Prenatal diagnosis involves detecting (usually hereditary) abnormalities in the unborn child. A well-known example of this is research into the presence of Down syndrome in the unborn child. Women who become pregnant at an older age have an increased risk of having a child with this syndrome. The choice of whether or not to have research carried out can be particularly difficult, partly because one may be faced with a dilemma if an abnormality is found. A number of tests in this area include chorionic villus sampling, amniocentesis and NIPT.
Table of contents
- What is Down syndrome and what is the risk of the unborn child developing the condition?
- What forms of prenatal diagnosis are available?
- Follow-up research
- Reason for research
- Considerations for prenatal research
Portrait of child with Down syndrome / Source: Centers for Disease Control and Prevention, National Center on Birth Defects and Developmental Disabling, Wikimedia Commons (Public domain)
What is Down syndrome and what is the risk of the unborn child developing the condition?
Down syndrome is a congenital condition. Children with this syndrome have an intellectual disability and an increased risk of physical abnormalities resulting in health problems. The consequences of the syndrome for intelligence and the body vary greatly per individual.
Every human cell contains chromosomes and they contain hereditary information (DNA), for example about eye color and the structure of proteins. Normally a cell contains 46 chromosomes. Down syndrome involves a so-called extra 21st chromosome (trisomy 21). In the Netherlands, for every 180 thousand births, approximately 300 have the syndrome. A pregnant woman with an unborn fetus with the syndrome has an increased risk of having a miscarriage. After birth there is also an increased risk of the child dying. Other less common forms of chromosomal abnormalities that are also screened for are Patau syndrome (trisomy 13) and Edward syndrome (trisomy 18). Care for people with the syndrome has improved greatly in recent decades. About half of people with Down syndrome reach the age of 60 or older.
Risk of having a child with Down syndrome
|
Mother’s age at time of test |
Chance of having a child with Down syndrome per 10,000 births |
|
20-25 years |
11-13/10,000 (0.1%) |
|
26-30 years |
14-19/10,000 (0.1-0.2%) |
|
31-35 years |
20-45/10,000 (0.2-0.5%) |
|
36-40 years |
60-155/10,000 (0.6-1.6%) |
|
41-45 years |
200-615/10,000 (2.0-6.2%) |
What forms of prenatal diagnosis are available?
Prenatal (Lat.: pre-: before, natalis: birth) diagnostics can be divided into research into infectious diseases/blood groups and research into genetic/chromosomal abnormalities. This article only discusses the latter.
Prior to the examination, a consultation always takes place with the obstetrician, general practitioner or gynecologist. They will provide information about the method of the test, its limitations and added value and about follow-up research. It is a combination test, which means that two different tests are performed. Based on this, a statement is made about the risk that the unborn fetus has the syndrome. If the risk is increased, the suspicion can be confirmed by a final test: the follow-up test. Unfortunately, a reduced risk does not guarantee that there will be no abnormalities.
The blood test
The blood test is the first part of the combination test. Blood is taken from the mother and the levels of the hormones called beta-HCG and PAPP-A are determined, this allows a statement to be made about the risk.
Ultrasound examination baby 12 weeks old / Source: Wolfgang Moroder, Wikimedia Commons (CC BY-SA-3.0)
Nuchal translucency measurement by ultrasound
The thickness of the nuchal fold of the unborn fetus is measured using ultrasound. It is a thin layer of fluid present under the skin of the neck. This layer is also present in a child without an abnormality; an increase in its thickness increases the risk of a chromosomal abnormality. In the case of multiple births, the risk can be determined per individual.
These two tests result in a statement regarding the risk of an abnormality. In the Netherlands, a chance of 1 in 200 or higher is described as increased (0.5%). If there is an increased risk, this may be a reason to obtain confirmation through additional diagnostics.
Follow-up research
There are various methods for follow-up research to confirm or rule out the suspicion. These consist of chorionic villus sampling, amniocentesis and, since April 1, 2014, the so-called NIPT study.
Chorionic villus sampling (‘Chorion biopsy’)
This test can be performed between the 11th and 14th week of pregnancy. A small piece of placental tissue is removed via the abdominal wall or vagina using an ultrasound-guided puncture (with a long needle). This tissue looks flaky, hence the name. 99% of the time it contains cells from the unborn child. The results are usually known within two weeks. Disadvantages are a slightly greater chance of miscarriage and, compared to amniocentesis, more often an unusable result. The advantage is a relatively early result, which makes any abortion less physically stressful.
Anatomical overview of pregnancy / Source: Blausen.com staff, Wikimedia Commons (CC BY-3.0)
Amniocentesis (‘Amniocentesis’)
The amniocentesis is taken after the 15th week of pregnancy. A small amount of amniotic fluid (approximately 15-20 milliliters) is collected via the abdominal wall using an ultrasound-guided puncture. The child’s cells found here can be used to investigate the presence of hereditary disorders. Advantages are a relatively low number of miscarriages compared to chorionic villus sampling (approximately 3 per 1000 procedures) and very high reliability of the test result. A disadvantage is carrying out the research at a later stage, as the abortion is usually more physically and mentally stressful compared to an earlier period. Some mothers already indicate that they feel alive during this period.
NIPT
NIPT is an abbreviation for Non-Invasive Prenatal Test, it is a form of blood test on the mother that makes it possible to examine the child’s DNA. This test examines the child’s DNA. If no abnormalities are found, it is virtually ruled out, while if abnormalities are found, confirmation by amniocentesis or chorionic villus sampling is still recommended. In April 2014, a study was started into the results obtained through this test. As far as is known, this test does not increase the risk of miscarriage.
Reason for research
A reason for conducting research is an increased risk of the presence of chromosomal or hereditary abnormalities in the child, which include:
- Mother with an older age (36 years or older)
- Previous birth of a child with a chromosomal abnormality
- An abnormal result of the ultrasound result made after 20 weeks
- A miscarriage twice or more in the past (possibly due to a chromosomal abnormality)
- The prevention of hereditary disorders in the mother, father or immediate family members, such as cystic fibrosis or hereditary muscle disorders
- An increased risk of damage to the unborn child due to medications that the mother cannot discontinue during pregnancy, such as certain types of anti-epileptic drugs
Considerations for prenatal research
Abortion
Based on the results of a follow-up test, a decision can be made to terminate the pregnancy (abortion). This is a very difficult emotional decision. The choice is accompanied by a lot of guilt and the feeling of powerlessness. The emotional consequences are comparable to the severity of a spontaneous stillbirth. In the Netherlands and Flanders there are contact groups for fellow sufferers, they can often provide a lot of support and explanation.
Deviation but not abortion
If one is of the opinion that an abortion is absolutely not an option, for example based on religion, conducting research can still be of added value. This way, one can better prepare for the birth itself, which has an increased risk of a complicated course. In addition, people are prepared for a different child than one would initially expect. The disadvantage of doing follow-up research, however, is that there is an increased risk of miscarriage.
Voluntarily
All steps in the research process are completely voluntary, it is not mandatory to undergo the diagnostics and you can decide to interrupt the research process at any time. In addition, people are free to choose what to do with the results.
To ask
Questions that one can ask themselves regarding the choice of whether to perform prenatal research include:
- What would life be like with a child with Down syndrome?
- Is a chromosomal abnormality a reason to terminate the pregnancy?
- Do the benefits of the follow-up examination (the knowledge about the presence of an abnormality) outweigh the risk (with an increased risk of miscarriage)?
Additional information
The RIVM is a reliable source for finding substantive information, the Erfo Center can help make a choice and the Down Syndrome Foundation (SDS) can provide an idea of what a chromosomal disorder entails.
