Non-Invasive Prenatal Screening (NIPS)

NIPS is a relatively recent development and addition to the range of screening tests available in early pregnancy. It is a maternal blood test with no associated direct risk to the pregnancy and offers early potential diagnosis of the commoner chromosome abnormalities (such as Down Syndrome) and potentially in higher risk patients the early diagnosis of uncommon genetic abnormality (such as microdeletion syndromes).

The basis for such a technique is that fetal DNA products from placental tissue are able to cross the placenta into maternal blood and be detected and counted using gene sequencing technology. Pregnancies affected with some chromosome abnormalities such as Down Syndrome will produce differences in the expected amount of such DNA products and the difference allows for a likelihood calculation to be made for the presence of the abnormality.

The technique is highly sensitive for the detection of Down Syndrome or Trisomy ( >99.8%of cases will be identified ) and with rates approaching this level for the detection of Trisomies 18 and 13 (also known as Edwards and Patau Syndromes). Determination of the fetal sex is part of the test overall result. The test is offered by several local pathology providers who perform the test under licence from one of the 5 world wide patent holders for the test. The difference between all is minor and all function with similar high detection levels for Down Syndrome. Accordingly we are happy to have the test performed by all of the providers.

The test is performed at any time beyond 10 weeks gestation and the results will generally be available in 5-7 working days. The amount of fetal DNA within the specimen is important with regard to the performance of the test. Where the fetal fraction of cell free DNA is below 4% the test result should not be interpreted and the blood retaken. This occurs in less than 5% of tests and repeating the test almost always results in obtaining an adequate specimen.

Very rarely a second specimen will also contain insufficient DNA and a result will not be possible (in this situation there will be no charge to repeat the test). The cost for the NIPS is generally between $350 and $450. No Medicare rebate is currently available for this testing.

In the event of an abnormal NIPS result confirmation by performing an invasive test (CVS or amniocentesis) is recommended.