Prenatal Testing

Until a few years ago there were two studies that could indicate whether an unborn child had a chromosomal abnormality (e.g. Down syndrome): chorionic villus sampling and amniocentesis. These tests were offered to pregnant women 36 years or older because their risk of such a deviation is greater than for younger mothers. Moreover, in both tests the interference could cause a miscarriage (1 in 200) and that risk in younger women is higher than the probability of a deviation.

In recent years a test was developed that can estimate the probability of a chromosomal abnormality without risk of a miscarriage. This test can make a more reliable risk assessment than the hitherto used age limit. The Deputy Minister of Health has still decided to hold on to the age limit, so for younger women (younger than 36 years) the tests will not be reimbursed. However, her opinion is that all pregnant women should be able to make them the choice of they want to get tested or not. If an increased risk is found after doing the probability test, there must be decided what to do with that risk. The only way to be certain about the presence of a deviation is still a amniocentesis or chorionic villus sampling.

The goal of prenatal testing is discovering chromosomal abnormalities. Such deviations can not be cured. For example, if the child is found to have Down syndrome, the parents have a choice. They can prepape for a child with Down syndrome, or they can choose to terminate the pregnancy.

The test without risk which currently is the most reliable, is the combination test. This test involves an ultrasound and a blood test done around the twelfth week of pregnancy. When going for the ultrasound they will look at the so-called nuchal translucency thickness of the baby. There also will be searched for proteins in the blood of the pregnant woman. The combination of these two studies then provides a risk assessment of the risk of a chromosomal abnormality in this specific pregnancy.

When you get the results of the risk assesment you can for example get a probability of 1 in 1200, 1 in 500 or 1 at 30. A chance of 1 in 200 or higher (e.g. 1:100, 1:50) is seen as an increased risk. With an increased chance you will get the opportunity to do a chorionic villus sampling or amniocentesis. In a less than 1 in 200 chance that further research will not be reimbursed. The word probability says it all, it is not a certainty. With a probability of 1 in 1200 chances are very small but not zero. A chance of 1 in 30 is significantly increased but remember that out of those 30 women 29 will get a child with no deviations, which is still by far the highest probability. The disadvantage of the combination test is that the younger a woman is, the more likely one is to get a false negative as a result. Because the only way to know for certain is doing chorionic villus sampling or amniocentesis (with the associated risk of miscarriage), this may be a disadvantage for younger women.

Besides the combination test, there is the opportunity to make a detailed ultrasound done around 20 weeks gestation. Here the size of the baby will be measured and the child is viewed more globally (are the vertebrae closed? Is the lip closed? Are there four heart chambers?). This echo will be reimbursed.

The above shows clearly that there are several aspects to the prenatal testing. For each person, the balance of pros and cons are different. Many pregnant women want to hear that all is well with their child. It is important to realize that there never can be given guarantees about the health of a child. The test only looks at a fraction of all possible deviations and because the probability there will be no definitive answer. Moreover, the interpretation of the probability outcome and the possible choices after give a lot to think about. To use the test solely as reassurance, can thus give a lot of disadvantages.

It is also important to consider how great the likelihood of chromosomal abnormalities really is. When do you think about deviations you might almost forget that the vast majority of children born are completely healthy. The boundary of the test results lie in a probability of 1 in 200. Roughly you can say that for women younger than 36 years the probability is under 1 in 200, less than half percent. At age 36, the probability is around 1 in 200 and then rises with age to approximately 1 in 50 at age 40, which is 2 percent.

Questions that a pregnant woman herself (and her partner) can ask are:

- How do I feel about having a child with a defect in my family?
- How do I feel about the risk of miscarriage when choosing to do a chorionic villus sampling or amniocentesis?
- Would I terminate the pregnancy if any defects where found?
- How high does a probability have to be for me to consider it high risk, and can I live with that risk?

The answers to these questions will ofcourse be different for each person. That is exactly the reason it is so hard to give advice in these sorts of situations. Eacht pregnant woman must use her own judgement in making these decisions, because she will have to live with the consequences of them. During the first appointment we can provide, if you want, with information about the different prenatals tests.

If there are cases of deviations or defects in your family (including yourself) of which you think can occur to your child, call us for information or contact the ERFO-line of the VSOP (organisation of parents and patients with hereditary or congenital disorders at 035-6028555.

For making an appointment to have a combinationtest, you can contact Verloskundig Echocentrum Ite Boerema at 020-6166990 (www.echoamsterdam.nl), preferably around the ninth week of your pregnancy.

For the rates of the echo practice, click here.

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