Should you consider NIPT?
Should all pregnant women have Non-Invasive Prenatal Testing (NIPT)? Three of Hong Kong's leading obstetricians share their views.
Dr Charas Ong Yeu-theng
Consultant obstetrician and gynaecologist at The Women's Clinic, and subspecialist in maternal and fetal medicine
I would recommend that everyone does NIPT. It's a very primitive form of screening if you just screen the high-risk group. The majority - that is, the absolute number - of Down's syndrome affected babies come from the younger reproductive age group and not the advanced maternal age group because the younger age group have more babies.
But you cannot just do NIPT straight away. You need to do a screening scan to complement NIPT: to date the pregnancy, to screen for multiples, to measure nuchal translucency and to check major gross abnormalities.
For certain gross abnormalities, you don't need NIPT, you just go for an amniocentesis or CVS directly. Cystic hygroma [abnormal growths that appear on the baby's neck or head] is one classic example.
One fear is that NIPT may become a direct-to-customer service, which I don't think is the way to go. I think NIPT has to be done with an obstetrician who is comfortable with the counselling and knows about the ins and outs of NIPT.
Dr Danny Leung Tse-ngong
Director of Hong Kong Sanatorium's maternal and fetal medicine department, and president of the Obstetrical and Gynaecological Society of Hong Kong
If the pregnant woman is younger than 35, we'll give them the option of Oscar or NIPT. I tell them the sensitivity and false-positive rate of Oscar, the cost of the tests and their limitations. If the woman doesn't mind paying more for a more sensitive test, we can just go for NIPT. If the woman is over 35, we'll give them the option of NIPT or invasive tests [amniocentesis or CVS].
There are some women who want the invasive test because they would rather have a miscarriage than miss anything. I have to put it into perspective; everybody wants more, but then you pay for the risks.
I wouldn't say that all women have to do NIPT, but sometimes I'd recommend it. For example, if the woman is 40 and the ultrasound shows the nuchal translucency is 3mm, then almost for sure the Oscar result will be high-risk. So it'll save you more money if you go directly to NIPT and skip the Oscar.
Sometimes the woman should skip NIPT and go for CVS directly. For example, when the ultrasound shows an absence of the nasal bone or the nuchal translucency is huge [6mm].
So, the ultrasound does have value before NIPT. It's intelligent to use that to triage. The NIPT is a very good test, but it's very important for the clinician to discuss it with the woman. The test can't replace clinicians.
Dr Lucy Lord
Specialist in obstetrics and gynaecology at Central Health Medical Practice
When you are counselling people about prenatal diagnosis, there are two important aspects: first, are they low-risk or high-risk? Second, what would they do with the information? You have to get to know your patient and make sure that they understand that if there's no chance they would terminate the pregnancy, that some of these tests are not appropriate because they're expensive, anxiety inducing and not going to resolve issues.
For high-risk/would terminate, if you're over 35 a NIPT test is quite helpful as it will give you the earliest accurate indication that you might have a problem, or reassurance that you don't have one. We'd do NIPT at nine weeks and an anomaly scan at 12 weeks to detect structural abnormalities that you might miss if you only did NIPT.
For low-risk/would terminate, we might do the Oscar test first and then offer NIPT to the people who turn out to be high-risk.
For low-risk/wouldn't terminate, we'd assure them that likely they would be normal, that there's no benefit to them being anxious by doing a whole load of tests.
We'd recommend them to do an anomaly scan at 12 weeks because it has a very low false-positive rate and is also able to pick up things such as severe spina bifida.
We don't recommend NIPT for everybody. The counselling is crucial and, as an obstetrician, I think it's important to have a very clear view about the science and the technical aspects, but also a very broad mind about the psychological and emotional issues that are in many respects more important than the science.
- The International Society for Prenatal Diagnosis accepts that, with suitable genetic counselling, NIPT can be helpful for women who may have been determined to be at high risk by one of the previous recommended screening strategies.
- The society does not endorse the ad-hoc use of NIPT in women at low risk, outside a formal protocol that considers the overall best combination of tests, their impact on screening performance, and patient acceptability.