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Down’s syndrome - testing in pregnancy


Autor: ass dr Milan Stefanović    

down’s-syndrome-testing-in-pregnancy

Down’s syndrome is a disorder, caused by inadequate distribution of chromosomes (trisomy of the 21st pair). It is manifested in mental retardation and specific physiognomy: obliquely positioned cuts of eyelids, prominent epicanthic folds, small brachycephalic head, wide hands, short little finger, small concha, open mouth, red cheeks, irregular teeth disposition…

However, like other people, they differ from each other by their appearance, characteristics and abilities. While they are babies, it is difficult to determine how much they will be ill when they grow up. Some people with Down’s syndrome are able to get a job and lead a relatively independent life; however, the majority needs help and support in the long run. Maximum possible mental development reaches the level of an eight-year old child. In most of the cases, persons with Down’s syndrome live for 50 years, but some of them can live for more than 70 years. Alzheimer’s disease (a form of senile dementia) begins earlier in these persons than in other people.

How frequent is Down’s syndrome?

People usually don’t expect their baby has Down’s syndrome. It does not occur often in a family. Once, it was assumed that only older women can get a child with Down’s syndrome. However, this is not true. Any woman can get a child with Down’s syndrome, but the risk is bigger with the woman’s age; the older the woman, the greater the possibility that she will get a child with Down’s syndrome. For example, the probability of getting a child with Down’s syndrome is 1 to 1500 (0.07%) in women who are 20 years of age; 1 to 900 (0.1%) in women who are 30 years of age; 1 to 100 (1%) in women who are 40 years of age.

What causes Down’s syndrome?

Inside all the cells of the body, there are tiny structures, called chromosomes. They carry genes which determine the way of our development. Majority of people have 23 pairs of chromosomes in every cell. While our body produces special cells, necessary for reproduction, pairs of chromosomes are distributed and rearranged. Sometimes, these pairs are not regularly distributed and because of that, the baby’s cells have the additional copy of the chromosome number 21. This causes Down’s syndrome, and because of that, this syndrome is also called Trisomy 21. The additional chromosome cannot be removed from the cells; therefore, this disease cannot be cured. The irregular distribution of chromosomes happens by accident and it is not caused by the parents’ actions.

A test on Down’s syndrome during pregnancy

Most of women want to know whether their baby has Down’s syndrome. Information about testing can be of great help in making this decision.

There are tests that give the precise information and they are called diagnostic tests. However, these tests increase the risk from miscarriage. Therefore, they are not recommended to all women. Instead, they are carried out in two stages. In the beginning, all women are recommended the tests which do not carry a risk from miscarriage. This kind of teat is called “ screening test”. It does not provide a definite answer, but tells us whether there is a higher risk from this disease. After that, the women with the higher risk can be offered a diagnostic test. If the result of the screening test is between the values-one in two and one in 250- a diagnostic test should be done. (the risk of 1 to 250 is at the same time the risk of 0.4%).

It is important to understand that screening tests cannot show with certainty whether the baby has Down’s syndrome or not. They can only be used in order to avoid the risk of carrying out of unnecessary diagnostic tests. It is up to the woman herself to decide whether she will undergo these tests or not. If she decides to do the screening test, and is later recommended to do the diagnostic test, she decides by herself whether she will undergo the tests or not.  

What kind of information does the screening test give?

All the tests that will be described later give results in the form of  1 in ….For example : 1 in 100 or 1 in 1500, etc. the same result can be expressed in percentage. These values can tell what the probability that the baby will have Down’s syndrome is. That is hoe, the result 1 in 100 means that one of hudred babies has the chance to have Down’s syndrome. The result 1 in 1500 shows that there is the probability that 1 in 1500 babies has this syndrome. To simplify, the larger the second number, the lower the disease. Next, we are going to explain how it can be decided on the further course of examination on the basis of the screening test results.


Women who no longer need examinations

if the screening test shows that the risk is lower than 1 in 250, we are not going to insist on diagnostic tests. Most of the screening test results (about 95%) belong to this category and represent the results of low risk. Low risk means exactly this; it does not mean that the risk doesn’t exist at all; it means that the probability is lower than in 1-to-250 result, which is the limit to further examinations.

Here, there is still a low probability that some children with Down’s syndrome were not detected by screening method. This happens if the expected model is not recognized in blood testing or scans, because of small natural difference. All in all, ¼ of the babies with Down’s syndrome was not discovered by screening tests.

Women who need further examinations

If the screening test result shows that the risk is greater than 1 in 250 (for example, 1 in 100), it is recommended to carry out a diagnostic test. Such screening test results are sometimes marked as high-risk results. One in twenty women (5%) has these results.  

Types of the screening tests

Blood testing

Blood testing determines the amount of the substances which naturally exist in the mother’s blood. These substances pass from the baby onto the mother. The mother’s blood sample is usually taken between the 10th and the 20th week of pregnancy. The time of testing and information about the substances vary among different institutions. A computer program determines the results of blood testing, together with the mother’s age, bodily weight and lasting of pregnancy in order to determine the probability of Down’s syndrome. In Nis, the following tests can be carried out: Double screening test (11 to 14 weeks of pregnancy) and Triple screening test (14 to 20 weeks of pregnancy).

Ultrasound screening

Nuchal thickness scanning. It is a special ultrasound examination, carried out between 11 and 14 weeks of pregnancy. It determines the amount of liquid, under the skin of the baby’s neck. Computer program processes these data, the size of the baby and the mother’s age in order to determine the risk of the syndrome. As the test is based on individual measures of the baby, it can be used with twins and triplets and determine the risk for each baby individually. It is known as the NT test.

Combined screening in late pregnancy

Integrated test is based on the information which is got by the nuchal thickness scanning, together with the results of the two samples of blood- the first is taken in the 10th week, whereas the second is taken in the 15th week. The complete results are not determined until the second blood testing is done.

If the screening test result shows a higher risk of the syndrome, there are two possible options. The first is the refusal of the diagnostic test, which can be very stressful for the pregnant woman, since she will think about the screening test results by the end of her pregnancy. The second option is the diagnostic test, with the fact that there is a slightly increased risk of miscarriage. There are two types of diagnostic tests-examination of chorional villi and amniocentesis.  

Amniocentesis is carried out from the 16th to the 18th week of pregnancy. It is a widely used procedure which lasts about 10 minutes. The whole procedure is carried out under the control of ultrasound and it includes putting a needle through the abdominal wall into the uterus and taking about 20ccm of the fetus water. In it, there are the baby’s cells which are further examined in order that the chromosomal feature of the baby could be made. Among 100 samples, one is inadequate for any definite conclusion because the cells don’t grow or the results are unclear. In that case, amniocentosis should be repeated or in late pregnancy, cordocentesis should be carried out – examination of the baby’s cells from the blood from the navel cord.  
Amniocentesisi is successfully carried out in Nis for almost three years in the pregnancy pathology department, at the gynaecological-obstetric clinic.

The examination of chorional villi is carried out from the 11th week of pregnancy. It is usually carried out in specialized centers. Here, ultrasound is also used in order to follow the movement of the needle, no matter whether the needle is injected through vagina or abdomen. By taking the placental tissue, the necessary sample from the laboratory analysis and counting of the baby’s chromosomes is provided. Similarly to amniocentesis, here two among hundred samples do not show the definite result.

Both procedures are not completely safe and they are not recommended to all women. Among 100 women, who underwent this procedure, one of them will have miscarriage, and two of them will have miscarriage while the examination of chorional villi.

The procedures themselves are painful, though some women consider them unpleasant. Day or two after the intervention, the women are advised to avoid all the activities that include bending, stretching and lifting. In the lower part of the stomach, the feeling of uneasiness can appear and last for a day or two. This is normal. The pain will be eased with the use of paracetamol.  

How long should one wait for the results?

The results are complete in 18 days. Some hospitals suggest new molecular tests, as a part of diagnostic tests, and they are known by their initial letters FISH and PCR. Thanks to them, you can arrive at some information after two or three days, but it is still necessary to wait for 18 days to pass in order to get the complete results.

The results can be presented to the patient in many ways depending on the agreement with the doctor. There is a chance that the result shows that the baby doesn’t have Down’s syndrome; but, what if the result tells the opposite? Because of that, every patient should think about the way in which she would want to hear this information and face the problem. The patient can be told about the results at home, too, as well as at the clinic, by the telephone conversation or a letter. In our town, the results are told to the patient directly, at the Children’s internal department, in whose laboratory this examination is carried out.

Diagnostic test results

The most usual result is that the baby doesn’t have Down’s syndrome. To some women, this information is enough, and they do not ask any further questions, while other women want to talk about the results with the doctor. They want to know the reason why the screening test results, on one hand, and the diagnostic test results, on the other, don’t match.

As we have already mentioned, by the use of the screening test, we can see whether it is necessary to recommend the patient the diagnostic test or not. Screening tests indicate that there is a certain type of model with blood testing and ultrasound examination. This model can sometimes be found in babies with Down’s syndrome. The problem is, it can be found with normal pregnancies, as well. The results of the tests vary a little, depending on different physiological states. The pattern is recognized by the use of the screening tests, but not the reason that brought this pattern about. Only the diagnostic test can determine whether the cause of the results is the existence of Down’s syndrome in the baby. When a woman undergoes the diagnostic test, and the result shows the baby doesn’t have the syndrome, the previous results of the screening test are considered to be false positive results.  

The baby does not have Down’s syndrome, but there is another – the crucial point of amniocintesis or examination of chorional villi is to discover Down’s syndrome. However, with the examination of the baby’s chromosomes, other variations can hardly be noticed. Some of them can be very serious, while others can hardly affect the baby. If the tests show this problem, the woman must turn to genetics consultant.
The baby has got Down’s syndrome- a small number of test results show this; in that case, there are three options which depend on the parents.
Some people decide to keep the baby, preparing themselves for the problems they will have to face with, raising a child with Down’s syndrome. Others decide to adopt a child because they find themselves incapable enough to raise the child with this problem. Some women decide to have abortion.

Any person faced with this problem has to make the right decision for it. Women will have the possibility to talk with the doctor about all possible options; besides that, additional support and information can be found outside medical help. They will have enough time to make the right decision and the doctor’s support, regardless of this decision.



Milan Stefanovic, MD, TA


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