In obstetrics, there are many indices, thanks to which you can determine the duration of gestation, the presence or absence of abnormalities in the development of the fetus. The biparietal size of the fetal head is one of those indices, it is more accurate than others to tell about the term of pregnancy. The biparietal size of the fetal head can be determined with the help of ultrasound examination, and its informativeness in the period from 12 to 28 weeks is especially high. In this article we will consider how to measure the biparietal size of the head, what its indices are at different developmental dates of the fetus and its possible deviations from the norm.
The biparietal size of the fetal head is normal
BDP of the fetal head is the distance between the outer and inner contours of both parietal bones, the line connecting the outer contours of the parietal bones should pass over the thalamus. Deviation from the rules of measurement leads to a distortion of the results and, as a consequence, not to the correct determination of the gestational age. Each pregnancy corresponds to a certain value of the fetal BPR in the norm. As the gestation period increases, the biparietal size of the fetal head increases, and at the end of the pregnancy its growth rate decreases markedly. For example, the BDP of the fetus at 12 weeks, on average, is 21 mm, the BDP of the fetus at 13 weeks is 24 mm, at 16 weeks - 34 mm, at 24 weeks - 61 mm, the BPR at 32 weeks is 82 mm, at 38 weeks - 84 mm, and in 40 weeks - 96 mm.
The biparietal size of the fetal head is estimated together with the frontal-occipital size (LZR), measuring them in one plane (at the level of the legs of the brain and visual bumps). The change in the size of these two indicators is directly proportional to the duration of pregnancy.
After the 38th week, the configuration of the fetal head may vary, which also will determine the biparietal size of the fetal head. Thus, with a dolichocephalic configuration, the BDP of the fetal head will be less than normal.Ultrasound in pregnancy BDP head of the fetus in the norm and pathology
The biparietal size of the fetal head together with other indicators allows to determine such deviations in fetal development as a delay in fetal development of the fetus, hydrocephalus and a large fetus. If the indicator BDP head is more than normal, then do not rush to conclusions, you need to measure other parts of the fetal body. Uniform increase in all body sizes (head, chest, abdomen) gives reason to assume a large fruit.
If only the biparietal and lobinal-occular dimensions are increased (the distance from the most protruding outer edge of the frontal bone to the outer edge of the occipital bone), this is confirmation of the diagnosis of hydrocephalus. The cause of hydrocephalus in the fetus is intrauterine infection.
In those cases when the BDP of the fetus is less than the norm and all its other dimensions do not correspond to the gestation period, then a diagnosis is established - the retardation of intrauterine development of the fetus. The causes of ZVUR are intrauterine infection of the fetus, chronic hypoxia, due to fetoplacental insufficiency. If
Reducing the BDP of the fetus together with LZR without reducing other body sizes, speaks of microcephaly.
We examined the values of the index of the biparietal size of the fetal head, its value in normal and pathological deviations.