An obstetric ultrasound is a diagnostic method that uses ultrasound to diagnose whether or not a pregnancy exists, as well as to assess the condition of the embryo or fetus.
It is a test that causes no harm to the fetus or the mother, since it does not use ionizing radiation.
Thus, obstetric ultrasound provides the following indications:
- Establishes whether a pregnancy exists
- Determines whether it is a single or multiple pregnancy.
- Estimates an exact gestational time
- Discover and diagnose if there are congenital lesions or malformations.
- Assesses the position and weight of the fetus
- Examines the position of the placenta and the amount of amniotic fluid.
How is obstetric ultrasound performed?
During the first trimester of gestation, ultrasound is performed vaginally, as this provides a clearer image.
However, after the 14th week, the abdominal route is usually chosen, unless the cervical length or the position of the placenta is to be assessed.
How many ultrasounds are performed per pregnancy?
The final number of ultrasounds performed varies according to each pregnancy, but it is usually recommended to perform at least four ultrasounds:
- Pregnancy confirmation ultrasound, at around 6 to 8 weeks.
- First trimester ultrasound (11+6 or 13+6 weeks)
- Second trimester ultrasound, between the 20th or 22nd week.
- Third trimester ultrasound at 28 or 37 weeks.
Differences and function of 3D and 4D ultrasounds
Three-dimensional (3D) ultrasound is an ultrasound that represents in three dimensions the space of the images obtained through conventional two-dimensional ultrasound.
On the other hand, 4D ultrasound is a technique that makes it possible to visualize the fetus in three dimensions and in motion in real time. Thanks to this technique it is possible to visualize the fetus moving inside the mother’s uterus. At the same time, in some moments the images can offer very realistic quality details, and it is even possible to observe how the fetus is behaving inside the uterus: a smile, a grimace, a yawn….
However, it is worth mentioning that although the purpose of this test is recreational, it allows the identification of some fetal pathologies -such as cleft lip- providing information on the malformation.
The 4D ultrasound can be performed at any time during pregnancy, although between weeks 27 and 32 is the ideal time to observe the baby’s facial features with the greatest possible definition.
The technique has some limitations, and the final result varies depending on the amount of amniotic fluid present, the position of the placenta or the position of the fetus itself.
Prenatal diagnosis, a tool for detecting congenital anomalies
In recent years there have been advances in the field of prenatal diagnosis that have made it possible to make an early diagnosis of a high percentage of so-called congenital anomalies.
First of all, a distinction must be made between a chromosomal alteration and a genetic alteration.
An alteration in the chromosomes of the fetus indicates the existence of a lack, an excess or an alteration in a chromosome of the fetus. All people have 23 pairs of chromosomes in their cells, one coming from the egg and one from the male sperm.
Thus, each chromosome is composed of thousands of genes, although not all of them can be identified. An example would be Down syndrome, which is a chromosomal alteration in which there are three chromosomes instead of two in the pair of chromosomes 21. However, a disease such as cystic fibrosis, which is a genetic alteration, i.e. the gene inside the chromosome, is impossible to diagnose.
Invasive prenatal diagnostic techniques have made it possible to know the genetic map thanks to the extraction of samples with various techniques. These are the following:
- Chorion biopsy
- Genetic amniocentesis
- Cordocentesis or funiculocentesis
However, in the activity we have the so-called non-invasive prenatal test, which can identify the diagnosis of many chromosomal and genetic diseases.
This test, although in many cases it is not covered by medical insurance companies, does not entail any risk for the mother, since it is performed with a single analysis of the mother.
For more information on ultrasounds and their results, contact a specialist in Gynecology.