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According to the current recommendations of the Polish Gynecological Society, 3 ultrasound examinations should be performed in a physiological pregnancy.
The first of them is carried out between the 11th and 14th week of pregnancy. During this examination, the number of gestational sacs, their location (inside or outside the uterus), the correct structure of the fetal egg – the presence of an embryo echo are assessed, and the normal heart function of the embryo is visualized. The location of the amniotic and chorionic villus is also checked, and in the case of multiple pregnancies – also their number.
The presence of the yolk sac is also confirmed by the 12th week of pregnancy. The CRL of the embryo is also measured – the parietal-sagittal length in the sagittal section. This dimension is the most reliable parameter for determining pregnancy size and due date.
Finally, the anatomy of the fetus is assessed. The structure of the skull and abdominal integuments are assessed – taking into account the physiological umbilical hernia lasting up to the 12th week of pregnancy. During this period, the fetal stomach looks like a single bubble. The heart of the fetus is checked – its location and frequency of action are assessed (bradycardia – below 90 beats per minute – indicates the risk of pregnancy). The urinary bladder should be centrally located in the lesser pelvis of the fetus. Attention is also paid to the presence and structure of the upper and lower limbs with the visualization of the hands and feet.
An important indicator in the early screening ultrasound examination for malformations is the assessment of the so-called nuchal translucency, that is, NT. It is a transient symptom and therefore it is important that the ultrasound is performed in the period when the measurement can be made, i.e. between 11th and 13th (+/- 6 days) weeks of pregnancy. Ultrasound examination with the assessment of nuchal translucency is difficult, requires appropriate equipment and skills of the doctor, as well as patience, because the fetus must be in the correct position (sagittal cross-section), with the head slightly bent. The NT dimension (measurement from the inner border of the skin to the inner border of the soft tissues of the fetal nape) is considered normal if it does not exceed 3 mm. The risk of chromosomal disorders increases with the increase in the size of NT, especially trisomy of chromosome 21 (Down syndrome), as well as trisomy of chromosomes 13 and 18.
An additional parameter taken into account when assessing the risk of congenital defects is the presence of a paired nasal bone. Its absence is an indication to look for more irregularities.
Finally, an ultrasound examines the umbilical cord. If it is three-vessel, then everything is fine. However, if he has only two blood vessels, the doctor is obliged to look for any further defects – mainly the heart.
In the case of pregnancy with an increased risk of congenital defects, i.e. primarily in pregnant women over 35, as well as in those who previously gave birth to a child with a genetic defect, or if one of the parents has chromosomal abnormalities (sometimes noticeable only at genetic test), additional diagnostics can be performed by determining certain biochemical parameters. At the beginning of pregnancy (first trimester), the so-called test DAD, the essence of which is to determine the level of certain proteins secreted by the placenta, including beta HCG in the blood.
In later pregnancy, i.e. in the second trimester, another test is performed – triple test. This test includes blood levels of beta HCG, alpha-fetoprotein and estriol. Based on the results of these tests and the ultrasound performed on the same day, the risk of genetic defects in the child is calculated. If it is elevated, the patient is qualified for further tests in specialist centers, where the so-called amniocentesis, i.e. puncture of the amniotic sac to collect amniotic fluid containing fetal cells for the determination of fetal karyotype. Then it becomes clear whether the fetus is healthy or sick. You can also perform the procedure chorionic villus samplingwhich involves puncturing the chorion tissue between 8 and 10 weeks of pregnancy.
It is customary to adopt a pregnant woman over 35 years of age abroad. It turns out, however, that a significant number of children with Down syndrome are born from pregnancies before the age of 35. Therefore, it seems logical that – in accordance with the recommendations of the Polish Geological Society – each patient between the 11th and 13th week of pregnancy should be informed about the possibility of testing for genetic defects.
Text: lek. med. Ewa Zarudzka
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