductive technology; chimerism; dizygotic twins; monochorionic placenta; prenatal testing