Paging Dr. Grunebaum: What Prenatal Tests Should I Expect in My First Trimester?
If you are pregnant for the first time, you may be surprised by how many tests your OB-Gyn runs throughout your pregnancy. It can be a bit overwhelming to keep track of what each one is testing for, and what tests should take place during each trimester. Even if you’ve already gone through this process one, two or (like me!) three times, tests may have been added since your last go-round – or maybe you just simply can’t recall what happened when! I’ve asked Dr. Grunebaum of BabyMed.com, Director of Obstetrics and Chief of Labor & Delivery at NewYork-Presbyterian Hospital/Weill Cornell Medical Center, to give us an overview of all the tests you’ll take , and what they mean. Here, he weighs in on the first trimester tests for Down Syndrome and other chromosomal issues.
Prenatal Testing: Testing for Down Syndrome and Other Chromosomal Issues in the First Trimester
Like most moms-to-be, you want assurances about your and the baby’s health and you want to have the right tests done to ensure you get the information you need. That’s where prenatal testing comes in. Seeing your doctor during pregnancy involves many things, but more importantly it includes a whole list of tests to check on the mother’s and the baby’s health.
Prenatal testing can detect many, but not all, conditions. Knowing about your baby before birth can be helpful in making decisions, and these prenatal tests are the most reliable way to find out about any health issues you or your baby may have.
Nuchal Translucency Test
Around 11-13 weeks of the pregnancy a screening for Down’s syndrome is usually offered to all pregnant women. The test is known as the “first trimester screen” or nuchal translucency test.
This test consists of two parts:
- An ultrasound to measure the thickness of the back of the fetus’ neck and
- A blood test that detects the presence of 2 markers in a blood sample in conjunction wit blood tests that measure levels of pregnancy-associated plasma protein-A (PAPP-A) and a hormone known as human chorionic gonadotropin (HCG).
These three tests are then combined to calculate the risks of having a fetus with a chromosomal anomaly. Abnormal levels of PAPP-A and HCG or an abnormally thick neck may indicate a problem with the baby. If the test shows an increased risk, additional tests such as CVS (chorionic villi sampling) or amniocentesis can be done to confirm a diagnosis.
The current nuchal screening test has a false positive rate (that is, the results suggest a problem when the fetus is in fact healthy) of around 3-4%.
This means many women have invasive testing, using chorionic villus sampling (CVS) or amniocentesis. Both of these procedures carry a less than 1 in 2-500 risk of causing a miscarriage.
Recently Added Test
There is now a new screening technique which is a simple blood test that involves analyzing the small amounts of fetal DNA found in the mother’s blood stream, circulating cell-free DNA extracted from a maternal blood sample. The test can be done as early as 10 weeks of the pregnancy. It takes about 2 weeks for results to be ready and as more companies offer the test, it has become more widely available. The test detects the relative amount of 21, 18, 13, X and Y chromosomal material, so if you desire, you can find out the gender of the baby as early as 11 weeks.
After testing 1,005 women, researchers found the new technique had a much lower false positive rate (around 0.1%). This means many fewer normal pregnancies had an unnecessary invasive diagnostic test with the new test. However, in about 2% of women the new test did not produce a result, meaning that the conventional screening technique had to be used.
For now, most professional organization recommend it only for women at risk, such as when you are 35 years or older or have other risks.