Northwestern Prenatal Genetic Centre
Training Centre of Ott's Institute of Obstetrics & Gynecology RAMS
14-th Liniya Vasilyevskogo ostrova, 7
+7 (812) 677-14-08, 921-26-32, 921-26-37
Usual 2D scan is a series of two-dimensional plane images of the fetus or its individual organs.
Three-dimensional (3D) scan is a method for producing an image that is achieved through a complex transformation of the resulting two-dimensional information into three-dimensional volumetric model. Conversions are performed by a special three-dimensional transducer and computer programs included in the ultrasonic machine. The obtained volumes can be rotated and viewed from different angles.
Four-dimensional (4D) scan is getting three-dimensional image of the fetus and its movements in real time. Thus, in addition to three-dimensional image of the fetus a fourth dimension – time – is used, and motor activity and facial expressions of the fetus in motion can be considered.
3D/4D ultrasound can be done at different stages of pregnancy, but the result and the image quality is primarily dependent on the position of the fetus in the uterus, the amount of amniotic fluid in front of baby’s face, the obstacles to ultrasonic wave (uterine fibroids, scar on the uterus, subcutaneous tissue can influent the study and degrade image quality). For example, if the fetus is close to the uterine wall, then it is practically impossible to get a three-dimensional image of its face, as it is impossible to see the face of a man who rested his head against the wall. Sometimes you have to wait 15-20 minutes, and continue to study after the change of the fetus position.
The best period for a facial image of the fetus is 20-26 weeks of pregnancy. During those dates a fetus often changes its position, and there is enough fluid to see the face. After 30 weeks of pregnancy the fetus is so big that it has to group well to fit in the uterus. That’s why obtaining a beautiful three-dimensional image of the face may be difficult or even impossible after 30 weeks of pregnancy - all depends on the position of the fetus.
It is important to understand that 3D/4D ultrasound is performed in addition to the usual ultrasound of the fetus, and cannot fully replace it. Measuring the size of the fetus and the exclusion of abnormalities are performed using two-dimensional ultrasound. Only in case of few diseases 3D scan can give the doctor some additional information.