Fetal Testing Overview

Desert West OB/GYN — Fetal Testing Information

Please read this important information carefully

Birth defects affect about 3% of all pregnancies. Some, but not all, of the possible birth defects can be detected by blood tests, ultrasound, Chorionic Villous Sampling, and/or Amniocentesis.

The testing that you decide to perform for your pregnancy is optional and is your individual choice based on many factors such as your health, age, previous pregnancy experiences, and family health history.

The two types of testing are screening and invasive.

Screening Tests — These tests have no risk to the fetus or the mother, include blood tests and ultrasound. While they don’t give a yes or no answer, they can identify a woman who is at higher risk of having a baby with specific birth defects.

  • Free cell DNA testing is available.
  • The Ultra-Screen is performed between 10 weeks 3 days and 13 weeks 6 days. This test includes a finger prick blood test combined with an ultrasound measurement of nuchal translucency (fluid under the skin at the back of the neck). This testing can detect up to 90% of trisomy 13, 18, and 21. Other birth defects can be detected, as well. False positive rate is about 5%.
  • Alpha-fetoprotein (AFP) is a blood test drawn at 15-20 weeks (optimal time for highest detection rate is 16-18 weeks) to screen for possible neural tube defects (Spina Bifida and Anencephaly). This test may be ordered in addition as a follow up to the Ultra-Screen.
  • The Quad Screen is a blood test drawn at 15-20 weeks.  This blood test estimates your risk of having a baby with a neural tube defect, Trisomy 18, or Trisomy 21.  Detection rate is about 80%.  False positive rate is about 5%.
  • A routine obstetrical ultrasound should optimally be performed at 18-20 weeks gestation to detect any structural abnormalities.  The ultrasound can detect about 50% of all major fetal birth defects and up to 75% of Down’s Syndrome.
  • Cystic Fibrosis screening is a blood test used to detect the presence of the Cystic Fibrosis gene.  Cystic Fibrosis can cause digestive problems and excess mucus production of the lungs.  Both the mother and the father have to carry the gene for the child to possibly be affected.  This is more prevalent in Caucasians and Ashkenazi Jews.
  • Invasive Tests — These tests include Chorionic Villous Sampling and Amniocentesis, have a very small risk to the fetus and an extremely rare risk to the mother.  These tests are usually reserved for women 35 years or older or for women with a positive screening test.
  • Chorionic Villous Sampling (CVS) is performed between 10-12 weeks gestation and obtains placental tissue to identify chromosomal abnormalities.  It has a risk of miscarriage of 1 in 100 and provides the earliest definitive answer.
  • Amniocentesis is performed at 15-22 weeks gestation. This test obtains amniotic fluid under ultrasound guidance to identify chromosomal abnormalities.  In addition, AFP levels are measured to test for neural tube defects. This test has a risk of miscarriage of 1 in 400.
  • It is important to identify fetal testing options as early as possible during your pregnancy.  After identifying your choices, we will work with you to implement your plan.  Insurance coverage for prenatal testing may vary depending upon your insurance carrier.