Paging Dr. Grunebaum: What Prenatal Tests Should I Expect in My First Trimester?
Recently, Dr. Grunebaum of BabyMed.com, Director of Obstetrics and Chief of Labor & Delivery at NewYork-Presbyterian Hospital/Weill Cornell Medical Center, to gave us an overview of the prenatal tests to expect in your first trimester, including the new Harmony Blood test (available here). Today he fills us in on the second trimester and third trimester testing you should expect.
Second Trimester Pregnancy Tests
The second trimester of the pregnancy begins around 13 weeks and ends around 27 weeks of the pregnancy. There are several important tests done during this important time period:
Quad/Triple Screen: Multiple Marker Screen and Maternal Serum Alpha-Fetoprotein Screening (MSAFP)
These are blood tests usually done between 15 and 20 weeks of pregnancy. The MSAFP test measures the level of a protein called alpha-fetoprotein which is being produced by the fetus. In creased AFP levels indicate the possibility of neural tube defect or other problems and decreased AFP levels indicate a possible fetus with Down syndrome. The AFP test is a screening test, which means that abnormal levels may indicate an increased risk, though most times additional testing shows the fetus to be normal. The triple marker test measures blood levels of three substances: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3). And the Quafd test adds a test for the hormone inhibin A as well. When this compound is added to the test, the detection rate for Down syndrome increases to between 67 and 76 percent in women younger than 35. The triple and quad tests are screening tests requiring additional tests to confirm an abnormality in the fetus.
An amniocentesis is a diagnostic test. It is a procedure performed after 16 weeks of pregnancy, usually between 16 and 18 weeks of pregnancy, but can be done at any time afterwards too. It is done by inserting a needle through the woman’s abdomen into the amniotic sac under sonographic guidance and withdrawing about 15-20 cc of amniotic fluid that contains fetal cells. Amniocentesis is safe, resulting in less than 1 in 500 miscarriages if done by an experienced doctor. The test can detect neural tube defects and genetic disorders such as Down syndrome or other conditions and can detect nearly 100% of certain genetic abnormalities.
An anatomy sonogram or ultrasound is a non-invasive diagnostic procedure done around 20 weeks of the pregnancy usually to detect fetal malformations. It checks for fetal anomalies, and in many cases is also when the sex of the baby is confirmed. Most ultrasound examinations detect over 50-60 % of major fetal malformations.
Cervical length screening
The cervical length screening test is an ultrasound test using a transvaginal ultrasound probe that can be done as early as 18 weeks of the pregnancy to check the cervical length to detect patients at increased risk for premature births. The shorter the cervix measures, the higher the risk of premature birth. The test is usually done for high risk patients such as those with prior premature births, or those with symptoms of premature labor.
Glucose screening is a test for diabetes and is usually done between 24-28 weeks of the pregnancy. This test consists first of a screening test called 1-hour glucose challenge test (GCT) which measures your blood-sugar level an hour after you’ve had a glass of a special glucose solution. If the test is elevated, then you take another diagnostic glucose tolerance test (GTT) in which you drink a higher glucose solution on an empty stomach and have your blood drawn before the test and then every hour for 3 hours. If two of the four glucose values are elevated then you are diagnosed with gestational diabetes and require further treatment and tests.