Twin Zygosity is one thing, but Triplets?
Last week, an article on cnn.com told the story of New York mom Allison Penn and her newborn sons, Logan, Eli and Collin. The boy’s births were already notable because they are triplets— a rare event that only happens in about 1 in every 8,000 births.
Logan, Eli and Collin are not just any triplets, however. They are identical triplets, which means that the three babies grew out of only one fertilized egg. In multiple identical births, one fertilized egg (called an embryo) splits during development, resulting in identical babies, most often, twins. (In contrast, fraternal twins result from two separate eggs being fertilized.)
In the case of the Penn triplets, one of the resulting embryos split again, resulting in three embryos and, ultimately, three babies. This “double splitting” of a fertilized egg, resulting in identical triplets, is extremely rare and occurs only once in every 500,000 births, although some data suggests the chances of identical triplets can even be one in 200 million. Like identical twins, identical triplets have exactly the same DNA because they came from the same fertilized egg.
A DNA test called a Zygosity Test is often used to tell if twins or triplets are identical or fraternal. Through a simple cheek swab after the babies are born, scientists can determine whether or not the babies’ DNA matches—which means the babies are identical—or does not, which means they are fraternal. Twins are either identical or fraternal, while triplets can consist of one set of identical twins and a third fraternal baby, three fraternal babies, or three identical babies, like Logan, Eli and Collin Penn.
What makes Logan, Eli and Collin’s births even more special is that they are a result of in-vitro fertilization (IVF), a fertility treatment that involves harvesting an egg from the mother and fertilizing it with the father’s sperm outside the womb, and then implanting it in the mother’s uterus hoping that the embryo will grow and ultimately result in pregnancy.
The rate of multiple births rises if a couple uses IVF because often multiple embryos are implanted in the mother to increase the chance of achieving a successful pregnancy. However, in Allison Penn’s case, she had only one embryo implanted, making her chance of having identical triplets extremely low.
In fact, doctors believe the Penn babies are the first identical triplets to be born through an IVF procedure that involved implanting only a single embryo. All three babies are healthy, although one boy has a non-functioning kidney but doctors don’t think he will require medical treatment.
This entry was posted
on Friday, March 14th, 2008 at 6:42 pm and is filed under Home Paternity Tests.
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