KTP norm. Coccyx-parietal size of the fetus by weeks in the table

2024 Author: Priscilla Miln | [email protected]. Last modified: 2023-12-16 00:21

Observation by a gynecologist of the development of pregnancy from the earliest dates is the key to a successful birth and the he alth of the unborn baby. Several informative criteria help the doctor to assess the dynamics of gestation. In the first trimester of gestation, the most important of them is the coccygeal-parietal size (KTP).

How to measure the CTE of the embryo

KTP is the length of the fetus in millimeters from crown to tailbone. You can get data on the CTE of the embryo on an ultrasound examination from 6 to 13 weeks of pregnancy. Before 6 weeks, the size of the embryo is still too small to be measured with an ultrasound probe. During this period, it is only possible to confirm the presence of pregnancy if a fetal egg is visualized in the uterine cavity. At about 6 obstetric weeks and 3 days, the size of the CTE reaches 7 mm. The embryo is already clearly visible on ultrasound, the heartbeat is determined, sometimes it is already possible to measure the heart rate.

In order to find out the CTE, an ultrasound specialist must apply measurement marks from the top of the head tococcyx when the embryo is in a calm, relaxed state. The uterus is scanned in several planes, the largest value of the coccygeal-parietal distance is selected. The data obtained is interpreted using a special table of the CTE norm during pregnancy by week of gestation.

Why is it correct to measure CTE, and not fetal growth

The distance to the coccyx is measured, not the full height, because the limbs of the embryo at this time are still too small. It is impossible to correctly assess the growth of the embryo up to 8-9 obstetric weeks. In addition, the sitting position is natural for a baby in the womb, with legs tucked under him. Therefore, fetal growth is not measured later in pregnancy.

To correctly measure a child's full height, an ultrasound specialist would first have to determine the CTE, the length of the tibia and lower leg, and then add all the results together. Such calculations have no diagnostic value and are impractical, because the rate of increase in CTE is directly proportional to the growth of the fetus and quite accurately allows you to set the embryonic gestational age.

How does CTE change by week of pregnancy

There are indicative KTR values for gestational age, approved by the medical community. The table of fetal KTR by week is given to the average indicators recommended by the World He alth Organization. Specialists rely on these data when conducting ultrasound examinations in pregnant women.

Determining the gestational age using KTP isthe most accurate research method. The error in the numbers in the norm when determining the KTR is only 3-5 days. If the deviation from the expected period is more than 5 days, you can suspect an incorrectly established obstetric gestational age or problems in the development of the embryo. Establishing the embryonic gestational age by measuring the CTE is possible with an accuracy of up to 90%. This method is much more reliable than determining the gestational age by the date of the first day of the last menstrual cycle.

Ultrasound screening and CTE values in the first trimester

If the pregnancy is uneventful, the first ultrasound screening is scheduled between 11 and 13 weeks of pregnancy. The study allows you to identify malformations and signs of chromosomal abnormalities, as well as assess the development of the fetus. The KTR rate at 12 weeks of gestation is 48-65 mm. The optimal time for ultrasound screening of the first trimester of pregnancy is 12 obstetric weeks and 3 days.

The compliance of the KTR of the fetus with the norm values is a positive factor in assessing the course of pregnancy. In addition to CTE, the length of the nasal bone and the size of the collar space are of great diagnostic value at screening at 12 weeks. Until the full 12 weeks, the embryo grows at about 1 mm per day. From 13 weeks, all the organs of the fetus are already fully formed, the baby begins to quickly gain in height and weight. The growth rate of CTE increases to 2-2.5 mm per day.

Why KTR can be more than normal

Small deviations from the norm should not worry the futurebaby's mom. Measurement errors with an ultrasound machine allow deviations from the norm within one week. If the CTE is greater than normal, more than one week ahead of time, the doctor may suspect the following factors:

• incorrect gestational age - the woman will be sent for a second ultrasound in 7-14 days;
• late ovulation;
• fetal development features (tall growth, large build).

Observation in dynamics allows you to get the most complete picture of the condition and development of the fetus. Clarification of the gestational age is necessary to determine the time of some studies and to set the expected date of birth. In general, the outstripping growth of KTP is not a dangerous sign.

What to do if the CTE is less than normal

When the KTR differs from the established normal size down by more than one week, the woman is prescribed 1-2 repeated ultrasounds. Sometimes an additional blood test for the hCG hormone is required. Slow fetal growth may indicate a worrying pathology, especially if the heart rate is more than 40 beats per minute below average.

In the complete absence of the heartbeat and motor activity of the fetus, a missed pregnancy is assumed. The fact that the pregnancy has ceased to develop is evidenced by the lack of fetal growth on repeated ultrasound. In this case, it is necessary to carry out curettage of the uterine cavity as soon as possible. The death of a fetus for a pregnant woman is the strongest stress and requires medical personnel to displaytact. But delaying surgery can lead to infertility and even death of a woman.

Nevertheless, far from always a deviation from the KTR norm indicates a pathological course of pregnancy. The reason may be an erroneously established obstetric term. Miscalculation of gestational age is common, especially if a woman's menstrual cycle is irregular. Physiologically small growth of the unborn child is also possible. In this case, upon repeated observation, the CTE of the fetus will increase by 7-14 mm.

Which CTE may require treatment

When there is an increase in CTE on a repeated measurement, but it is below the norm (less than 1 mm per day), the doctor may assume a threat of termination of pregnancy. This can happen due to improper adaptation of the female body to the bearing of the fetus, under the influence of external and internal causes, due to congenital genetic abnormalities of the embryo. The following medications may be prescribed to support pregnancy:

• gestagens to maintain the required level of the hormone progesterone;
• hCG hormone injections for better fetal development and preparation of the uterine cavity for gestation;
• antispasmodics to relax the muscles of the uterus;
• drugs that stimulate blood flow and oxygen saturation of tissues.

Timely identified problems and the appointment of drug therapy can normalize the course of pregnancy. Therefore, a woman should register with the antenatal clinic as soon as pregnancy is confirmed and visityour gynecologist in accordance with his recommendations.

Since when is KTR no longer informative

Starting from 13-15 weeks, fetal CTE data is no longer informative. Other criteria for the development of the unborn baby become more important. From the second trimester, body parts are studied in detail, such as the length of the bones of the limbs, the biparietal circumference of the head, the length of the nasal bone and the size of the collar space. The internal organs are also examined in detail, the structure of the heart and brain is assessed, the blood flow and the lumen of large vessels are checked in the Doppler ultrasound mode.

These parameters cannot be assessed in the first trimester, as the fetus is still too small. But by 16 weeks, the whole body is perfectly visible using a sonographic transducer. In this connection, after a full 15 weeks of pregnancy, KTR is no longer measured on an ultrasound study of pregnant women.

Who can interpret the KTR results

Only a specialist should interpret the results of measuring KTP obtained using an ultrasound study. Based on the coccyx-parietal size, a doctor observing a pregnant woman can draw conclusions about the successful course of pregnancy and fetal development. In the case of a significant deviation of the CTE from the average values, it is necessary to conduct a number of additional studies to determine the cause.

In addition to the norm of the KTR of the fetus by weeks of pregnancy, there are other features that determine the dynamics of the development of the embryo. Therefore, any appointment should be made by a gynecologist observing pregnancy. He has enoughamount of information to assess the totality of all factors affecting the course of pregnancy.