What Are Conjoined Twins?
Conjoined twins are a type of monozygotic twins. That is, they originate as a single zygote that splits into two. (A zygote is a fertilized egg.) At some point after conception, as the zygote travels towards the uterus for implantation, the cells divide and combine. And in the case of monozygotic twins, the cells split and form as two blastocysts, resulting in twins. This split can occur within a few days, but in some cases, it is delayed and doesn’t split into twelve days or more. That’s when conjoined twins form, twins that develop in the womb with a physical connection. As the name suggests, they are literally two individuals joined together.
Causes of Monozygotic Twinning
It is not known what causes monozygotic twinning, and likewise, no one is absolutely certain what causes conjoined twinning. Although there are theories to explain how conjoined twins form, there is a great deal of uncertainty about the exact cause. Conjoined twinning can’t be attributed to genetics, the mother’s behavior, trauma, a virus, illness, environmental issues or any other factors known at this time. Since it’s not known what causes the situation that produces conjoined twins, there’s also no known way to prevent it from happening. Monozygotic twinning — and conjoined twinning — remain somewhat of an unexplained mystery.
