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Risk of Birth Defects

Hanging cacti lining the Lotusland property. The scientist in me thought they looked like chromosomes.

Ganna Walska Lotusland

Continuing from my last post, let’s talk about my blastocyst worries and congenital anomalies.

Congenital anomaly is medical jargon for birth defects. I separate “birth defects” into 2 different categories: genetics and anatomy.

For now, we’ll touch on the

I will stay very superficial here – we don’t need to get into the science behind it all. Genetic anomalies are problems with the chromosomes. Some genetic anomalies are caused by an extra chromosome. Most people have 2 copies of each chromosome. In some cases, like Down Syndrome, the fetus has 3 copies of a specific chromosome. Down Syndrome has 3 copies of chromosome #21, so it’s medical name is Trisomy 21.

I use Down Syndrome as an example because it is the most common chromosomal defect. The chance  of having a pregnancy with Down Syndrome is directly related to your age at conception: the older your ladyparts, the higher the chance:

  • A 25 year old has a 0.1%  chance.
  • A 35 year old has a 0.4% chance.
  • A 45 year old has a 5% chance.

When I’m asked my age I defer the answer to “a woman never tells her age”. What I really mean is that the statement / question: “you look too young to be a doctor. How old are you?” is both complimentary and completely offensive. I believe questions like that are best left unanswered.

But, for the purposes of my blastocyst, I will tell you that my baseline chance of having a pregnancy with Down Syndrome was higher than 0.1% but lower than 5%.

I also want to reiterate what I said in my last post about miscarriage and genetic anomalies. Often times genetic anomalies end in miscarriage. If a fetus has Down Syndrome, more than 40% of the time that pregnancy will end in miscarriage. Even though a 25 year old has a 0.1% chance of having a pregnancy with Down Syndrome, the chance that she will give birth to a baby with Down Syndrome is less than that.

What about the other genetic problems?

Some genetic anomalies are caused by a flaw in a chromosome.  These flaws can be either spontaneous or inherited from a parent.

The spontaneous flaws are unpredictable, because, well, they are spontaneous. One example of a spontaneous flaw is a syndrome called DiGeorge. Although you probably haven’t heard of it, it has a prevalence of about 1 in 6000 (which is relatively common, all things considered). More than 90% of pregnancies with DiGeorge Syndrome are the result of a spontaneous flaw in a specific area of chromosome #22.

Inherited genetic problems … well, this is a good reason to know your family’s medical history. If multiple family members have the same medical syndrome, there is a chance that the syndrome is inherited.  BRCA (the breast and ovarian cancer gene) is one example of an inherited syndrome. There are genetic tests that can look for flaws in your chromosomes that you may pass on to your children.

So back to my pregnancy …  I didn’t have family members showing me an inherited syndrome, and it was too early in pregnancy for me to know of any spontaneous flaw. I knew my risk was low because the most common of these, DiGeorge Syndrome, has a prevalence of 1:6000.

So, in terms of genetics, my mind was put at ease. These were still pretty good odds for my developing blastocyst.


Jan 17, 2014

Original post published: 

* Content reviewed annually for accuracy 

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