Ultrasound is harmless to the fetus. Ultrasound has been used in pregnancy for over thirty years and numerous studies have shown the absence of harmful effects even in the long term on the fetus. For this reason, the diagnostic use of ultrasound is considered risk-free.

 

The examination is usually performed with a standard transabdominal approach and does not require any particular preparation for the pregnant woman. It is possible that in some cases the ultrasound examination requires the help of the transvaginal scan.

 

The ultrasound examination has limitations as it is unable to identify all the anomalies of the fetus and the structures connected to it. It is possible that the sensitivity of the ultrasound varies according to multiple factors, including:

 

• Indication: The degree of accuracy of a diagnostic examination is subject to the reason for which it is prescribed (fetal anatomy analysis, amniotic fluid evaluation, fetal growth, evaluation of blood flow through the umbilical cord)

• Gestational age of execution: at early gestational periods it becomes more difficult to identify malformations both due to the small size of the organs of the fetus and because some pathologies occur late during the course of gestation. On the other hand, the study of fetal anatomy during the third trimester is more complex as the increased size of the fetus makes the visualization of fetal structures more difficult.

• Factors limiting the examination: There are no fetal anomalies that are always and certainly detectable in the prenatal period, and therefore, due to the intrinsic limitations of the method, it is possible that some fetal anomalies, even serious, are not detected. The possibility of identifying an anomaly is not always related to its severity but depends on how much the ultrasound image is altered by it. Other factors that may affect the ability to view abnormalities are the position of the fetus in the uterus, the amount of amniotic fluid and the presence of limiting factors such as abdominal scarring, twins, and myomas. Finally, obesity or a thick abdominal wall tends to increase the acoustic impedance to ultrasound (the ease with which they cross the surfaces), significantly reducing the quality of the image.

 

For all these reasons, the normal outcome of a diagnostic ultrasound examination does not guarantee the birth of a child without any malformation.

 

Ultrasound diagnosis can be implemented with 3D and 4D techniques (which in addition to the three dimensions of space also includes time and therefore allows you to view fetal movements in real-time). This makes it easier to diagnose some malformations (especially on the face) and allows you to view anatomical planes that are normally not accessible (for example due to the momentary position of the fetus).

 

Sources and bibliography

 

Linee guida SIEOG 2015

Tratto da informative all'ecografia della SIEOG