By: Idries J. Abdur-Rahman, MD, FACOG
Obstetrician/Gynecologist
So what is Trisomy? Well to answer that questions we have to take a quick trip back to high school genetics. All humans have 46 chromosomes arranged in 23 pairs. We get 23 chromosomes from mom and 23 from dad. The word trisomy refers to a condition in which there is a third copy (tri-) of a specific chromosome (-somy). There are many different trisomy’s and the particular syndrome that results depends upon which particular chromosome the affected individual has three copies of. The most commonly known trisomy is trisomy 21 (three copies of the 21st chromosome) much more commonly known as Down’s Syndrome.
So why are we talking about trisomy’s? Well, other than the fact that March is trisomy awareness month, 1 in 100 (1% of) pregnancies will be affected by a trisomy so the condition is not nearly as uncommon as people might think. Many trisomy’s result in early pregnancy loss (miscarriage) but a significant minority do result in live births.
Can trisomy be prevented? In most cases, the short answer is no. Trisomy is a condition that occurs before conception (either the sperm or the egg has an extra chromosome) and there are no current therapies that can reverse or treat the condition once fertilization has occurred. The great majority of pregnancies affected by a trisomy will result in early (usually first trimester) miscarriage but many affected pregnancies do continue to term resulting in a live birth. The only way to prevent trisomy is IVF (in vitro fertilization) and even this does not prevent trisomy. Instead it allows for only genetically health fetuses to be implanted due to pre-implantation genetic testing.
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