Important Prenatal Fetus Tests You Should Ask Your Doctor About
by Suzanne Robin, RNMay 01, 2014
Photograph by Twenty20
When you're pregnant, the question of whether your baby is developing normally is of primary concern. Prenatal testing can provide an answer in many cases. Some tests require nothing more than a blood sample or abdominal ultrasound, while others require more invasive testing methods. Talk to your doctor about prenatal testing, particularly if you have a family history of certain genetic defects or other risk factors.
The least invasive testing method, abdominal ultrasound, involves no more discomfort than that caused by a full bladder. A level 1 or screening ultrasound may be done as early as the first few weeks of pregnancy, or your doctor might wait until later in the first trimester. A level 2 ultrasound, a more in-depth look at the fetal tissues, is generally done around week 20. A level 2 ultrasound can detect around 70 to 80 percent of congenital defects, compared to around 15 to 20 percent with a level 1 ultrasound, Adventist Hinsdale Hospital reports.
Quad Marker Screening
The quad screen is a blood test that checks the levels of four substances: alph-fetoprotein, produced by the fetal liver; unconjugated estriol, produced by the fetal liver and placenta; human chorionic gonadotropin, or hCG, produced by the placenta; and inhibin A, another hormone produced by the placenta. The test, normally done between weeks 15 and 20 of pregnancy, can detect neural tube defects, such as spina bifida and anencephaly, with 75 percent accuracy, says the Cleveland Clinic. Quad screening can also diagnose approximately 75 percent of genetic and chromosomal disorders, such as Down syndrome and trisomy 18, in women younger than 35 and up to 90 percent in those older than 35. In these cases, further testing with ultrasound or amniocentesis may be needed.
A new blood test can identify trisomies, which include chromosomal abnormalities such as Down syndrome and trisomy 13 and 18. Accuracy rates are highest for Down syndrome and trisomy 18, at 99 and 96 percent, respectively, according to a May 2014 article in "Contemporary OB/GYN." This tests measures the levels of cell-free fetal DNA in a pregnant woman's blood. Because the fetal fraction of cells in maternal blood increases after 9 weeks, testing is done after this time. This screening is not yet widely available, so your doctor may need to refer you elsewhere for testing.
If you have a family history of a genetic disorder or want reassurance that your baby is free of suspected birth defects or congenital conditions, diagnostic procedures such as chorionic villus sampling and amniocentesis can give you answers. These tests study fetal cells to detect abnormalities. Chorionic villus sampling, commonly known as CVS, samples fetal cells taken from the placenta and is done earlier in pregnancy, around 10 to 12 weeks. Amniocentesis, which tests amniotic fluid, is usually done between weeks 15 to 18, according to the Centers for Disease Control and Prevention. Because these tests increase the risk of miscarriage and may contribute to birth defects, counseling is required to weigh the pros and cons.