First trimester screening is a prenatal study that is performed from 11 to 14 weeks of gestation, visualizes the uterus, ovaries, fallopian tubes, corpus luteum, chorion, yolk sac, amniotic fluid and embryo. It allows you to diagnose the threat of spontaneous abortion, bladder drift, gross fetal pathologies, chromosomal diseases. It is indicated for single and multiple pregnancies, performed in two-dimensional mode through transvaginal and transabdominal access.
Preparation
Ultrasound screening of the 1st trimester, carried out using the transvaginal method, does not require special training. Transabdominal examination gives a clearer result when the bladder is filled, therefore, in 30 minutes it is necessary to drink 0.5-0.7 liters of pure still water and not visit the toilet until the end of the procedure.
What shows
For first trimester screening, 2D mode is used. At an early stage, the most informative is a two-dimensional black-and-white image. More complex studies are conducted after 20-22 weeks of gestation. Normally, at 11-14 weeks, ultrasound visualizes one fetal egg in the upper part of the uterine cavity if the pregnancy is singleton; two or more fetal eggs when the pregnancy is multiple.
The results of ultrasound of the first trimester reflect the anatomical features of the fetus: CPS (coccygeal-parietal size), HC (head circumference), BHS (biparietal head size), TCS (thickness of the collar space), thickness of the nasal bone, structure of the brain, heart, limb bones and skull, heart rate, localization and size of the chorion, volume of amniotic fluid, uterine tone. The study makes it possible to identify such pathologies as:
- Frozen pregnancy. An undeveloped pregnancy is indicated by a decrease in the anatomical parameters of the fetus, pathology of the development of the body stem and umbilical cord, the absence of a fetus and / or yolk sac in the fetal egg, the presence of amorphous tissue masses in it. Transvaginal echography reveals the absence of a heartbeat (with a CPS scan of more than 6 mm).
- The threat of miscarriage. The most common echo sign of the threat of termination of pregnancy is a local thickening of the uterine walls, indicating hypertonicity of the myometrium. There may be one or more areas of increased tone. The fetal egg has an irregular deformed shape. The risk of embryo detachment is high with the formation of a hypertonus site at the placenta formation site.
- Pathology of the chorion. The pathologies of the chorion include its presentation and hypoplasia, as well as molar pregnancy. Chorionic hypoplasia is revealed as a decrease in its size, the absence of clearly visualized villi. When the chorion is presented, its low location and complete or partial overlap of the inner pharynx are visualized. With a bubble drift, the uterus is enlarged, heterogeneous contents are found in its cavity – a picture of a “snow storm” (pathologically large villi).
- Fetal developmental disorders. Ultrasound in the 1st trimester reveals gross abnormalities of fetal development: absence of limbs and brain (anencephaly), a two-chamber heart, defects of the anterior abdominal wall with prolapse of internal organs and intestinal loops, diaphragmatic hernias of the stomach, deformation of the skull bones, asymmetry of the cerebral hemispheres.
- Genetic diseases of the fetus. In the first trimester, the risk of the most common genetic diseases is determined: Down syndrome, Patau syndrome, Edwards syndrome, Cornelia de Lange syndrome, triploidy. The main ultrasound signs are an increase in the TCS index, the absence or deformation of the nasal bone, multiple anomalies of the formation of organs.
Advantages
First trimester screening is an informative and safe diagnostic method that allows timely detection of pregnancy pathologies, primary diagnosis of severe fetal pathologies and determination of the feasibility of invasive research methods. The disadvantage of the technique is unsatisfactory visualization in the presence of uterine hypertension, excess weight or edema in a pregnant woman. Two-dimensional ultrasound used during the first screening has the lowest cost in comparison with three-dimensional and four-dimensional echography, complex ultrasound with ultrasound, CCG and fetal echocardiography used at a later date.
