Description and genetic analysis of three sets of monozygotic twins resulting from transfers of single embryos to recipient mares.

This research article is about investigating the occurrence and genetic origins of monozygotic twin pregnancies in mares, which unexpectedly resulted from single embryo transfers.

Summary of the study

• The study examined three cases of monozygotic twin pregnancies in recipient mares which all resulted from transfers of single embryos. Monozygotic twins refer to twins who are genetically identical and usually occur when a single fertilized egg splits into two.
• Before day 25 of gestation, only one embryonic vesicle (or gestational sac) was observed in all three mares. This is notable because in twins, typically two embryonic vesicles would be expected.
• However, one mare was found to have two distinct vesicles each containing an embryo on day 37 of gestation. This was revealed via an ultrasonographic examination (an imaging method used to visualize the inside of the body).
• In the other two mares, only one vesicle and embryo were identified on day 30 of gestation. Yet, a more thorough ultrasonographic scan for a second conceptus (or an embryo in the stage of development before differentiation of organs) had not been performed on day 30 – mainly due to the initial observation of only one embryo during early gestation.

Results

• Tragically, all the twin pregnancies led to the death of both the fetuses. The reason for this is not explicitly stated in the abstract.
• Through genetic analysis, it was confirmed that each set of monozygotic twins came from the originally transferred single embryo. This was an important finding as it verified the onset of twin pregnancies from the transfer of just one embryo.

Conclusion and Implications

• The research concluded that monozygotic twin pregnancy can occur after a single embryo transfer into the mother. Therefore, it’s recommended that recipient mares should undergo thorough examination for multiple conceptuses, especially during 25 to 30 days of gestation.
• Bearing in mind that the allantoides (part of the fetal membrane) of monozygotic twins should be seen via an ultrasonographic scan during this period, conducting the scan would enable effective management of the mare’s pregnancy if multiple conceptuses are detected.
• The findings underscore the importance of careful monitoring during gestation, even when just a single embryo transfer has been carried out, to detect unexpected twin pregnancies early and to better manage the health and wellbeing of the mare.