Non Invasive prenatal testing

Question 1

What is Non Invasive Prenatal Testing(NIPT)?

Answer 1

• It is a term to describe a simple blood test to identify whether a foetus has Down Syndrome
• The accuracy rate of picking up Down Syndrome (trisomy 21) is 99.5%, Edward Syndrome (trisomy 18) is 99% and Patau Syndrome (Trisomy 13) is 79-92%

Question 2

How does NIPT work?

Answer 2

• Blood test from 10 week gestation
• It tests cell free DNA in the maternal plasma to assess fetal genetic material
• The samples are sent off shore to China or America
• $ 500-1400 depending on the provider
• Results in 2 weeks for trisomy 21, 18 and 13
• Sex of the foetus and sex chromosome abnormalities can be checked
• A positive test is always confirmed by invasive testing (Karyotype)
• An assay failure or low DNA pool of the foetus (<4% ) can lead to no result being issues. This is more common with increased maternal weight (>160kg-about 50%)
• NIPT should not be used if the pregnancy has been conceived with a donor egg
  *

Question 3

What are the benefits of the current Down Syndrome screening compared to NIPT?

Answer 3

• This is a 11-13 weeks gestation US looking for nuchal translucency and a blood test for placental protein A (PaPP-A) and free B HCG.
• Detection rate of 90% and false positive rate of 3%.
• It provides more information than just the risk of trisomies in the form of correct dating, diagnosis of multiple pregnancies, chorionicity and anatomy assessment to detect major abnormalities
• Many structural abnormalities are detected by this method including cardiac and others
• Low PaPP-A levels have been associated with adverse pregnancy outcomes including foetal loss, pre-term birth, IUGR and preeclampsia
• It is cheaper than NIPT

Question 4

How to incorporate NIPT into current clinical practice?

Answer 4

• Counselling patients about the high sensitivity of this test for Down, Edward and Patau Syndrome
• All positive results need to be confirmed by an invasive test
• Cost to be mentioned (500-1400)
• Test failure rate of 4% needs to be mentioned
• US to exclude structural foetal abnormalities is still very important and hence recommneded
• It can also check for foetal sex and sex chromosome abnormalities
• The American College of Obstetricians only recommend NIPT for pregnancies at high risk of aneuploidy
• It has not been validated for multiple pregnancies
• The ethical issues of termination due to recognition of foetal sex and affordability have been raised