The majority of young mothers and pregnant women know that it is possible to predict the possibility of chromosome and other aberrations with an ultrasound examination in early pregnancy. The practice so far indicates that women are still not familiar with the examination process itself in detail and that is why it is necessary to make a detailed description of the examination process so future parents could better understand the examination and participate in it actively.
The ultrasound examination between the 11th and 14th week of pregnancy is the basic screening test for detecting chromosome aberrations of the 21., 18. and 13. chromosome. Such examinations are performed in more than 40 countries around the world and it was first implemented in Slovenia in 1997.
Every human being has 46 chromosomes in his or her genetic code. Half of them are inherited from the mother and the other half from the father. Two of them are sex chromosomes x and y which determine the child’s sex during the insemination.
A chromosomal different fetus occurs when the number of chromosomes is changed. The most common chromosome aberrations arise when the number of chromosomes on one pair triples. That is how the so called trisomies arise – trisomy 21 (Down’s syndrome), trisomy 18 (Edwards’ syndrome) and trisomy 13 (Patau syndrome).
Ultrasound examinations between the 11th and 14th week of pregnancy for the assessment and prediction of risk of a chromosome aberration
The first practical instruction for a pregnant woman calling to make an appointment is to know the first day of her last period or to ask for the precise fetus size (vertex – coccyx length) measured by her gynaecologist at the first pregnancy examination. An average growth of the foetus is 2mm per day and the examination is best performed when the foetus is 45–84mm long from vertex to coccyx. The examination usually lasts 15 minutes and is not harmful for the pregnant woman or the fetus.
It is of a great importance that the gynaecologist performing the examination holds an international licence for measuring translucency scans and assessing the nasal bone. Our centre obtained the licence for translucency scans in 2005 and the licence for nasal bones in 2011. Conditions for obtaining the licence are very strict. Even more demanding is keeping the licence, since a gynaecologist must send all his/her annual examinations and results to the collection centre in London where all of them are evaluated. Only on the basis of a positive evaluation of all the examinations, may a renewal of the licence be issued (the list of the licensed doctors can be found on the website www.fetalmedicine.com).
A compound ultrasound examination with an examination of the hormones in the mother’s blood (double screen test)
The pregnant woman can decide on having a blood test during the ultrasound examination of her foetus. In the hormone laboratory, two specific pregnancy hormones are determined: free beta – HCG and pregnancy-associated plasma protein A PAPP-A. Thus, the value of risk assessment is enhanced from 90% to 93% with 5% of false positive test results.
Private gynecological and obstetrical clinic,
Damir Franić, MD, PhD. specialist in obstetrics and gynaecology.