Nuchal translucency
Obstetrics
GYNECOLOGIST
assist. prof. Damir Franić MD PhD, Specialist in Gynecology and Obstetrics
GYNECOLOGIST
Maja Franić Ivanišević MD PhD, Specialist in Gynecology and Obstetrics
Why undergo an examination?
Trisomy of chromosome 21, or Down syndrome, is the most common chromosomal abnormality in newborns. This abnormality occurs in every 500 to 600 births. Down syndrome was first mentioned by the English physician John Langdon Down in 1866 when he described individuals who differed from others due to their distinct appearance and intellectual disability. He observed features like a short neck with excess skin folds, a flattened face with a small nose and narrow eye openings, and an overly rounded head. More than one-third of such children are also born with a congenital heart defect.
The majority of young mothers and pregnant women are aware that early pregnancy ultrasound examinations can predict the possibility of chromosomal and other fetal abnormalities. However, many are not well-informed about the actual process of the examination. Therefore, it is necessary to provide a detailed description of the examination procedure to help expectant parents better understand the test and actively participate in it.
An ultrasound examination performed between the 11th and 14th week of pregnancy is the basic screening test for detecting chromosomal abnormalities of chromosomes 21, 18, and 13. Such screenings are conducted in more than 40 countries around the world, and they were introduced in Slovenia in 1997.
Chromosomal Abnormalities
Every human being has 46 chromosomes in their genetic makeup, with half of them inherited from the mother and the other half from the father. Two of these chromosomes are the sex chromosomes, X and Y, which determine the sex of the child at conception.
Chromosomal abnormalities occur when there is a change in the number of chromosomes. The most common chromosomal abnormalities result from a triplication of a single pair of chromosomes, leading to conditions known as trisomies. Trisomies include trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome).
Ultrasonographic examination between the 11th and 14th weeks of pregnancy for assessing and predicting the risk of chromosomal abnormalities
The first practical advice for a pregnant woman scheduling an appointment by phone is to know the first day of her last menstrual period or to request the precise measurement of the crown-rump length by her gynecologist during the first pregnancy check-up. The average fetal growth is 2 mm per day, and it is best to have the examination when the fetus measures between 45-84 mm from crown to rump. The examination typically lasts around 15 minutes and is not dangerous for the pregnant woman or the fetus.
It is crucial that the gynecologist performing the examination has an international license for measuring nuchal translucency and assessing the nasal bone. Our center obtained the license for nuchal translucency in 2005 and for the nasal bone in 2011. The requirements for obtaining this license are very strict. Even more demanding is the maintenance of the license, as the gynecologist must send all their annual examinations and results to a central center in London, where they are all evaluated. Only with positively evaluated examinations can the license be extended (you can find a list of licensed doctors at www.fetalmedicine.com).
How does the examination proceed?
The pregnant woman should have an empty bladder during the examination. The examination begins by determining the number of fetuses and detecting fetal heartbeats. We measure the precise length from the fetal crown to rump, which allows us to estimate the expected due date, which is not changed later (see Figure 1).
We then assess the early development of the fetus, measure the size and shape of the fetal head, and examine the future brain structures (see Figure 2). We cannot yet evaluate the spine with the spinal cord, but we can already identify major irregularities.
In the chest, we determine the position of the heart and measure the heart rate per minute, as some chromosomal abnormalities are also associated with the number of heartbeats.
In the abdomen, we locate the stomach, and below it, we carefully examine whether the entry point of the umbilical cord into the abdomen is closed (see Figure 3). An open abdominal wall is usually a sign of chromosomal abnormalities in the 18th and 13th chromosomes or triploidy. When examining the lower part of the abdomen, we find the fetal bladder, which should not be larger than 6 mm (see Figure 4). With the appropriate size of the bladder and the amount of amniotic fluid around the fetus, we can conclude that the excretory system has developed correctly. We also examine the fetal arms and legs and count the fingers.
This is followed by the examination of the presence of the nasal bone, which was introduced into the program in 2004 and represents one of the main innovations for calculating the risk (see Figure 5). The absence of the nasal bone indicates an increased risk of Down’s syndrome because 60% of fetuses with Down’s syndrome and other chromosomal abnormalities do not have a developed and visible nasal bone. If the fetus is in the sagittal position (on its back or on its belly), the nuchal translucency is measured at least three times (see Figure 6). The highest value is used to calculate the risk, which should not exceed 2.5 mm. A value greater than 3.5 mm significantly increases the chance of heart abnormalities. The prediction of the risk of chromosomal abnormalities in the fetus is calculated based on the mother’s age, the thickness of the nuchal translucency, the assessment of the presence of the nasal bone, and the measurement of fetal length (45 – 84 mm). The reliability of the prediction is 90%, with a 5% false-positive rate. A risk greater than 1:300 represents a threshold indicating a high risk and requires further testing and karyotyping of the fetus (early amniocentesis or chorionic villus sampling).
A comprehensive ultrasound examination combined with the measurement of pregnancy hormones in the mother's blood (double hormonal test) is performed.
At the same time as the fetal ultrasound examination, the pregnant woman can choose to have her blood drawn. In the hormonal laboratory, two specific pregnancy hormones are determined: free beta-human chorionic gonadotropin (free beta-HCG) and pregnancy-associated plasma protein A (PAPP-A). This increases the risk assessment’s accuracy from 90% to 93% with a 5% false-positive rate.
Conclusion
Ultrasonographic examination between the 11th and 14th weeks of pregnancy represents a fundamental screening test for detecting chromosomal abnormalities. It is entirely safe for both the pregnant woman and the fetus. During this examination, we determine the estimated due date, evaluate the fetus, and based on the results of the nuchal translucency measurement, assess the risk of giving birth to a child with chromosomal abnormalities (trisomy 13, 18, and 21). This examination allows us to detect 90% of chromosomally different fetuses, and when combined with a hormonal test, the result increases to 93%, with a possible 5% margin of error. If the results indicate a high risk, we recommend fetal karyotyping using the method of early amniocentesis or chorionic villus sampling.
Office hours of the clinic
MONDAY 13:00 - 20:00
TUESDAY 08:00 - 15:00
WEDESDAY 8:00 - 15:00
THURSDAY 8:00 - 15:00
FRIDAY 8:00 - 15:00
Appointment scheduling
- PHONE APPOINTMENTS (tel: 03 5 815 550) Afternoons from 3:00 PM to 7:00 PM, mornings from 8:00 AM to 12:00 PM.
- EMAIL APPOINTMENTS: ginekologija.drfranic@siol.net
- MAIL APPOINTMENTS: Private Gynecology and Obstetrics Clinic, Celjska cesta 7, 3250 Rogaška Slatina, Slovenia
- IN-PERSON APPOINTMENTS
The responsible person for scheduling is sr. Hedvika Verbajs
BONE DENSITY MEASUREMENT (DXA) CLINIC only by prior appointment.
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