Prenatal diagnosis via ultrasound, CUB, nuchal scan and other examinations

All examinations and tests available to women during pregnancy are voluntary. Of course it is reassuring to find out that the pregnancy is progressing normally. But there is also a risk of having to make difficult decisions if the examination detects chromosome abnormalities or deformities.

Some parents-to-be find it reassuring to find out how things are progressing, while others feel it creates unnecessary worry during the pregnancy.

Do what feels right for you. You can always contact your midwife or doctor if you feel unsure and need more information. There are various methods for prenatal diagnosis. All examinations and tests offered are voluntary. 

Ultrasound scan
An ultrasound scan is offered to all women in weeks 18 to 20 of pregnancy. It is a simple, safe, painless examination where you get an ultrasound image of the foetus.
During an ultrasound scan, high-frequency sound waves are transmitted to the uterus through the abdominal wall. Sometimes, especially in early pregnancy, scan can be done through the vagina. The scan produces images of the womb, the foetus, the amniotic fluid, the placenta and the umbilical cord.

The latest ultrasound equipment is capable of producing three dimensional images of the foetus in the womb. These images allow a more detailed medical examination as they show all the minutest details and structures of the foetus.

An ultrasound scan shows the following things:
• The foetus's size.
• The foetus's heart activity.
• How the pregnancy has developed.
• How far the pregnancy has progressed.
• How many foetuses are in the womb.
• The placenta's position in the womb.
• Whether the foetus has all the vital organs.
• Whether the foetus has any visible deformities.

Additional ultrasound scans are sometimes offered to check that the baby is developing normally. Whether and when this is done depends largely on where in Sweden you live. It should be stressed that an ultrasound scan alone is not 100 percent reliable. If an abnormality is suspected, further examinations are always performed.

The Swedish Radiation Safety Authority's recommendations regarding ultrasound
According to the Swedish Radiation Safety Authority, a foetus should only be exposed to ultrasound for medical purposes. The precautionary principle dictates that a foetus should only be photographed, filmed or have its gender determined for reasons of medical importance.

CUB - combined ultrasound and biochemical screening
The CUB test is carried out between weeks 11 and 14 of pregnancy. The ultrasound test measures the thickness of the skin at the back of the foetus's neck. This measurement is combined with the results of a blood test in which the pregnancy hormones free beta-hCG and PAPP-AA are measured. The likelihood of Downs Syndrome is calculated and examined by specially qualified doctors and midwives.

The result of the CUB test is not regarded as 100 percent conclusive. To conclusively confirm a hormone disorder, the amniotic fluid or the placenta must be tested. The CUB test is not available to all women; it depends on where in Sweden you live. If you want a CUB test, you can discus it with your midwife.

Nuchal translucency scan
This test measures something called nuchal translucency. The thin layer of fluid under the skin of the foetus's neck is measured by means of ultrasound. All foetuses have this fluid in their neck, but an abnormally thick layer signals a higher likelihood of a chromosome disorder.

An even more accurate result is obtained by having a blood test a few days prior to the nuchal scan. When the ultrasound scan and blood test are combined, it is referred to as a CUB test (see above).

An amniocentesis can be performed if there is a higher than normal risk of chromosome abnormalities. The doctor inserts a fine needle into the uterus and withdraws a small sample of amniotic fluid, which is analysed. Amniocentesis can be performed in week 15 at the earliest. The test carries a small risk of miscarriage. The risk is estimated to be approximately 0.5-1%.

Chorionic villus sampling
An alternative to amniocentesis is chorionic villus sampling. It is available to pregnant women with certain hereditary diseases, or if there is a high risk of chromosome abnormality. This test can be performed from week 11 of pregnancy and is recommended if the doctor deems it important to screen early. Chorionic villus sampling carries a higher risk of miscarriage. The risk is estimated to be approximately 0.5-1%.

Other tests to examine the foetus
The pregnant woman can be given a blood test to detect whether she has antibodies against blood types other than her own. The mother's blood and the amniotic fluid can also be analysed to look for antibodies against various viruses. Later in the pregnancy, if the foetus is not growing normally, the blood flow in the umbilical cord can be analysed to check whether the foetus is getting sufficient oxygen and nutrition.

Share article