Non-Invasive Prenatal Testing (NIPT)
The ability to assess the fetus for the common chromosomal problems (eg. Trisomy 21, Trisomy 18, Trisomy 13) by assessing the amount of cell-free fetal DNA in the mother's blood (Non-Invasive Prenatal Testing or NIPT) is now available. This new form of testing is highly sensitive for detecting Trisomy 21 (detection rates >99%) and may be performed at virtually any time in the pregnancy from 10 weeks gestation onwards. Most NIPT has been performed in women at increased risk of chromosomal problems (eg an increased risk First Trimester Screening risk, women > 35 years of age who are pregnant), although a recent large American study published in 2015 has demonstrated strong performance characteristics in the general obstetric population.
The advantage of NIPT is the avoidance of an amniocentesis or CVS if the pregnancy has an increased probability for chromosomal problems - an amniocentesis is only required if the maternal blood test indicates an increased amount of free fetal DNA for one of the chromosomes tested. It is important to recognise that NIPT is a high-level screening test and therefore may be associated with false positive results (ie. reporting there is a problem when in fact there is not) and false negative results (ie. saying all is well when it is not). The chance of a false positive result increases in women who have NIPT when their pregnancy is at very low risk of a chromosome problem (ie a risk >1:2,000). If ultrasound shows a problem with the fetal appearances that may indicate a possible chromosome problem, NIPT is not recommended, but rather a diagnostic test such as CVS or amniocentesis.
For those women who select NIPT as a primary screening test for chromosome disorders, an early fetal anatomy survey at 12-14 weeks gestation is recommended to confirm pregnancy dating, excluded some severe fetal anomalies and to ascertain placental chorionicity in multiple pregnancies. There is no need to have combined First Trimester Screening if NIPT has already been performed. Ideally, the early fetal anatomy survey ultrasound should be performed after the NIPT results are available.
NIPT is now performed in Australia and is able to be accessed by women who desire this form of chromosome screening using some local pathology providers. Womens Imaging Services can assist women in accessing NIPT after specific counselling. The medical staff at Womens Imaging Services has no contracts with any of the companies providing NIPT. The NIPT costs $395-850 (depending upon the particular service provider and the technique used) with no Medicare rebate. Once blood is drawn it will take 5-8 working days before a result is available. In 3% of women a result will not be available from the first blood draw (particularly if you are very overweight) and a redraw is required.
A current position statement on Non-Invasive Prenatal Testing is available from the International Society for Prenatal Diagnosis.
Further information on NIPT in Australia may be accessed from the pathology providers supplying the testing:
Western Diagnostic Pathology