The patient should have a filled but not overgrown bladder, so that the lower uterine segment and the vagina are visualized distinctly. Ask the patient to drink 3 or 4 glasses of water before testing.
To study the placenta it is necessary to make multiple longitudinal and transverse sections. You may also need slanting slices.
At the 16th week of pregnancy, the placenta occupies half of the inner surface of the uterus. In terms of 36-40 weeks, the placenta takes from 1/4 to 1/3 of the area of the inner surface of the uterus.
Reduction of the uterus can simulate the placenta or formation in the wall of the uterus. Repeat the test after 5 minutes, however keep in mind that the contraction can last a longer time. If in doubt, wait for a while.
Precise determination of the location of the placenta is very important for patients with vaginal bleeding or in the presence of signs of fetal trouble, especially in late pregnancy.
Overgrowth of the bladder can sometimes create a false echographic pattern of placenta previa. Ask the patient to partially empty the bladder and repeat the test.
Location of the placenta
The placenta is easily visualized starting from the 14th week of pregnancy. To examine the placenta located on the back wall, it is necessary to make slanting slices.
The location of the placenta is assessed in relation to the wall of the uterus and the axis of the cervical canal. The position of the placenta can be as follows: along the middle line, on the right side wall, on the left side wall. Also, the placenta can be located on the front wall, on the front wall with spreading to the bottom. In the field of the bottom, on the back wall, on the rear wall with the transition to the bottom.
It is extremely important to visualize the cervical canal when suspicion of placenta previa. The cervical canal is visualized as an echogenic line surrounded by two hypo- or anechogenous rims, or it can be entirely hypoechoic. The cervix and lower uterine segment will be visualized differently, depending on the degree of filling of the bladder. With a full bladder, the cervix appears elongated; side shadows from the head of the fetus, bladder or pelvic bones can hide some details. With a smaller filling of the bladder, the cervix changes its orientation to a more vertical one and becomes perpendicular to the scanning plane. The cervix is more difficult to visualize with an empty bladder, but under these conditions it is less biased, and the relationship between the placenta and the cervical canal is more clearly defined.
The diagnosis of placenta previa, established during the study with a complete bladder, should be confirmed in the study after its partial emptying.
Location of the placenta
- If the placenta completely covers the inner uterine ooze, then this is the central placenta previa.
- If the edge of the placenta overlaps the internal uterine sores, there is a marginal presentation of the placenta (internal uterine pharynx is still completely covered by the placental tissue).
- If the lower edge of the placenta is located close to the internal uterine throat, there is a low attachment of the placenta. Precisely to establish such a diagnosis is difficult, since only part of the uterine throat is covered with the placenta.
The location of the placenta may change during pregnancy. If the study is performed with a filled bladder, repeat the study with a partially empty bladder.
Preposition of the placenta may be determined in the early stages of pregnancy and not determined at the end. However, the central placenta previa is diagnosed at any time of pregnancy, marginal placenta previa - after 30 weeks, and after that no significant changes are noted. If bleeding is not observed in the second trimester of pregnancy, the second standard ultrasound examination of the placenta can be postponed until 36 weeks of gestation to confirm the diagnosis of presentation. If there is any doubt, the test should be repeated before the 38th week of pregnancy or immediately before childbirth.
Normal echostructure of the placenta
The placenta may be uniform or have isoechogenic or hyperechogenic foci along the basal layer. At the last stages of pregnancy, echogenic septa can be determined throughout the thickness of the placenta.
Anechogenous areas immediately below the chorionic plate or within the placenta are often detected as a result of thrombosis and subsequent fibrin accumulation. If they are not extensive, they can be considered normal.
Intraplacental anechogenous areas can be caused by the blood flow seen in the enlarged veins. If they affect only a small part of the placenta, they have no clinical significance.
Under the basal layer of the placenta, it is possible to see the retroplacental hypoechoic canals along the uterine wall as a result of venous outflow. They should not be confused with retroplacental hematoma.
Pathology of the placenta
A bubble drift can easily be diagnosed by the inherent echographic sign of a "snow storm". It should be noted that the fetus may still be alive if the process affects only part of the placenta.
Enlargement (thickening) of the placenta
Measurement of the thickness of the placenta is too inaccurate, in order to significantly affect the process of diagnosis. Any evaluation is rather subjective.
- Thickening of the placenta occurs with Rh-conflict or fecal edema.
- Diffuse thickening of the placenta can be observed in mild forms of diabetes maternal.
- The placenta may thicken if the mother has had an infectious disease during pregnancy.
- The placenta can be thickened by placental abruption.
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Thinning of the placenta
- The placenta is usually thinned if the mother has insulin-dependent diabetes.
- The placenta can be thinner! Ia if the mother has a pre-eclampsia or intrauterine growth retardation.
Echography is not a very sensitive method for diagnosing placental abruption. The detachment is characterized by the presence of hypo- or anechogenous areas under the placenta or raising the edge of the placenta. Blood can sometimes exfoliate the placenta.
The hematoma can look hyperechoic, and sometimes by echogenicity it is comparable to a normal placenta. In this case, the only sign of a hematoma may be a local thickening of the placenta, but the placenta may look completely unchanged.
Ultrasound is not a very accurate method for diagnosing placental abruption. Clinical research is still extremely important.