Tuesday, February 20, 2007

Identical twins
Identical twins occur when a single egg is fertilized to form one zygote which then divides into two separate embryos. This is not considered to be a hereditary trait, but rather an anomaly that occurs in birthing at a rate of about 1:150 births worldwide, regardless of ethnic background. The two embryos develop into fetuses sharing the same womb. When one egg is fertilized by one sperm cell, and then divides and separates, two identical cells will result. Depending on the stage at which the zygote divides, identical twins may share the same amnion, which can cause complications in pregnancy.

For example, the umbilical cords of monoamniotic twins can become entangled, reducing or interrupting the blood supply to the developing fetus. About 50% of mono-mono twins die from umbilical cord entanglement. Monochorionic twins, sharing one placenta, usually also share the placental blood supply. These twins may develop such that blood passes disproportionately from one twin to the other through connecting blood vessels within their shared placenta, leading to twin-to-twin transfusion syndrome.

2 comments:

slw said...

I read your blog with interest as I am pregnant with mono-mono twins. Your statistics are about 15 years outdated, as studies show that with careful in patient monitoring survival rates of these twins has been between 88-100% ( not counting twins with defects NOT relating solely to their mono-mono status) . I suggest you re- re-research, as I am very glad I did not stumble upon thse comments before I knew the true facts!

slw

www.slwmammamia.blogspot.com

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