genetic screening

Genetic Screening for Birth Defects

Couples who are getting started with fertility therapy have options that most couples trying to conceive (TTC) don’t even consider right off the bat. One of these options is genetic screening for birth defects. Also called “carrier screening” or “pre-conception genetic screening,” the information you learn from these tests can assess the risk of giving birth to a baby with birth defects – and will assist you and your fertility specialist in selecting the best plan for moving forward.

While some birth defects occur after a baby is conceived, and have nothing to do with the parents’ genetics, others are already “living” in you or your partner’s DNA, unexpressed in your bodies but with the potential to express in your child’s.  The majority of these are called autosomal recessive defects. If both you and your partner are carriers for the same autosomal recessive defect, there is a 25% chance (1 in 4) that your baby will be born with that particular disorder.

Currently, about 5% of all pregnancies in the United States result in a baby with a birth defect. These defects range from cleft lips or enlarged hearts, to cystic fibrosis and sickle cell anemia. While we don’t (yet) have a way to test for all of them, we can prevent some of the more common and/or severe ones. This is the ultimate goal of genetic carrier screening.

Pre-Conception Genetic Screening Helps Parents Make Better Choices

We recommend opening up the conversation about pre-conception genetic screening at the first consultation with your fertility specialist. Here at NCFMC, we recommend that women are screened first, because some birth defects are linked to the X chromosome, meaning women can be silent carriers for genetic problems than men.

If it turns out the woman is not a carrier for any disorders, there’s probably no reason to test the male partner since the chances of having a child with a genetic birth defect go way down in that case, and we continue to move along the fertility treatment pathway. If, however, the male partner has a family history of a genetic disorder, that is a different story because your children could be potential carriers.

If genetic screening determines that the woman is a carrier for a specific genetic birth defect, we absolutely want to test the male as well. If both partners test positive for the same genetic disease then, for autosomal recessive disorders, there is a 25% chance the child will have a serious birth defect. In order to prevent a serious birth defect, we can perform a test on all of the embryos before any are implanted into the uterus, that is, before pregnancy even occurs. This testing is called Preimplantation Genetic Testing (PGT) and requires in vitro fertilization (IVF).

IVF with PGT is a very powerful tool and has prevented innumerable birth defects. In the past, most couples only tragically discover that they are both carriers for the same genetic birth defect after they have an affected child. Also in the past, the only tools to determine if a future child would have a serious birth defect would be to test the fetus when the women was 3 – 4 months pregnant and then make the difficult decision to abort the pregnancy, or not. Conversely, PGT allows testing an embryo for a serious birth defect before the woman is even pregnant.

Screening For Specific Birth Defects

Pre-conception genetic screening is a simple blood test. Currently we can test for about 300 different birth defects – although many of them are incredibly rare.

In most cases, your health history, ethnicity and family medical history will guide which defects we look for. The four most common birth defects we screen for are:

  1. Cystic Fibrosis (CF). This is the most common disorder affecting Caucasians. Roughly 4% of the Caucasian race are carriers. It is a terrible lung disease. Patients with CF spend a large amount of their time in doctor’s offices and hospitals, and have a life expectancy of about 30 years. To screen for this, the lab looks for DNA mutations in the CFTR gene. We should note that some men have extremely mild forms of CF that has gone completely undetected. However, one of the side effects can be a lack of vas deferens, which prevents the sperm from being able leave the penis. So, carrier screening for CF may result in important infertility diagnosis information as well. CF testing has been incorporated into all carrier screening blood panels, but the number of CF mutations that are tested for can vary.
  2. Sickle Cell Anemia. This is the most common disorder in the African-American population. About 10% of the African American population are carriers. If both parents are carriers then there is a 25% chance of having a child with serious sickle cell anemia. Many patients with sickle cell spend their lives in severe pain and die at a young age. Lab technicians use a blood test and then a process called electrophoresis, which identifies whether or not you are a carrier. Testing for sickle cell anemia and sickle trait have been incorporated into genetic carrier screening panels to some extent.
  3. Thalassemia. There are multiple types of thalassemia, which causes mild to severe anemia. This is a common gene mutation in those of Mediterranean or Southeast Asian descent. For this screening, lab techs run a complete blood count (CBC) panel and analyze the mean corpuscular volume (MCV). If the MCV is low, an electrophoresis should be performed to see if thalassemia is the cause. Testing for most kinds of thalessemia has been incorporated into most genetic carrier screening panels.
  4. Spinal Muscular Atrophy. This genetic disorder manifests in mild and severe forms. In most cases, babies with spinal muscular atrophy die within the first five-years of life. This condition is not ethnicity-specific. Once your blood is drawn, it will be evaluated, and techs will look for disorders in the SMA genes. SMA testing has been incorporated into all genetic carrier screening panels.
  5. Tay- Sachs Disease. While typically recommended for couples of Jewish descent, French Canadians and Cajuns also have higher risks of giving birth to babies with Tay-Sachs. It is devastating disease resulting in death by age 5 years. About 1 in 30 Ashkenazi Jews are carriers for Tay Sachs- and the majority of Jews in the U.S. in the U.S. are of Ashkenazi descent. If you are of Jewish descent, we also recommend screening for other autosomal recessive diseases, such as Bloom syndrome, Canavan Disease, Familial Dysautonomia and several others that can be fatal and result in life expectancies of 5-years of less.

Because the United States is an ethnic melting pot of genes, we offer and recommend genetic carrier screening for all of our patients. Most testing can be accomplished by one blood draw that test for all of the above disorders, and often many more disorders, in one comprehensive panel.

Sex-Linked Genetic Disorders

We mentioned sex-linked genetic disorders in our introduction. These disorders are found only on the X-chromosome. Since the female egg carries one X chromosome, women who are carriers for sex-linked defect, also called an X-linked disorder, have a 50/50 chance of passing that disorder on to their sons and their daughters can be carriers.

Two of the most common X-linked birth defects are:

  • Fragile X. After Down Syndrome, this is the most common cause of mental retardation. Women who are carriers of Fragile X experience higher rates of premature menopause. So, again, this information is important for the health of your child as well as your fertility future.
  • Deschene’s Muscular Dystrophy. This is a devastating disease the affects the entirety of the muscular system. Boys with DMD often die before age 10 and if they live, they are typically wheelchair bound and lead extremely debilitated lives.

Before your first consultation with a fertility specialist, begin questioning and having conversations with your immediate and extended families. The more you know about genetic issues (including fatal ones) in aunts, uncles, cousins, grandparents, etc., the more information you’ll be able to bring to your fertility specialist. For example, you may find that one of your grandparents or great grandparents had a baby that didn’t live long, or a toddler that weakened and died – and the symptoms were that of one of the diseases we’ve mentioned here. That can help us decide how important pre-conception screening may be for you and your partner, as well as which conditions we’ll want to screen for.

Also, if one of you – or the both of you – have an existing child with a genetic disorder, you should be screened. Similarly, if your screening reveals genetic disorders – or that you are a carrier – we recommend that your family members are all tested as well to determine whether they are carriers – this includes existing children.

The Cost of Genetic Screening

One of the reasons we feel so good about the prospects of pre-conception genetic screening is that it is such an affordable procedure with such meaningful outcomes. The average patient pays less than $100 for a basic screening, and a more detailed complete screening runs about $350. Since most health insurance policies will cover a portion of the costs, your out-of-pocket expenses may be even less than that.

Those prices are significantly cheaper than the cost for PGT, which runs about $3000 to $5000. If you and your partner have both been screened and cleared, there is a much slimmer chance your child would be born with one of the more common genetic birth defects. It’s important to remember that while these tests yield the most accurate information, we can give you at this point in time, there is never a 100% guarantee.

Any time we detect a couple with an infertility diagnosis that also has a high chance of producing a baby with a serious genetic disease, we recommend skipping all the “beginning” fertility treatments and jumping right to IVF with PGT. That way, we can use PGT to detect which embryos are affected by the disease, which ones are carriers of the disease and which embryos are not even carriers of genetic defects. Then, we only transfer embryos that are not affected with a serious birth defect. This provides couples with the best chances of IVF success – and it decreases the chances of failed implantation, miscarriage or a baby born with a birth defect.

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