Abstract
Vanishing twin syndrome (VTS) refers to the spontaneous reduction of a fetus during multiple pregnancies, resulting in its invisibility during gestation. Vanishing twin syndrome is commonly identified through ultrasonographic examination in early pregnancy; nonetheless, the genetic causes of VTS are rarely detected. This report aimed to investigate the feasibility of genetic testing for VTS using low-coverage whole-genome sequencing and short tandem repeat (STR) analysis. We report a 39-year-old woman who underwent in vitro fertilization and conceived dichorionic diamniotic twins. The heartbeat of 1 fetus ceased at 11 weeks, leading to a diagnosis of VTS, whereas the surviving fetus developed normally and was delivered at full term. Placental examination revealed a rudimentary gestational sac adjacent to the placenta that correlated with the vanished fetus. Chorionic tissues were collected from the placenta of the live-born infant and the rudimentary gestational sac that was considered to have originated from the vanished fetus. Genetic testing of chorionic tissues from the gestational sac and placenta showed that both fetuses were monozygotic twins with a normal 46, XY male karyotype. However, a triallelic pattern at the Penta E locus was identified in the vanished fetus on STR analysis, which was a unique genetic characteristic. This report highlights the feasibility of genetic testing for VTS, despite the unclear relationship between the identified genetic pattern and the vanished fetus.