Prenatal screening tests                                                                                                              

(examples: NIPT (non-invasive prenatal testing), such as the Harmony test, ultrasound, first trimester screening)                

  • Evaluate the chance for certain conditions in a pregnancy
  • Pose no risk to the pregnancy    
  • Are followed by additional testing if a diagnosis is desired
  • Performed as early as 10 weeks of pregnancy
  • May indicate an increased chance for a condition in an unaffected pregnancy (“false positive”) or a low chance for a condition in an affected pregnancy (“false negative”)

Prenatal Diagnostic tests

(Amniocentesis, CVS (Chorionic Villus Sampling))

  • Can diagnose and/or rule out certain conditions in pregnancy
  • More definitive and comprehensive than prenatal screening tests
  • Invasive and pose a risk of pregnancy loss
  • Performed at 10-13 weeks (CVS) or 15-20 weeks (amniocentesis) of gestation
  • Cannot detect or rule out all genetic or chromosomal conditions

The Harmony test using cell-free DNA

  • Looks at fragments of your baby’s DNA in your blood
  • Can be done as early as 10 weeks of pregnancy
  • Screens for trisomy 21 (Down syndrome), trisomy 18 and trisomy 13
  • High detection rates (> 99% detection rate for Down syndrome)2
  • Low false positive rates (less than 1 in 1000 for trisomy 21, trisomy 18 and trisomy 13)2

Nuchal Translucency Ultrasound

  • Ultrasound to measure the size of an area behind the baby’s neck called the nuchal translucency (NT)
  • Done between 11-14 weeks of pregnancy by a certified practitioner
  • Typically used in combination with blood tests to screen for chromosomal conditions1
  • Can identify some major birth defects, but cannot rule out the presence of birth defects
  • Does not replace a second trimester ultrasound evaluation

Taditional first trimester screening using ultrasound and blood draw

  • NT ultrasound combined with blood marker analysis
  • Performed in 9-14 weeks (blood test) and 11-14 weeks (NT ultrasound)
  • 1 in 20 women receive a false positive result1
  • Results from 5 days to 3 weeks depending on the time of blood draw and NT ultrasound 

 

References

  1. ACOG Committee on Practice Bulletin No. 163. Obstet Gynecol. 2016 May;127(5):e123-37
  2. Stokowski et al. Prenatal Diagn. 2015; 35:1243-1246

What prenatal diagnostic tests are available?1

Amniocentesis

  • Amniotic fluid around the fetus is collected using a needle
  • Baby’s chromosomes from the cells in the fluid are studied in a lab
  • Done between 15-20 weeks of pregnancy
  • Risk of procedure-related miscarriage about 1 in 160 to 1 in 9002,3

CVS

  • Cells from the placenta (chorionic villi) are collected using a needle
  • Chromosomes from the placental cells studied in the lab
  • Done between 10-13 weeks of pregnancy
  • Risk of procedure-related miscarriage about 1 in 140 to 1 in 4502,3

References

  1. ACOG Committee on Practice Bulletin No. 163. Obstet Gynecol. 2016 May;127(5):e123-37.
  2. Mujezinovic et al. Obstet Gynecol. 2007;110(3):687.
  3. Akolekar et al. Ultrasound Obstet Gynecol 2015; 45:16-26.

References

  1. ACOG Committee on Practice Bulletin No. 163. Obstet Gynecol. 2016 May;127(5):e123-37.
  2. Mujezinovic et al. Obstet Gynecol. 2007;110(3):687.
  3. Akolekar et al. Ultrasound Obstet Gynecol 2015; 45:16-26.