Open AccessOn the origin of zygosity and chorionicity in twinning: evidence from human in vitro fertilization
Author(s) -
Enver Kerem Dırıcan,
Şafak Olgan
Publication year - 2021
Publication title -
journal of assisted reproduction and genetics
Language(s) - English
Resource type - Journals
eISSN - 1573-7330
pISSN - 1058-0468
DOI - 10.1007/s10815-021-02294-y
Subject(s) - zygosity , in vitro fertilisation , blastocyst , reproductive medicine , gestation , obstetrics , single embryo transfer , embryo , embryo transfer , monozygotic twin , gynecology , oocyte , biology , human fertilization , human genetics , andrology , zygote , pregnancy , medicine , genetics , embryogenesis , gene
Assisted reproduction is presumed to increase monozygotic twin rates, with the possible contribution of laboratory and medical interventions. Monozygotic dichorionic gestations are supposed to originate from the splitting of an embryo during the first four days of development, before blastocyst formation. Single embryo transfers could result in dichorionic pregnancies, currently explained by embryo splitting as described in the worldwide used medical textbooks, or concomitant conception. However, such splitting has never been observed in human in vitro fertilization, and downregulated frozen cycles could also produce multiple gestations. Several models of the possible origins of dichorionicity have been suggested. However, some possible underlying mechanisms observed from assisted reproduction seem to have been overlooked. In this review, we aimed to document the current knowledge, criticize the accepted dogma, and propose new insights into the origin of zygosity and chorionicity.