Vrij lab

Stem cell-based model of human monochorionic twin embryo

How human embryos can develop into identical twins, who share the same DNA, is largely unknown. We know that identical twins arise from a single fertilized egg that splits into two and it is believed that the timing of this division affects whether the twins will share a placenta and an amniotic sac. However, what exactly happens and when was not clear due to the rare incidence of monozygotic twins (around 0.4% of pregnancies) and the impossibility to study this inside the womb.

We have now succeeded in forming embryo-like structures that model the early development of human identical twins using only stem cells. This makes it possible for the first time to closely examine how twin embryos are organized and formed. We found that a key part of this process is the rapid growth of the blastocyst, a hollow, balloon-like structure that forms in the earliest days after fertilization and is made of cells that will later become the placenta. As the blastocyst expands, the inner group of cells from which new life can emerge splits into two separate clusters.

This discovery has been published in Advanced Materials (Dorian Luijkx et al. https://doi.org/10.1002/adma.202313306 )

Increased medical risks in twin pregnancies

Assisted reproduction technologies like IVF can increase the chances of having identical twins, possibly due to interventions such as embryo hatching assistance, or IVF culture medium. These interventions come at a crucial developmental stage, potentially increasing the chances of these identical twins sharing a placenta (around 75% of identical twins share a single placenta, named monochorionic twins). Twin pregnancies pose higher risks than single ones, affecting twins and mothers due to complications like uneven blood flow, growth problems, premature birth or postpartum hemorrhage. Yet, practical challenges essentially limit research into twin development and their potential complications. The stem cell-based models that we developed for monochorionic twin embryo can mimic the process leading to identical monochorionic twins. This finally allows us to study the first steps of identical twins, and potentially identify why complications arise in twin pregnancies.