The Istenhegyi Genetic Diagnostic Centre uses Medison four-dimensional ultrasonic equipment. Sonography is carried out by our experienced gynecologist-obstetricians, who have been accredited by FMF (Fetal Medicine Foundation), one of the leading organizations in ultrasonography. FMF inspects scans made by their accredited sonographers every six months. Scans are captured on DVD and in printed pictures.
- 6-8 weeks: Confirmation of pregnancy, screening for ectopic pregnancy
- 11-13 weeks: Dating: establishment of the gestational age; first genetic screening (Combined screening)
- 18-20 weeks: Second genetic screening, 4D image
- 30 and 39 weeks: General ultrasonography, 4D image
Pregnancy is confirmed at an early stage with the ultrasound scan done after the woman skips a menstrual period. The scan determines whether it is a single or multiple pregnancy, and exclude the possibility of ectopic pregnancy.
It is important to determine the gestational age, which is calculated from the first day of the last menstrual period. However, a lot of women have irregular periods that may differ significantly from the classic 28-day intervals, or the woman may not remember when exactly she had the first day of her last period. In such cases we have to rely on ultrasonography. The gestation age is easiest to calculate from the crown-rump length marked CRL on the diagnostic sheet. At 11 weeks CRL is about 40 mm, at 12 weeks it is 55 mm, at 13 weeks it is 65-70 mm. A table is used to calculate the gestational age, which is recorded on the diagnostic sheet by Grav.s. Gestational age is sometimes mixed with fetal age (also known as conception age or fertilization age). Gestation age is two weeks more than fetal age, so if the exact time of conception is known (IVF, vaginal thermometer, definite time of coitus, etc.), two weeks must be added.
At the first trimester (the first third of the pregnancy) ultrasonographic genetic screening nuchal translucency is measured. This is entered on the diagnostic sheet as NT or nucha. NT should be measured at 11-13 weeks. The nucha, or nuchal fold, is a fold at the back of the neck of the fetus. If the fluid under the skin in the nuchal area is excessive, the scan will show edema and the NT measurement will be high. This could be indicative of certain defects (Down’s syndrome, other genetic defects or heart problems). NT is generally considered normal up to 3 mm, but the measured value depends on a number of factors. One is that the nuchal fold thickness grows with the fetus, so measurements taken at 11, 12 or 13 weeks will obviously be different. Human and other factors must also be taken into consideration, for instance the type of equipment and the experience of the sonographer. Measurements taken by different professionals can be consistently different, so the result must be checked against the average of the sonographer or ob-gyn specialist. The resolution of the scan may be different: the higher the resolution the more accurate the diagnosis. Unfortunately sophisticated, high-resolution ultrasound equipment is very expensive and many institutions cannot afford them. Also, the fetus must be in a neutral position for the NT scan because if its head is bent forward or backward the NT value will be lower or higher that in reality.
Nasal bone scan
The British general practitioner John Langdon Down observed as early as in 1866 that people with Down’s syndrome tended to have a smaller nose. The question is, can this be detected with ultrasonography? There is evidence that in Down’s syndrome development of the nasal bone starts later, so it is generally not visible in the first trimester scan. The presence of the nasal bone is a significant step towards eliminating the risk of Down’s syndrome, thus several antenatal centres have started nasal bone scan. The nasal bone is not measured at the first trimester scan, only its presence or absence is established. The nasal bone is indicated by NB on the diagnostic sheet. The first trimester scan may also include other biometric data of the embryo: BPD (biparietal diameter or the diameter of the head), HC (head circumference), AD (abdominal diameter), AC (abdominal circumference), FL (femur length).
The second trimester ultrasonic scan takes place in the second third of the pregnancy, in 18-20 weeks. Measurements can be similar to those taken at the first trimester scan except for CRL and NT, which are not tested at this stage. As the result of the AFP test is available at this stage open neural tube defects and cranial developmental disorders are screened besides taking measurements. A high-quality ultrasonograph can detect open neural tube defects in 95% of the cases, and fetal acrania in 100% of the cases. These abnormalities are indicated by high AFP level. The risk of open neural tube defects can be greatly reduced if the mother takes fetal protective products that contain folic acid at the early stage of pregnancy (Family planning). At 18-20 weeks the development of bones and internal organs is scanned. Special attention is paid to the fetal heart as developmental problems of the heart can indicate genetic abnormalities. Nasal bone length is measured at this stage as an additional method of screening for Down’s syndrome. At this stage of the pregnancy the nasal bone should exceed 2.5 mm, its average length is 4-5 mm.
If all is found in order at the first and second trimester screenings and the mother has no complaints, the fetus is routinely checked ultrasonically at 30 and 39 weeks. The scans monitor the position and development of the fetus; genetic abnormalities are not screened at this stage.