Ultrasound (ultrasound) in its basis is usually based on 2 effects: the effect of reflection of ultrasonic waves from media with different densities and the Doppler effect . The ultrasonic wave is, first of all, a mechanical oscillation with a frequency of more than 20 thousand vibrations per second. At usual US - research the ultrasonic wave from the gauge of an emitter penetrates through fabrics of the person, is absorbed by them or is reflected.
Different tissues differently reflect ultrasound: air and bone almost completely reflect, and the more in the tissues of the fluid, the easier the wave passes. Through the liquid medium, the wave passes not only not weakening, but, conversely, with the amplification of the signal.
The reflected wave returns to the sensor and is converted into an electrical signal, and after processing it is displayed on the display screen in the form of a picture. Doplerography also uses ultrasonic waves, but reflected not from fixed surfaces, but from moving media. The essence of the method is that by reflecting from the object that is moving, the ultrasonic wave changes its frequency. The faster the speed of movement - the more noticeable, and therefore Doplerography is used to measure the flow rate of liquids through the vessels.
Is it harmful for pregnant women?
Since ultrasonic vibrations are mechanical, there is no need to speak about any harmful effects on the body of a pregnant or fetus. Yes, and modern sensors for a very short period of time emit a wave, and much more time catching its reflections (working in a pulsed mode). But with the continuous mode of ultrasound (especially in continuous Doppler systems), the signal is emitted long enough.
Ultrasound radiation has three mandatory effects, which should not be forgotten:
- mechanical (the effect of cavitation with the formation of cavities-ruptures in tissues, in which their damage at the micro level is possible);
- thermal (the absorbed energy of ultrasonic waves in tissues containing a large amount of liquid is converted into thermal, heating organs and tissues);
- physico-chemical (the rupture of intramolecular bonds under the influence of ultrasound, including at the level of DNA).
With prolonged exposure to ultrasound, especially in the continuous mode of radiation, any negative effects on the organs and tissues of the fetus are possible, because frequent ultrasound during pregnancy is harmful. Ultrasound examination can not be done too often, and dopplerography of the vessels of the placenta and fetus is strictly according to the indications.
How harmful is ultrasound in pregnancy?
Almost every pregnant woman, having learned that during pregnancy should undergo 3 screening ultrasound examinations, will think about whether ultrasound is harmful or not. Any impact on the body, including ultrasound, always has certain consequences. But if they are so insignificant that the benefit is much greater than the harm of ultrasound during pregnancy (the consequences may or may not occur), then it is worth considering, and for what do ultrasounds?
The examination is not intended only to find out the length of pregnancy or to establish the sex of the child - the second is usually of little interest to the doctor, and the first can be established by other methods of research. Ultrasound examination can reveal the pathology of pregnancy and the child itself, but not the one that can still be, but the one that already exists.
First of all, ultrasound confirms uterine pregnancy, helps diagnose an early pregnancy, major malformations of the fetus (for example, anencephaly of the fetus - lack of a brain), and other vices (lack of body parts, heart defects), in later terms shows the condition placenta and fetal presentation.
Whether it is harmful to do ultrasound often is another matter, but 3 screening examinations (at 11-14 weeks, at 18-21 weeks and at 30-32 weeks) must be passed necessarily in time to diagnose the severe pathology of pregnancy and the developmental defects of the fetus, in comparison with which the question that ultrasound is harmful in pregnancy, does not even arise.