Non-invasive prenatal screening (N.I.PS test) has been available to Australian women through their Private Obstetrician for more than three years and has revolutionised the way to screen for conditions such as Down’s Syndrome. The test was initially processed in California for a fee of nearly $2000 per sample. Now the test is completely processed here using the same advanced the technology with results available usually within five days for approximately $450.
NIPS is one of the most complex technological and accurate tests in medicine currently. It involves a blood sample from the mother after 10 weeks gestation after a previous ultrasound to confirm the number and viability of the fetus. The mothers blood contains cell free DNA from both herself (the majority) and the baby’s placenta. The DNA is floating freely in the blood from a process of natural cell rupture. Approximately 3-10% of the free DNA belongs to the fetal placental origin. This fetal DNA is smaller in size and can be separated by complex scientific equipment for analysis. NIPs testing for Downs Syndrome and other related genetic abnormalities involves a volume based analysis of the ratios of the 23 different types of human DNA pieces and the sex chromosomes X and Y. The test will therefore also report accurately the sex of the fetus from 10 weeks gestation! A triple copy of number 21 Chromosome results in Downs Syndrome. The NIPS test will detect more than 99% of Down’s Syndrome affected fetuses, and have similar sensitivity for other genetic conditions it currently screens for, including Edwards Syndrome and Patau’s Syndrome. It will detect many other DNA quantitative abnormalities, but does not currently screen for other well-known conditions such as Haemophilia, Cystic Fibrosis or Fragile X Syndrome.
Screening for Down’s syndrome for the previous 15 years has been performed by a risk assessment method. This involves two biochemical markers in the blood being measured at 10 weeks gestation, the age and past history of the mother, and the ultrasound measurement of the fetal neck fat thickness at 12 weeks gestation. This is reported as a result such as 1:1500 chance of Down’s Syndrome. The biochemical risk assessment detects 93-95% of Down’s syndrome. Comparing the biochemical test to the new NIP’s test leads to the finding that the NIPs test is superior in the detection of Down’s Syndrome and only marginally less sensitive than the invasive amniocentesis which is still available as a test for confirmation.
Occasionally the NIPs test cannot be utilized because of a demised twin being present which contaminates the DNA in the mother’s blood. However, it can be utilized in twin pregnancy, IVF pregnancy and donor egg or sperm pregnancy.
Results return to my office from the laboratory daily and my midwives will call you with results and ask you whether you wish to know the sex of the baby. This has been an exciting new development in caring for couples in their journey to establishing their family. If you have more queries, please call my office and talk to my midwives who will be more than happy to assist.
Every pregnancy has a small chance of a baby being born with a genetic condition. Prenatal testing occurs during pregnancy for some of these conditions but not all. This screening is available to provide you with more information about your unborn baby. Prenatal screening is optional and generally occurs in the earlier stages of pregnancy.
The principle of screening is to offer a safe, accessible test to identify a pregnancy with an increased chance of having a baby affected by a chromosomal or genetic condition. It is important to understand that a screening test does not tell you definitively if your baby has a condition, only if there is an increased chance. Also screening tests are not 100% guaranteed and may miss some babies that have a condition.
Known family carried conditions can be specifically screened for with blood tests.
Recessive genetic conditions can be randomly screened for in limited ways. Recessive conditions are genetically hidden if a person carries just one of the two altered genetic DNA required for the pure condition. If both parents happen to have these altered DNA pieces then potentially some of the their children can be affected. All of these more serious conditions affect less than 1/2500 children born in Australia.
Currently in Australia testing for cystic fibrosis, spinal muscular atrophy and Fragile X syndrome is commercially available as a single package (Approx. $350) through pathology centres. Beyond that, there are tests for packages of up to 400 genetic abnormalities, all of which are significantly less common than 1/2500. This cost is approx. $800.
Cell-free DNA screening or non-invasive prenatal testing
Cell-free DNA screening, or non-invasive prenatal testing (NIPT), uses a sample of your blood to estimate the chance of your baby having a chromosomal condition such as Down syndrome. This screening for spontaneous genetic conditions (not carried by the parents) is available for limited conditions. The most common condition is Down Syndrome and the majority of couples choose to screen for this. An 11–13 week ultrasound is not included with this test and has to be arranged separately if you decide to have one.
Only a diagnostic test, such as an amniocentesis or chorionic villus sampling (CVS), can definitely tell you whether your baby has a genetic or chromosomal condition. As diagnostic tests carry a small risk of miscarriage, most women have a screening test first before deciding if they wish to have diagnostic testing. It is important to remember that even a normal amniocentesis or CVS result cannot guarantee a ‘perfect’ baby. There are many conditions that cannot be detected before a baby is born. More information about amniocentesis and CVS can be found on the RANZCOG website under Patient Information.
Your doctor should be able to discuss the available screening and diagnostic tests with you. You may be referred to a genetic counsellor if you require additional support and information. Women who have previously had a child with a chromosomal or genetic condition should receive individualised counselling from a specialist clinical genetics service, preferably before getting pregnant.