Early in your pregnancy we will ask you to decide which, if any, testing you wish to perform to check for chromosomal problems such as Down’s syndrome. There are several choices available and hopefully this will provide some insight into which is best for you.
A normal fetus will have two sets of 23 chromosomes making a total of 46. Having a missing or extra chromosome creates major developmental problems and usually results in early miscarriage. Chromosomal problems are rarely hereditary, they are usually caused by division errors early in embryonic development and can happen randomly to any couple, although the incidence of division errors increases with increasing maternal age. The chance of a diagnosing a chromosomal problem at age 35 is about 1/200 and at age 40 is about 1/50. Since many chromosomal problems end in miscarriage prior to diagnosis, the true incidence is actually quite a bit higher.
All of our patients are offered screening for Trisomy 21 (Down’s syndrome), Trisomy 18, and Trisomy 13, regardless of their age. In trisomy conditions the fetus has a whole extra chromosome, which has very serious effects. Trisomy 21 is often compatible with life but other trisomies are universally incompatible with life outside the uterus. While a fetus could be trisomic in any chromosome, we focus on these three trisomic conditions (an extra chromosome 21, 18 or 13) since they are the most common ones that survive past the first trimester.
There are several options available for screening for these conditions. The first option is called “Ultrascreen”, which combines nuchal fold measurements (an ultrasound measurement of the fold on the back of the baby’s neck done at 11-14 weeks) with a blood test to assess risk for chromosomal problems. A large nuchal fold can be associated with chromosomal problems and some heart defects. The associated blood test can be done from 9-14 weeks and measures several proteins, which may be altered in cases of chromosomal abnormalities.
Ultrascreen picks up 91% of Down’s Syndrome and 95% of trisomy 13 and 18. The down side is that there is a high false positive rate, since the test is read as “abnormal” when the calculated risk of a chromosomal problem is greater than 1/270. So frequently we counsel patients that the test was “abnormal” even though the great majority of so called “abnormal” tests turn out to be normal after definitive testing is done. This is obviously quite stressful for the patient. When the Ultrascreen is abnormal we offer the patients an amniocentesis, which extracts a small amount of amniotic fluid from around the baby with a small needle. Fetal cells can be isolated from this fluid and directly tested, making amniocentesis 100% accurate.
A second screening test is called “Harmony”. Harmony is a blood test best done at 11+ weeks, which analyzes fetal DNA in maternal blood and provides a risk assessment for Trisomy 21, 18, and 13. Gender analysis can be added for an additional fee since the presence of the Y chromosome (indicating a boy) can be detected. This is 99% accurate. If the Harmony is abnormal an amniocentesis will be offered to give 100% accuracy.
For patients who choose Harmony we recommend doing the nuchal fold ultrasound measurement in addition to the Harmony test, as the nuchal fold can detect problems that are not part of the Harmony test (such as Turner’s syndrome and certain heart defects).
Thirdly, many patients choose to do neither option, which is very reasonable as we cannot intervene to change the situation when a baby has a chromosomal problem (other than termination), so some argue that there is no point in checking. We certainly respect that decision and present it as an option to all of our patients.
One of the key issues when choosing a test surrounds insurance coverage. Ultrascreen is less accurate but has been around longer so is better understood by insurance carriers. We have found that all major carriers cover Ultrascreen when mom is over 35, and most carriers cover it even for patients under 35. Harmony is more accurate but is also a newer test and is still considered “experimental” by some carriers, so is generally not covered for patients under 35. Since this test is done by an outside lab (not our office) we cannot guarantee coverage and we let all our patients know that the full cost of Harmony is $795 or $815 with the gender test, and to be prepared to pay that amount in case it is not covered. We recommend discussing this with your individual plan before you make a decision.
Our providers and insurance specialists are here to help you work through these options and decide what is right for your family.
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