Genetic Testing During Pregnancy


(instrumental music) Our genetics are determined by the chromosomes in our cells. You have the option to screen for a number of genetic
disorders in pregnancy. Some examples are down syndrome, turner syndrome, and
chromosomal trisomies. Genetic disorders occur if the fetus does not have the usual
number of chromosomes or if there has been a mutation to an important part of a chromosome. Mutations can be inherited
or they can happen spontaneously during conception. There are two kinds of testing: screening and diagnostic. A screening test is a blood test that indicates the probability that the pregnancy has a
chromosome abnormality. It is noninvasive, meaning there’s no possibility of harm to the pregnancy to have this blood test drawn. For women for are low risk, a blood test is drawn from the mother in the first and second trimester. A woman is typically considered low risk if she will be under age 35 at delivery, hasn’t had a prior pregnancy with a chromosome abnormality, and has no family history of genetic abnormalities. Six types of blood markers are evaluated, and this information is combined with an early ultrasound
evaluation of the fetus to give a risk estimate
for how likely it is that the fetus will have
an extra chromosome. Women age 35 and above or who have a personal or family history of having a baby with a
chromosome abnormality or who have screened positive with the low risk blood test are considered high risk
for a genetic disorder. High risk women have the option for cell-free DNA testing. This is also a noninvasive blood test to evaluate the risk of
chromosome abnormalities, but it has a lower risk
of false positive results. It’s a more expensive test and it’s typically covered by insurance for women who meet the high risk criteria. Importantly, both kinds of screening tests can be falsely positive or, more rarely, falsely negative. If a screening test is positive, the option will then be given to follow up with a diagnostic test for a definitive diagnosis. A diagnostic test uses a tiny sample of your placenta or the
fluid around the fetus to directly measure the
chromosomes that the fetus has. There are two ways to do this: either through chorionic
villus sampling, or CVS, or amniocentesis. Both tests are done by a maternal fetal medicine specialist in their office. No anesthesia is required. Chorionic villus sampling is when a needle is used to take a tiny
sample of the placenta, either through the abdomen
or through the cervix. The placenta has cells with chromosomes that usually match the fetus. It can be done between 10 and 13 weeks of gestation. In an amniocentesis, a
needle is used to sample some of the amniotic
fluid around the fetus. The amniotic fluid carries cells that have chromosomes matching the fetus. It can be done after
15 weeks of gestation. Both methods carry a very
small risk of pregnancy loss, typically around one in 450 to one in 900, depending on the
gestational age of the fetus and the experience of the
provider doing the procedure. Because both methods sample
the actual chromosomes, very detailed testing is available and the results are highly accurate. Genetic screening is optional. It’s your choice whether to undergo prenatal testing. Even if you have a positive screen, you don’t have to undergo
diagnostic testing. On the other hand, there are some parents who desire to skip the screening and move straight to diagnostic testing. It can be helpful to think how you would use the results of the prenatal screening test. For some parents, the information may lead them to end the pregnancy. For others, having the information would help them to prepare for having a baby with a genetic disorder and plan for the medical
care their child may need. Other parents may not want to know this information at all before the child is born. We are fortunate to live at a time when this kind of testing is available and you, as a patient, have choices. At each step, it’s important to discuss with your provider any questions or concerns you have so that you feel empowered to choose what is right
for you and your family.

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