Important indicators, which are determined by the method of ultrasound diagnostics, help to assess the pace of development of the baby in the womb. One of the key ones is biparietal size or BPR. What it should be for different periods, and what the deviation of the BPD from the norm may indicate, this article will tell.
What it is?
With the advent of ultrasound diagnostics, the intrauterine development of babies has become much clearer, because before it would have occurred to anyone to measure anything, and even in the early stages of an unborn baby. Today, the measurement of the main dimensions of the fetus at different times is considered a mandatory component of pregnancy management.
Among the numerous sizes that are evaluated by ultrasound specialists in order to understand whether the growth rate of a baby in the mother's womb corresponds to the average statistical standards, one of the main ones is BRP. The biparietal size is recorded already from the end of the first trimester, the beginning of the second, and until the very birth. It is from this size that the ultrasound protocol of a pregnant woman always begins.
Size is the distance between the parietal bones in the transverse plane. In order to obtain such an image, the ultrasound specialist needs to place the scanner transducer so that the head is on top.
Babies who are just growing up in a cozy mother's tummy have a head that is not at all the same shape as ours - it is round, oval. Therefore, the distance between the parietal bones alone will not give an accurate idea of the growth rate of the baby's head. BPR is always "adjacent" to another size - LZR (this is the frontal-occipital dimension, which is the distance between the frontal and parietal bone). Two segments (LZR and BPR) are perpendicular to each other. Biparietal size indicates the width of the baby's head.
Why should you measure?
The biparietal size indicates how the head grows, how the amount of medulla increases. From about 13 to 21-22 weeks of pregnancy, this indicator is important in order to clarify the gestational age. Determination of the gestational age by BPD during this period of gestation has a fairly high accuracy, an error of a maximum of 5-7 days is considered permissible. Pregnant women after IVF and women with an irregular cycle who do not remember the date of their last menstruation, such a "reconciliation" of terms is simply necessary.
After 28 weeks of pregnancy, the relevance of bipolar disorder as a method for specifying the term is lost. Children grow at different rates, each has its own genetic program, which each baby owes to mom and dad, in other words, there are big-headed, large babies, and there are tiny crumbs with a small head.
From the third trimester, BPD, together with the circumference of the baby's tummy and the length of the femur, indicates not age, but the estimated weight of the fetus. This value is usually very interesting for expectant mothers, as well as for their attending physicians, who must make a decision about the tactics of obstetrics in advance - if the baby is too large, it is safer for everyone to have a planned cesarean section.
Throughout pregnancy, the dynamics of bipolar disorder indicates the rate at which the baby's brain is growing. And significant deviations can be a sign of malformations and trouble.
About the norm
Future mothers who expect that there is somewhere some wonderful table, which clearly states what the size of BPD should be for a given week of pregnancy, will be disappointed, because BPD is a very variable criterion, and therefore cannot be expressed in one number. After an ultrasound scan, doctors use a comparison with the so-called nomograms - these are special diagnostic tables compiled using percentiles.
To understand the nomogram correctly, you need to know that The 90th percentile is the prevalence in 90% of cases or less, the 50th percentile is the repeatability in 50% of cases or less, the 10th percentile means that the trait occurs in 10% of cases or less. As long as the size of the BPD measured for your baby fluctuates within percentiles, this is not considered a pathology.
Note! In different regions of Russia, taking into account some ethnic, racial and national characteristics of the size of the head of the population, there are their own tables-nomograms. Consider this when trying to understand whether your baby is developing correctly according to the norms of fetometry.
Pregnant women in Yakutia have some norms, expectant mothers in Dagestan - others, in the capital region - others. If you cannot find a table with your regional norms on your own, try to find a nomogram according to the principle of territorial proximity - take with the norms for a neighboring region, the error will be small. Here is an example of such a nomogram:
BPR nomogram (with regional significance for Moscow, Moscow region and central regions)
Possible deviations and their reasons
Before the expectant mother falls into a stupor, if the size of the fetal bipolar disorder does not correspond to the boundaries of the percentiles, it should be noted that a single detected deviation, if it is no more than 2-3 lines on the nomogram in one direction or another, does not indicate pathology. If the size of the head is less than or more than the characteristic time by more than 3 weeks, then additional diagnostics are needed to identify the causes.
By one measurement, no one will say about pathology, it is imperative to assess the situation in dynamics. To do this, the expectant mother may be asked to come for an ultrasound scan once a week several times in a row. And only then will they start looking for the reasons.
Increasing the head size
The reason for a significant excess in size may be macrocephaly, which, in turn, occurs with congenital defects and hydrocephalus (dropsy of the brain). Usually with hydrocephalus, dilated cerebral cavities filled with cerebrospinal fluid are additionally noted. Such consequences can lead previous infection for a period of 13 to 27 weeks, congenital intrauterine tumors, trauma, severe hypoxia, non-closure of the spinal column.
If hydrocephalus is found in the second trimester, termination of the pregnancy is usually recommended. If the “find” falls on the second half of the third trimester, an additional examination is carried out and the tactics of treating the baby are chosen immediately after birth. This issue should be resolved by a qualified pediatric neurosurgeon.
The large head may be due to the overall size of the fruit. In this case, a decision is made on how to carry out childbirth in advance. On the recommendation of the Russian Ministry of Health, a large fetus is one of the indications for the appointment of a planned cesarean section.
If the baby hero is healthy, then nothing else is done, but if large sizes are not associated with heredity, but with the mother's diabetes mellitus during the gestation period, then the pregnancy is continued by the gynecologist and endocrinologist together, the woman is put on a therapeutic diet, in some cases it is possible the appointment of insulin.
Reducing head size
The decrease is called microcephaly. The reason may lie in heredity (perhaps all members of this family have small heads). In this case, there is absolutely nothing to worry about. From pathological reasons, one can note non-closure of the spine, a violation of the development of the spinal column, while the head generally changes shape and becomes similar to a banana or lemon. True microfezaly can be a consequence of brain underdevelopment, partial or complete absence of it (anencephaly).
If microcephaly is found not associated with genetic data, termination of pregnancy in the second trimester is recommended. If the parents refuse, then they are surely warned about what the life of a child with microcephaly can be like - he will not be able to move fully, there will be no sensitivity of the limbs, he may be tormented by severe chronic pain, the child will suffer from fecal and urinary incontinence, his spine will not develop right.
Intrauterine infections that affect the embryo in the first trimester of pregnancy can lead to the formation of microcephaly. But with infection after 28 weeks, the infection is more severe, and the death of the child and a significant decrease in the size of the head are not excluded.
A decrease in the head is characteristic of many chromosomal abnormalities, for example, for Patau, Edwards, Down syndrome. It happens that microcephaly is associated with genetic disorders of bone formation. At the same time, there are other malformations of bones: twisted limbs, fractures, deformities. Often such pathologies are not compatible with life.
Additional application
BPD is important in order to be able to calculate the so-called cranial index - a value indicating that the development of the baby has stopped, and this index will also make it possible to find out about how long ago this happened.
In order to calculate this index, you need to divide the BPR value by LZR and multiply by 100. If the number is more than 83, this is the norm.
If the baby died in utero, then after a few days there is a decrease in bipolar disorder, and the lower the index, the more time has passed since the fading.
