Prenatal diagnostics: cost, methods and detectable disorders

“Prenatal diagnostics” (PND) refer to prenatal screening. However, not all pregnancy examinations are classed as prenatal diagnostics: they do not include regular urine tests, antibody tests of the mother’s blood or ultrasound examinations. Prenatal examinations during pregnancy are more for detecting hereditary diseases. These include chromosomal abnormalities or rare diseases that run in the family and occur as a result of changes in individual genes.

In short, prenatal diagnostics or screenings are voluntary examinations performed by specialists in addition to the regular pregnancy check-ups.

When are prenatal diagnostics performed?

The first prenatal diagnostics examination is usually the first trimester screening. This method of prenatal diagnostics is voluntary. In which week of pregnancy is it carried out? Doctors usually carry out this prenatal examination between the 11th and 14th week of pregnancy. 

If the results of the screening warrant it, additional examinations may follow. You should talk to your doctor about potential risks in such cases.

There are two broad PND approaches: invasive and non-invasive methods. Which of these tests are most suitable for you depends on your individual situation. Your doctor can provide you with advice.  

Invasive prenatal diagnostics

Invasive prenatal diagnostics deliver reliable results long before birth. “Invasive” means that the examinations involve intervention in the body of the expectant mother. Invasive methods of prenatal diagnostics enable a gene and chromosomal analysis. Invasive methods include:

• Chorionic villus sampling for prenatal diagnosis: Your gynaecologist will take some tissue from the placenta using a needle. This procedure is carried out starting from the 11+0 week of pregnancy. The aim of this is to examine the chorionic villi, small finger-like protrusions on the placenta, which enable direct contact between the mother’s and the child’s blood.
• Amniocentesis for prenatal diagnosis: In an amniocentesis, the doctor takes some amniotic fluid from the placenta using a needle. This procedure is carried out starting from 15+0 week of pregnancy. To do so, they insert the needle through the abdominal wall and the uterine wall.
• Cordocentesis for prenatal diagnosis: The specialist uses a needle to penetrate the abdominal wall of the expectant mother, where they take a sample of the blood of the unborn child. Cordocentesis can be carried out from the 20th week of pregnancy.

Non-invasive prenatal diagnostics

Non-invasive tests do not require any risky interventions in the body. One example is the first trimester screening between the 11th and 14th week of pregnancy. This examination shows whether the child is at increased risk of being born with a chromosomal abnormality. In this, the doctor analyses various factors which they compile into an overall picture:

• The age of the pregnant woman plays a role in prenatal diagnostics. The older the expectant mother is, the greater the likelihood of chromosomal abnormalities.
• Blood tests are another method of non-invasive prenatal diagnostics. Specific blood hormone and protein levels are significant here.
• Ultrasound examinations are another key component of prenatal diagnostics. Doctors use the results of several of these examinations to make a diagnosis. The nuchal fold scan is one such type of prenatal diagnostics. If the nuchal translucency is increased, the unborn child is at an increased risk of being born with chromosomal abnormalities or other disorders.

In addition to first trimester screening, prenatal diagnostics also include NIPT, non-invasive prenatal testing. Several of these tests are approved in Switzerland. The doctor takes a blood sample from the pregnant woman from around the 10th week of pregnancy. Small quantities of foetal DNA are found in the mother’s blood. This means laboratories can detect possible chromosomal abnormalities and genetic disorders of the foetus directly in the mother’s blood. This method of prenatal diagnostics can also determine the gender of the child. By law, doctors cannot tell you the gender until after the 12th week of pregnancy.

Note: a positive NIPT result does not constitute a definitive diagnosis. If, in such cases, the expectant mother is considering terminating the pregnancy, further, invasive examinations are mandatory.

Medical specialists can use these various methods of prenatal diagnostics to detect a range of disorders and genetic defects or to make a preliminary suspected diagnosis. The most common types of anomalies include:

• Trisomies: Prenatal diagnostics can provide insight into chromosomal disorders like trisomy 13 (Patau syndrome), trisomy 18 (Edwards syndrome) and trisomy 21 (Down syndrome).
• Spina bifida: Doctors can detect spina bifida using a prenatal examination during pregnancy. This involves taking a blood sample from the expectant mother and testing it for alpha-fetoprotein. An amniocentesis is also possible.
• Noonan syndrome: For the prenatal diagnosis of this genetic defect, doctors perform chorionic villus sampling or an amniocentesis.
• Cystic fibrosis: Prenatal diagnostics offer methods of antenatal screening for cystic fibrosis. Options include chorionic villus sampling or amniocentesis. This is offered if both parents carry the relevant gene variance in their DNA.
• Prader-Willi syndrome: Amniocentesis or chorionic villus sampling are also suitable for the prenatal diagnosis of this genetic defect.
• Achondroplasia: Doctors can use prenatal diagnostics to detect potential achondroplasia – a type of genetic dwarfism.
• Brittle bone disease: Doctors can use ultrasound to make a suspected prenatal diagnosis. Further examinations may follow. 
• Autism: Researchers have found that there are potential signs of autism that can be detected by specialists in prenatal diagnostics using ultrasound. These may for example include abnormalities in the heart and lungs. Affected children may be at increased risk of autism spectrum disorder. Important: this is not a reliable diagnosis method. It merely points to a trend.

Prenatal diagnostics have certain advantages. Specialists can use these examinations to detect serious disorders which must be treated during pregnancy or immediately after birth (e.g. spina bifida). Some of these disorders rule out the child’s chances of survival. In such cases PND gives those affected scope for a decision, which they should ideally discuss directly with a doctor.

Prenatal diagnostics also have disadvantages. For instance, invasive prenatal diagnostic methods are associated with a risk of miscarriage. In addition, positive test results cause anxiety in expectant parents and present them with ethical challenges.
 

Prenatal examinations in pregnancy can provide key insights into the health of your baby. Ideally, you should discuss with your doctor whether or not prenatal diagnostics are suitable in your case. Research the facts thoroughly and make the right decision for you and your child.

This page was produced in collaboration with the Cada fertility clinic in Zurich. Cada offers specialist advice and support for people who want to have children.