Peter O’Leary: Testing questions

A NON-invasive prenatal test that identifies Down syndrome through the analysis of fetal DNA within the mother’s blood has become available in the past 2 years.

Many providers now offer this test as an alternative to first trimester screening (FTS) or as the next step following a high-risk FTS result. The major benefits of a non-invasive prenatal test (NIPT) are reductions in the numbers of invasive diagnostic procedures and procedure-related miscarriages in high-risk women at modest additional cost to the health system.

Five NIPTs are now commercially available in Australia via overseas laboratories.

Currently in Australia, a majority of pregnant women access FTS to identify fetal anomalies. This involves ultrasound (nuchal translucency) and biochemical measurements (maternal serum free β-hCG and PAPP-A) to determine a gestational age-related risk for Down syndrome, Trisomy 13 or 18. Currently, those women found to be at high risk are offered invasive diagnostic testing such as amniocentesis, which carries a small risk of miscarriage.

Research conducted by a team I led at the Curtin University’s Centre for Population Health Research reviewed 32 478 singleton pregnancies screened between January 2005 and December 2006 in WA.

The research showed that if all pregnant women identified as at high risk had access to NIPT, more cases of the genetic disorder could be confirmed during pregnancy at less than 10% additional cost — $56 360 per confirmed case of Down syndrome compared with the current cost of $51 372 per case.

However, Medicare does not cover the costs of NIPT investigations.

What are the implications for current prenatal screening services?

First trimester ultrasounds will remain a key component of prenatal screening as they provide early indications of severe structural abnormalities of brain, heart, kidney, skeleton and stomach. Improved detection rates and lower screen positive rates can be achieved by the additional biophysical (nasal bone, tricuspid regurgitation) and biochemical markers (alpha fetoprotein, placental growth factor) or the adjustment of cut-offs for risk assessments.

Currently, requests for NIPT are coming from a relatively small number of informed women who are prepared to pay the total service cost. However, as the benefits of NIPT become more widely known — lower numbers of diagnostic interventional procedures and reduced procedural-related fetal losses — the broader community may pressure the government to provide equitable access to prenatal NIPT screening in Australia.

The cost of introducing universal NIPT is prohibitive and so current opinion supports providing NIPT to women whose pregnancies are identified at increased risk by FTS. However, the overall detection rate will not increase simply by introducing NIPT as a second-tier screening option.

The benefits of NIPT in terms of higher detection rates will require modifications of FTS strategies by adjusting risk cut-offs, additional markers or quality improvements.

Before NIPT becomes omnipresent in Australia, forward planning processes should be established for oversight, evaluation and monitoring of prenatal screening for fetal anomalies.

In European countries, for example, governments have established joint government-professional advisory bodies comprising feto-maternal specialists, epidemiologists and policymakers to address the emerging technical, ethical, legal, social and economic challenges of population genetic screening.

The UK National Health Service has shown how national coordination and centralised monitoring can improve all components of prenatal screening performance, including ultrasound, biochemistry and risk reporting through a standardised quality improvement process.

In Australia, a national expert body could advise the federal Health Department on issues, policies and strategies to support system improvement and influence the delivery of prenatal screening services across jurisdictions.

These activities should be underpinned by monitoring and the evaluation of evidence supporting current practices and the introduction of new prenatal screening techniques such as NIPT.
 

Professor Peter O’Leary is the deputy director of health sciences at Curtin University and chairs the university’s Human Research Ethics Committee.