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.

Twin anemia‐polycythemia sequence with blood chimerism in monochorionic dizygotic opposite‐sex twins

“…More than 50% of MCDZ twins are conceived using fertility treatments (in vitro fertilization, 32.1%; intracytoplasmic sperm injection, 25%; intrauterine insemination, 14.3%; ovulation induction, 10.7%). 3 In recent years, the number of assisted reproductive technology-related pregnancies has been increasing. 4 It is therefore possible that the incidence of MCDZ twins will continue to rise.…”

“…Of note, MCDZ twins are prone to genetic problems. Reportedly, 90.3% of MCDZ twins have blood chimerism, 3 where both twins possess two karyotypes: 46XX and 46XY. This phenomenon may cause problems with blood typing or blood transfusion.…”

Unusual twinning: Additional findings during prenatal diagnosis of twin zygosity by single nucleotide polymorphism (SNP) array

“…In 90.30% of the MCDZ twin pairs, blood chimerism was noticeable. However, among the sex‐discordant MCDZ twins, the incidence of 1 of the twins with a genital anomaly was 15.40%, and this anomaly was mainly caused by blood chimerism . Of the ART twin pairs with MC placentas, if 2 or more embryos were transferred or if blood chimerism or a fetal genital anomaly was evident, we needed to be alerted to the occurrence of MCDZ, and a precise zygosity diagnosis by SNP array was necessary to identify these cases.…”

“…However, among the sex-discordant MCDZ twins, the incidence of 1 of the twins with a genital anomaly was 15.40%, and this anomaly was mainly caused by blood chimerism. 23 Additionally, we also found an artery-to-artery vascular anastomosis in the placental examination of this DCMZ twin pair due to the transfer of 2 day-5 blastocysts. Traditionally, vascular anastomoses in placentas are an important prognostic factor for the outcome of multiple pregnancies, which has been described in cases of MC placentas.…”

The first case of congenital blood chimerism in two of the triplets in Korea

“…Chimeras are defined as individuals with cells are derived from two or more zygotes. While blood chimerism was usually an issue of detecting engraftment in hematopoietic stem cell transplantation, recent advances in artificial fertilization have resulted in increased detection of congenital blood chimerism . Congenital blood chimerism arises from the exchange of hematopoietic cells through communicating blood vessels between multiple births .…”