Second trimester screening test is a planned study that is performed at a period of 20-22 weeks, displays the structure and position of the placenta, umbilical cord, cervix, fetal size, structure and functioning of its internal organs. It allows you to diagnose the risk of termination of pregnancy, developmental delay and anatomical abnormalities of the fetus, fetoplacental insufficiency, umbilical cord pathology. The procedure is performed for multiple and single pregnancies in 2D mode.
Second trimester screening test is performed through transabdominal access, no special training is required.
Standard second trimester screening test is a study in 2D mode. The size of the fetus, the structure of organs and bones, the formation of the placenta, the location and structure of the umbilical cord, the amount of amniotic fluid is determined. If necessary, ultrasound in three-dimensional and four-dimensional mode, Dopplerography and echo cardiography of the fetus are additionally prescribed. During the screening examination in the 2nd trimester , the following pathologies may be identified:
- Incorrect presentation of the fetus. Incorrect presentation of the fetus is considered to be pelvic (buttocks or legs down), oblique and transverse (with a deviation of the fetal axis passing through the back of the head and buttocks from the longitudinal axis of the uterus). Up to 30-32 weeks, incorrect, that is, non-head presentation is assessed as a situation requiring observation, since the child can turn around to the correct position or stay the same.
- Abnormalities of fetal development. In the second trimester, it is possible to accurately determine the structure of organs and body parts, to identify disorders of fetal development that are invisible at the first screening. Shortening or elongation of the femur and humerus, reduction or increase in the circumference of the head, abnormalities of the structure of the fingers, expansion of the cerebral ventricles, accumulation of cerebral fluid in the cranial cavity, absence of a cardiac septum, dilation of the renal pelvis and other abnormalities can be detected.
- Fetal development delay. The symmetrical form of intrauterine fetal growth retardation on ultrasound manifests itself as a proportional lag in body weight and fetal length, most fetometry indicators are lower than normal, do not fit into the framework of individual fluctuations. With an asymmetric form, the development of the fetus is disproportionate: the fetal body weight is insufficient, and the length corresponds to the norm; the development of the chest and abdominal organs lags behind, the volume of subcutaneous fat is reduced, and the volume of the head and the length of the limbs correspond to the term.
- Fetoplacental insufficiency. Direct signs of acute fetoplacental insufficiency are premature detachment of the normally located placenta, a sharp violation of the uteroplacental blood flow. In the chronic form of pathology, the speed and intensity of blood circulation is reduced, the thickness of the placenta is less than the norm by 5 mm or more. Indirect signs of AFN are hypoxia and impaired fetal cardiac activity, delayed development and decreased motor activity, abnormal amount of amniotic fluid (more often – lack of water), calcifications in the placenta.
- Pathology of the umbilical cord. Pathologies of the umbilical cord at this time include its marginal, split or shell attachment, as well as the presence of only one feeding artery instead of two. These disorders are associated with the risk of fetal hypoxia, the development of heart disease and disorders of cardiovascular activity.
Ultrasound screening is part of a comprehensive planned examination of pregnant women, which also includes an examination by a gynecologist and a biochemical blood test. The diagnosis is made based on a comparison of data from all studies.
During pregnancy, ultrasound diagnostics remains the only imaging method that is safe for the expectant mother and child. The study has no contraindications, if necessary, it can be used repeatedly. The cost of standard two-dimensional sonography is cheaper than the price of additional studies – three-dimensional and four-dimensional ultrasound, dopplerography of uteroplacental vessels, fetal echocardiography. The disadvantage of ultrasound screening is unsatisfactory visualization with edema and excess weight in a pregnant woman, hypertonicity of the uterus, non-standard location of the fetus.