Prenatal Screening & Testing
NIPS: Non-invasive Prenatal Screening or Cell-free DNA
The most common reason a pregnant woman will see a maternal-fetal medicine specialist in pregnancy is to check the developing baby for abnormalities prior to birth. Unfortunately, not all abnormalities can be detected, however, those that can be detected fall into 2 general groups:
1. Malformations or structural problems with the body of the fetus or
2. Genetic defects in the fetus.
Some fetuses with genetic defects also have structural malformations, but not all. For example, about 30% of fetuses with Down syndrome have no structural defects making it very difficult to detect with ultrasound alone. This is why genetic screening is done. Genetic screening in pregnancy is called “screening” because these tests do not detect all cases of genetic abnormalities. However, screening tests have no risk for the fetus (they are blood tests of the mother). In many pregnant women, multiple different screening tests are performed in an effort to detect as many abnormalities as possible.
The first screening test a woman may have in pregnancy is called NIPS or non-invasive prenatal screening. This blood test can be performed any time after 9-10 weeks of pregnancy. It is sometimes performed by your doctor in the office, so if you are not sure if you have had this test, you should ask your doctor. This blood test measures DNA from the fetus in the blood of the mother. There is no risk to your baby from having this test. It is very accurate (99%) for detecting Down syndrome (also called trisomy 21), Edward syndrome (trisomy 18) and Patau syndrome (trisomy 13).
This test can also detect several syndromes that occur due to microdeletions such as DiGeorge syndrome or Cri-du-chat syndrome (accuracy here is difficult to determine). This test cannot detect all genetic defects. It does not replace or give you nearly as much information as CVS or amniocentesis. It can tell you the gender of your fetus, if you desire.
Unfortunately, this test is not always covered by insurance because it is a new test. It is more likely to be covered if you are >35 years old, have an abnormality in your fetus or if you miss one of the other screening tests. You should check with your insurance to see if this test is covered.
The following are >99% detected
• Trisomy 21 (Down syndrome)
• Trisomy 18 (Edwards syndrome)
• Trisomy 13 (Patau syndrome)
• Trisomy 15
• Trisomy 16
• Trisomy 22
• Monosomy X (Turner syndrome)
• Trisomy X
• Klinefelter syndrome (XXY)
You may ask yourself
“Isn’t there a genetic test that is 100% accurate in pregnancy?”
There is – these tests are called
CVS and amniocentesis, they
are called diagnostic tests (see Diagnostic Testing). Unfortunately, in pregnancy, these diagnostic tests have a small risk for the fetus so not every woman wants to take a risk.
Nuchal Translucency Screen
Fetal nuchal translucency screen is performed between 10 and 14 weeks of gestation. It is a screening test for Down syndrome (trisomy 21), Edward syndrome (trisomy 18) and Patau syndrome (trisomy 13). These 3 conditions are all associated with developmental delay, and sometimes malformations in the newborn, therefore many parents want to know if these problems exist as early as possible. If your fetus is too big or too small, the test cannot be performed and will have to be rescheduled, so timing is very important.
The test has two parts. First, an ultrasound is performed which may be across the abdomen or across the vagina, or both, depending on the position of the fetus. The fetus is measured to make sure it is the right size and examined with the ultrasound. We check to make sure everything looks like it is developing normally. As the fetus is only about 5-7 cm (the size of large shelled peanut), not every problem can be seen. Dr. Minior will make sure there are 2 arms and two legs, 2 hands and 2 feet, and development of the face, brain, chest and abdomen looks normal. The nuchal translucency, which is a fluid space in the back of the neck of the fetus, is then measured. A normal nuchal translucency is less than 3 mm. If an abnormality is detected, Dr. Minior will review this information and its implications with you.
When the ultrasound part of the test is concluded, your blood will be drawn. The results of the ultrasound part of the test and the blood get sent to the lab, and after a week or so, a report will be faxed back to your referring doctor. The doctor will review the results with you in the office. The results are reported in the form of an odds that the fetus is affected with Down syndrome, such at 1:5 or 1:10,000. These odds can help you decide if you want to undergo any further testing in your pregnancy.
The nuchal translucency screen is about 98% sensitive to detect Down syndrome. This means that it picks up 98% of cases and misses 2%. It is 95% sensitive to pick up trisomy 13 or 18. This test can now also tell you the gender of the fetus (this is 95% accurate). The added advantage of the nuchal screen is that it provides a very early assessment of the fetus for major defects in the body structure (anomalies or malformations), some of which may be lethal at birth.
Sequential Screen (formerly called the Quad screen)
The Sequential screen measures the level of several markers in maternal blood. These include alpha-fetoprotein (AFP), unconjugated estriol, human chorionic gonadotropin (hCG), and inhibin A. The results can be combined with the results from your nuchal screen to increase detection rates for Down syndrome. This test is performed between 15-22 weeks. The best time to perform this test is between 16-18 weeks. This test is often done in your OB doctor’s office, so if you are not sure if you have had the test you should ask your referring doctors office.
This test screens for:
Neural tube defects (spina bifida)
If this is the only test you have done, it detects about 80% of Down syndrome. If this test is combined with the nuchal screen, it detects 93% of Down syndrome. This test detects about 75% of neural tube defects.
Diagnostic Testing in Pregnancy (CVS or Amniocentesis)
Some patients decide following screening tests, ultrasound findings, their family history or their own personal beliefs that diagnostic testing provides the level of reassurance that they desire. In these cases, there are two options for more definitive testing: CVS and amniocentesis. CVS is performed at 13 weeks. Amniocentesis can be performed between 16-22 weeks. These tests are an option for any patient that wants the most complete information available about their pregnancy.
Both tests provide the same type of results:
Karyotype – Counts every chromosome pair in the fetus. Rules out Down syndrome, trisomy 13, trisomy 18, Turners syndrome and Klinefelter’s syndrome and every other condition where there is an abnormal number of chromosomes with essentially 100% accuracy.
Chromosomal microarray testing – Identifies smaller “submicroscopic” abnormalities in DNA, particularly duplications or deletions that lead to developmental delay or malformations in the baby. This test identifies >180 genetic or syndromic conditions that can be associated with developmental abnormalities.
FISH testing – A rapid test performed on the sample that is usually available in 2 days. The FISH test looks for the 5 most common chromosome abnormalities and is 98% accurate.
In approximately 2-3% of CVS tests, the result needs to be verified by amniocentesis.
Both CVS and amniocentesis are associated with a small risk (1:1000) for miscarriage.
Additional Services & Specialties
We offer leading-edge prenatal ultrasound to all pregnant women throughout pregnancy. We specialize in early diagnosis, evaluation and treatment of complex prenatal complications.
From routine to complicated cases, we provide gynecologic ultrasound with careful attention to your personal comfort. You will receive results from Dr. Minior on the day you are seen.
CENTER FOR TREATMENT OF DIABETES IN PREGNANCY
DIABETES TREATMENT CENTER
Advanced expertise in education, management and treatment of diabetes in pregnancy including diabetic counseling & surveillance and Nutrition counseling
A sub-specialty of obstetrics that focuses on the diagnosis and treatment of expectant mothers and their babies as well as care of pregnancies complicated by high risk conditions.