Control of the fetus is required during pregnancy to check that everything is developing normally. Ultrasound is the only method to monitor the evolution of the embryo and its use has become widespread due to its convenience and speed of diagnosis. In addition, its reliability and the fact that it does not represent any risk to the mother or the child have made pregnant women eliminate part of their fears during the nine months of gestation.

An ultrasound is a diagnostic imaging that works through ultrasound . These are produced in the ultrasound probe (the transducer), are emitted on the mother’s body, bounce off the fetus and are integrated by the device, producing an image that shows a gray scale and shapes.

The first ultrasounds were done about 25 years ago, but the technique has become widespread in the last decade. During this time, the development of the devices has been spectacular and progress continues in their modernization. An ultrasound system is made up of the following elements: a probe or transducer , a screen, video equipment and a processing device.

When should ultrasounds be done?

– First ultrasound . The first ultrasound is done around the sixth to ninth week of pregnancy. At this time, the embryos measure about 10 millimeters and the test will allow: confirm the pregnancy, check if the pregnancy is well located within the fetus, see the number of embryos there are (if it is a single fetus or if it is a a multiple pregnancy), examine that the embryos are alive and have a heartbeat, see the size of the embryos and if this coincides with the date of the woman’s last menstruation (this serves to correctly date the gestation, diagnose the pregnancy as an evolutionary pregnancy, establish the date of the following controls and calculate a probable date of delivery).

– Second ultrasound . The second ultrasound is taken between weeks 11 and 14 . At this time, the fetus measures about 6 or 7 centimeters and the ultrasound will be used to make a general assessment of its condition (limbs, extremities, heart and abdomen).

– Third ultrasound . The third ultrasound is done around weeks 20 and 22 . At this time, the fetus is more formed and larger, so it must be measured in parts: skull-buttock length, which is usually about 10 millimeters; head length; abdominal circumference; biparietal or head diameter; length of the femur. When the fetus is small, its size can be known more precisely, but when measuring it in parts there is a margin of error between 15 and 20 percent.

– Fourth ultrasound . The fourth ultrasound is usually done between 33 and 35 weeks . The fetus is measured in parts, following the same process as in the third ultrasound, and the fetal morphology, the amount of fluid and the fetal growth are checked. If it is a risk pregnancy, the number of ultrasounds performed will depend on the type of pathology. For example, multiple pregnancies or fetuses that grow less than usual should be more closely monitored by the specialist. It is important to clarify that ultrasound can only discover fetal malformations that may have a morphological translation, that is, that show an altered image. Therefore, a mental retardation cannot be diagnosed that is not accompanied by any cerebral alteration nor the dysfunctions of an organ. For example, you cannot see if the liver is malfunctioning, but you can see if there is some type of cyst.

Types of ultrasound

Depending on the route used, there are two types of ultrasound: the transvaginal route is reserved for the first weeks of pregnancy (the first and second ultrasound), while the abdominal ones are used from the second trimester. This is because the resolution of abdominal ultrasound is better when the fetus is larger, whereas transvaginal ultrasound only offers a clear image when it is small.

In addition, there are three ultrasound techniques . Conventional ultrasound is two-dimensional , which is currently the basis for all prenatal and malformation diagnoses. Recently, 3D and 4D ultrasound has been incorporated . The 3D shows the fetus with volume, while the 4D adds movement. Until now, traditional ultrasounds showed a photograph, therefore, a static image.

The effectiveness of 3D and 4D ultrasounds has yet to be demonstrated, although experts point out that it is a good method to complement two-dimensional tests and that they may even exceed them in their use.

3D and 4D ultrasounds

In 1993, 3D and 4D ultrasound appeared as a result of the spectacular advance in ultrasound technology. From that moment we can talk about the development of ultrasound machines that give a high quality image with greater ease at the time of being performed. Despite the extraordinary progress, it was not until 2003 that it began to be practically carried out on an experimental basis in very few centers in Spain. Since then, its use has become widespread thanks to the appearance of ultrasound machines that are easier to handle and with higher visual quality.

3D ultrasound consists of the three – dimensional visualization of the structures to be studied, such as the baby’s organs, in a static way. 4D ultrasound is the same, but in real time. It allows the structures to be studied dynamically, being able to see, for example, fetal movements.

Its use is more and more frequent but not all centers have ultrasound scanners, since their acquisition cost is still very high. Currently they are not performed systematically in public hospitals because not all have ultrasound scanners and because ultrasound scans are not performed on demand of patients, but rather those that are indicated by protocol.

Its main attraction, especially for parents, lies in the degree of realism. Although we strive to decipher the structure of our son in the results of 2D ultrasound, it is not always easy for the layman and, in this sense, three and four dimensional ultrasound are clear and easy to interpret. The images obtained, mainly in 4D echo, allow to see spectacular images of the face and fetal limbs in movement. Images of the fetus smiling, sticking out the tongue, making facial expressions are even appreciated … a value that makes them a highly demanded examination by patients.

They allow the best external visualization of the fetus and, therefore, of the anomalies that have usually already been diagnosed by 2D ultrasound. They provide more information than 2D ultrasound in some specific cases, although diagnoses are still made in most cases by 2D ultrasound. In gynecology, they allow a better visualization of uterine malformations that is not achieved with 2D ultrasound, as well as the possibility of studying the three-dimensional vascularization of tumors.

Despite its multiple benefits, parents should be aware of its limitations in the diagnosis of fetal malformations , since in most cases its detection power does not exceed that of 2D ultrasound, which is 60-65%. The main function of all ultrasound is to detect problems in the baby’s organs and, despite the progress they represent, neither 3D nor 4D allows better visualization of internal fetal alterations, such as metabolic problems. What is detected are alterations of the central nervous system thanks to the high quality of the image.