Fetometry is performed regularly at various stages of pregnancy – fetal size is determined by ultrasound. The data obtained during the survey, for many years, were subjected to statistical analysis, and on the basis of them was compiled a table with indicators of the norm by week.
It is the main parameter for a more accurate determination of the period and allows you to find out if there are any deviations in the intrauterine development of the baby. Knowing what it is, young parents themselves can, after an ultrasound examination, make sure that everything is in order.
The essence of the procedure
Ultrasonic fetometry is most often performed either by a transvaginal transducer, or traditionally through the abdomen. In the first case, no preparation is required from the woman. Classic ultrasound will show more accurate results, if in the early stages an hour before the procedure, drink 500 ml of water and do not empty the bladder. Filled, it will help improve visibility in the uterus. After 12 weeks, this is no longer necessary, since the amniotic fluid will perform this function.
The procedure is familiar to everyone: a special gel is applied to the stomach, and everything that happens in utero is displayed on a computer monitor. Modern programs allow you to automatically make measurements of the fetus, and the doctor already then compares them with the general table of norms for weeks. This allows you to specify the duration of pregnancy and timely identify the pathology in the development of the fetus.
Why is it called that? The term fetometry goes back to the Latin word fetus (translated as offspring) and the Greek metreo (meaning to measure, define).
Rates and deviations
It is useful for parents to know what the rate is, according to the table of fetometry, and when they talk about pathological deviations. Seeing a slight discrepancy between the true size and official figures, many begin to panic and draw the wrong conclusions, which in most cases turns out to be completely in vain.
- fetal data is fully consistent with the size in the table;
- they are behind or less than 2 weeks ahead of them (this period is valid for individual features);
- indicators are not on the same line, but randomly, but this difference is no more than 1 line: these discrepancies are permissible due to the abrupt intrauterine development of the fetus.
Everything else refers to cases of deviations. It is especially dangerous when fetometry of the fetus has once again shown that the same size is 2 or more lines more or less than the norm.
For example, a growing head circumference may indicate hydrocephalus, but to confirm the diagnosis, additional data obtained from Doppler and CTG and dynamic observation will be needed.
For comparison. If all the dimensions of the fetus fit into the norm indicated in the fetometry table, except, for example, the length of the thigh, this is not yet an indicator of pathology. Perhaps the parents or other relatives of the child are simply owners of very long (or, on the contrary, too short) legs.
If there are deviations, such serious diagnoses as intrauterine growth retardation, malnutrition, are confirmed by two doctors: not only an obstetrician-gynecologist, but also a medical geneticist. They assess the genetic predisposition of the fetus and determine the causes of the identified pathology (chromosomal abnormalities, bad habits, the age of parents, intrauterine infection, etc.).
It is very important that the obstetrician-gynecologist was primarily engaged in deciphering the obtained indicators: the ultrasound specialist only provides him with a summary list, which indicates what sizes and how much differ from the standard fetometry for a given period of pregnancy. What exactly parameters are taken into account during screenings?
Description of the main indicators
To understand what data fetometry of the fetus for weeks is contained in the tables, you need to know the symbols of these parameters and their interpretation.
- BPR – biparietal size, the distance between the parietal bones, describes the development of the nervous system.
- Db – thigh length.
- DG – the length of the leg.
- DN – the length of the nasal bone.
- DP – shoulder length.
- KTP – coccyx parietal size.
- LZR – frontal-occipital size.
- OG – head circumference.
- OG (DHA) – chest volume (chest diameter).
- Coolant – abdominal circumference.
- PJ – transverse diameter of the abdomen.
- PJ is the fertilized egg where the child develops.
- SJ is the sagittal diameter of the abdomen (measured in the anterior-posterior direction).
- TVP – the thickness of the collar space.
Such is the decoding of indicators, which are most often indicated in the table of fetometry. It may also include the lengths of other bones – the larger and fibular, ulnar, radial, and also the foot. But they no longer have such a meaning for identifying pathologies – they are used for comparison only as additional information.
Among other things, it is possible to calculate the weight of the fetus by fetometry carried out after 20 weeks of pregnancy. All calculations are made automatically by the ultrasound machine on the basis of the term, BPR, LZR, OJ, DB and OG. They give very accurate results and allow you to compare them on the table with the rules.
The first fetometry is prescribed at 12-13 weeks. Its purpose is to identify fetal malformations in the early stages of pregnancy.
This ultrasound screening does not determine the specific disease, but only points to markers typical of it. Based on the results obtained, additional studies may be assigned. All suspicions that have arisen are confirmed or refuted by invasive laboratory techniques.
Some indicators of fetometry can be refined. For example, specialists use the table of average CTE values during the first screening, since this size is very important for identifying abnormalities in the intrauterine development of the fetus.
Doctors refer to standard options for an increase in KTR for 1-2 weeks. If pregnancy is not complicated by diabetes of the mother and Rh-conflict, this may mean that the baby will be born a real hero and his weight will be more than 4 kg, and this in some cases may be an indication for a cesarean section.
These are the important data that the first fetometry gives to the specialists.
About the timing. The first ultrasound screening is carried out during this period due to the TVP indicator. Until week 11, it is so small that it cannot be measured. After 14 weeks this space is filled with lymph, which distorts the results of the study. This parameter is a marker of the majority of chromosomal abnormalities of the fetus.
The time frame for the second ultrasonic fetometry should be within the following time frame:
- not earlier than 16 weeks;
- no later than 20;
- the best option is week 17, which, if deviations are detected, will allow more accurate additional genetic examinations to take place;
- Sometimes ultrasound is carried out for 21-22 weeks, but this is the most extreme and undesirable time.
The first ultrasound screening gives the most accurate results, but often even they are not enough for a reliable diagnosis. To do this, many indicators need to see in the dynamics. This is exactly what the second fetometry data demonstrates.
It performs the following tasks:
- to identify defects that can not be determined in the first trimester;
- confirm / refute the diagnosis previously made on the results of the first screening;
- determine the risk level of suspected fetal abnormalities;
- detect abnormalities in the formation of a small organism.
Fetometry II trimester is assigned only to those women who according to the results of the first ultrasound were at risk.
Approximate rates of ultrasound at this stage of pregnancy are presented in the following tables.
Forearm Bone Length
If for some reason the dates of the second fetometry were shifted, you can use a table with averages from 21 to 27 weeks:
Having studied the data of the second fetometry, the gynecologist can refer the woman for a consultation to genetics or independently assign invasive techniques for diagnosing suspected pathologies. In cases where the diagnosis is still confirmed, a decision is made about the future of the pregnancy.
If therapeutic adjustment is not possible, artificial induction of labor is carried out (for artificial childbirth, read our article). If the detected pathology is reversible, treatment is prescribed as soon as possible in order to save the baby.
A third fetometry can be prescribed for any day of the third trimester of pregnancy. The optimal period is 32-33 weeks. Since at this stage, the case is nearing childbirth, ultrasound is performed more thoroughly than before.
For example, the face of the baby is already perfectly visible, which makes it possible to identify pathologies such as cleft palate or cleft lip. The doctor finds out how well the fetus is developed in accordance with the gestational age.
It is usually not recommended to conduct such studies after 34 weeks. However, there are cases when they are appointed immediately before the birth (at 37-38 weeks) in order to make a final decision on cesarean section or natural birth of the baby.
Table of average values of the third fetometry by week
If there are deviations at this stage, the woman is offered hospitalization. With the negative dynamics of the testimony obtained, doctors can decide on the stimulation of preterm labor.
Useful information. Everything around (women, and often the doctors themselves) love to talk about the importance of the first two fetometry and the optional third. But after all, only it allows you to make the right decision on how to carry out the upcoming birth with minimal losses for the mother and baby.
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Information from fetal fetometry tables is for informational purposes only. It is not recommended for parents to draw any independent conclusions comparing the results obtained with the norms, because they do not always reflect reality and require mandatory interpretation of specialists.