On the origin of zygosity and chorionicity in twinning: evidence from human in vitro fertilization

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 form...

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Bibliographic Details
Published in:Journal of assisted reproduction and genetics 2021-11, Vol.38 (11), p.2809-2816
Main Authors: Dirican, Enver Kerem, Olgan, Safak
Format: Article
Language:English
Subjects:
Chorion - growth & development
Female
Fertilization in Vitro - methods
Gynecology
Human Genetics
Humans
In vitro fertilization
Medicine
Medicine & Public Health
Pregnancy
Reproductive Medicine
Review
Splitting
Twinning, Dizygotic
Twinning, Monozygotic
Zygosity
Zygote - growth & development
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Summary: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.
ISSN:1058-0468
1573-7330
DOI:10.1007/s10815-021-02294-y