Fetal heartbeat by week: features and norms in the table

The fetal heartbeat is an important characteristic that allows doctors and mothers to understand how well the baby is feeling in the womb. They begin to measure it earlier than other parameters of vital activity and continue throughout pregnancy and childbirth. In this regard, mothers have many questions about heart rate.

How is the heart formed?

The baby's heart is one of the first to form. The woman does not yet realize that she is pregnant, and the crumbs are already undergoing intensive processes of organogenesis of the heart and great vessels. This process begins in the second week of pregnancy. (from the date of conception).

In the embryo, in the first week of its existence, two heart buds are formed - endocardial tubes. They gradually merge into one, but two-layer. The most rapid growth of the tube occurs at 3 weeks of gestation. (the first week from the beginning of the missed period). Despite its miniature size, the heart tube of the embryo has a rather complex structure: it has five sections, of which the atrium, ventricle, venous sinus will form, there is an arterial bulb and a trunk.

A baby's heart acquires its characteristic appearance at 5 weeks from the day of conception, that is, at 7 obstetric week. At this point, the heart has already been divided into right and left halves, separated by two partitions.

It is noteworthy that the formation of the heart does not occur where this organ is usually located, but in the cervical region. As the organ develops, it gradually descends to where the chest will later be. On the way there, the heart turns over, and those sections that were formed on top are at the bottom.

This process is very complex, and therefore any violations in it can cause gross pathology, for example, the heart will remain in the cervical region or will not turn over, and then its top will be turned down.

At 4 weeks of embryonic development, an interventricular septum is formed, the organ is divided into 2 parts. At the 6th week of the baby's development, an oval window forms in the septum and the heart becomes three-chambered. At week 7, the process of formation of another septum begins and by the end of week 8, the process of formation of another septum begins and the heart becomes four-chambered, such as that of each of us.

The embryo's heart begins to beat at the end of the 5th week of pregnancy, this can be recorded according to the results of ultrasound... There are no other ways to hear a tiny heart beating in the early stages.

The period from 2 to 8 weeks of embryonic term (from 4 to 10 weeks of gestation) is critical.

With any teratogenic factor, the formation of the heart and blood vessels may be disturbed, which is fraught with the development of defects, sometimes incompatible with life. The bad habits of a woman, an unfavorable environmental situation, harmful factors of production, etc., can have such an impact.

When and why are they measured?

From the end of the 5th week until the very moment of delivery, the fetal heart rate is measured at each ultrasound examination. This is not a tribute to tradition, but an important characteristic of the baby's condition at the time of the examination. The frequency with which the heart of the crumbs beats is indicated in the ultrasound protocol by the abbreviation heart rate - heart rate.

At different stages of pregnancy, additional methods of listening to the baby's heart appear. From about 18 obstetric weeks, echocardiography can be done. Ultrasound with a Doppler and in color gives an idea not only of how well the heart is formed and how it beats, but also of how blood circulates in the great vessels.

From the middle of the second trimester, the auscultation method is used - listening with an obstetric tube with a wide distal end (stethoscope). This is in the office of every obstetrician-gynecologist and usually every planned appointment of a pregnant woman begins with the listening procedure... This method does not allow you to calculate the heart rate in a numerical value, but it gives the doctor an idea of how rhythmically and clearly the baby's heart is beating, and also to assume its presentation - when a heartbeat is detected below the navel, women talk about head presentation, with a beating in the navel, to the right or to the left of it, suggest a transverse arrangement of the crumbs, and if the heartbeat is heard above the navel, with a high degree of probability the baby is in breech presentation.

But the method is not very accurate, especially with polyhydramnios, when the heart rhythms are poorly listened to, with oligohydramnios, with pregnancy with twins or triplets, and also if the mother is obese or with the placenta located on the front wall.

From the 30th week of pregnancy, another method becomes available - CTG (cardiotocography). It is done both according to indications and for monitoring all expectant mothers. The method is based on the registration of two indicators by sensors - the heartbeat and movements of the fetus are recorded, and the connection between movements and increased heart rate is monitored (this is typical for babies).

In the process of childbirth, it is also often necessary to register heart rate and contractions by attaching CTG apparatus sensors to the woman's abdomen. This monitors the condition of the fetus during childbirth.

At home, a woman can hear a baby's heart beating in several ways, but all of them are intended solely to satisfy the curiosity of her and her future father. A woman needs special medical knowledge to understand what this or that change in the rhythm of the beating of a child's heart means. We are not talking about situations where home heart rate control is recommended by a doctor - in this case, special portable fetal monitors are used, which are given to the expectant mother for a while so that she can follow the doctor's recommendation.

An obstetric stethoscope can also be used for home listening - after 24 weeks of pregnancy, but this method is not available to the woman herself, since someone else, for example, her husband, will listen. Today, fetal dopplers are on sale - small devices with an ultrasound probe. You can use it at home from 13-14 weeks of pregnancy.

The main difficulty lies in finding the listening point, which, as practice shows, does not work right away. You can use a regular phonendoscope - after 32 weeks of pregnancy, or try to listen to the baby's heart with your ear through the abdominal wall, but for this the baby must be conveniently located - facing the abdominal wall.

Heart rate is an indicator about which doctors have no consensus. It is more often considered that it does not have high diagnostic accuracy, since there can be many reasons why the heartbeat can slow down or speed up, and even the usual excitement of the mother or her unimportant state of health will certainly affect the heart rate result. Why then measure your heart rate?

First of all, for the diagnosis of pregnancy itself - at 5 weeks... A small fertilized egg may be invisible in the uterine cavity, but its beating and characteristic sound will not allow the doctor to view the baby. Secondly, the baby's heart muscle reacts to any changes in its condition, which can be important as part of a comprehensive assessment of the fetus's condition. As an independent measure that allows you to make a diagnosis, heart rate measurement does not act. But it favorably complements the information that can be collected during the ultrasound scan, laboratory tests.

But in the process of giving birth to a baby in a maternity hospital, measuring heart rate is a direct indication of his condition. Acute hypoxia during childbirth is very dangerous for a child, and the prognosis will depend on how quickly doctors learn about it and decide on the further management of childbirth.

Standards

Before talking about heart rate norms, it is important to understand that in the process of forming the cardiovascular system, the baby's heart beats unevenly. After 8 weeks, the rhythm usually becomes more confident, clear.

Much in this parameter is individual. If a woman suffers from toxicosis or has a cold or acute respiratory viral infection, the baby's heartbeat always increases, and the examination during this period will give overestimated values. If the mother lay on her back for a long time, as a result of which the vena cava was squeezed by the pregnant uterus, then the heart rate may be reduced, but after changing the position of the body, after a while it will return to normal.

The child in the womb is asleep and awake, and in these two states he has a different heart rate... In the late stages of pregnancy, the baby is quite emotional, he hears a lot, feels, may be frightened, and the heart muscle is the first to respond to this and give out high readings of the heart rate.

The rates for early and late dates differ, as can be seen from these tables.

Table of normative heart rate values - early dates

Table of standard values of heart rate - second half of pregnancy

Can these norms be considered rigid? No, since a huge number of factors can affect the heart muscle of the crumbs. A slight deviation of the heart rate in one direction or another is quite acceptable.

If the doctor has certain concerns about the health and condition of the baby based on the heart rate results, he must prescribe additional examinations.

Deviations and reasons

And yet, the discrepancy between the beating of a child's heart and the average standards cannot but scare women. Hearing from the doctor that the heart rate does not correspond to the norm, the expectant mother begins to worry, which further exacerbates the situation - during stress, the female body produces an increased production of adrenaline and cortisone (stress hormones), which does not go unnoticed for the heart muscle of the baby. Therefore, let's calmly consider the possible causes of deviations from the norm.

Decreased heart rate

Your baby has been diagnosed with bradycardia. The heart beats slower than necessary for the duration of pregnancy. Most often this happens in the final, third trimester, when the baby becomes cramped.when the placenta begins to age and worsens to cope with its gas exchange and nutritional functions.

Fetal bradycardia is a condition in which the heart rate is reduced to 110 beats per minute or lower. Please note that during CTG, the heart rate may drop to such values, but then it returns to the original numbers. Bradycardia is a persistent decrease in heart rate that is observed throughout the entire examination.

By itself, bradycardia does not indicate any specific disease, but doctors treat it very carefully, since it always says that the child's condition is significantly impaired. A slow fetal heart rate can be heard if a woman is leading an unhealthy lifestyle - smokes, uses alcohol and drugs during gestation. Often, the baby's heart rate slows down due to the mother's anemia (It is for this reason that the deviation of the heart rate towards a decrease is observed more often in the third trimester).

If a woman has oligohydramnios or polyhydramnios, then the condition of the fetus may also be impaired. Violation of the amount of amniotic fluid is diagnosed quite easily, and throughout pregnancy such women are closely monitored. The reason may be the woman's intake of drugs with hypnotic effects, the abuse of sedatives. Sometimes persistent bradycardia indicates congenital malformations.

The slowed down frequency of the beating of a child's heart is always an alarming sign, since it indicates that the baby is in a state of decompensation, that is, the violation is at least chronic, and the crumbs' body no longer has the resources and opportunities to compensate for what it does not receive. Bradycardia may suggest severe intrauterine chronic hypoxia (oxygen starvation), placental insufficiency, placental infarction, severe Rh-conflict in a Rh-negative woman with an Rh-positive child, mechanical asphyxia with an umbilical cord (entwined around the neck).

The response of doctors to bradycardia should be immediate. It is necessary as soon as possible to establish the cause that led to the condition and eliminate it... If it is not possible to establish or eliminate it, an early emergency caesarean section is performed to save the child's life and in his interests.

The only case when bradycardia is not an indication for urgent hospitalization is the identification of a slowdown in heart rate due to temporary circulatory disorders (squeezed vena cava, umbilical cord squeezed by the child himself inside the uterus). Usually a woman is asked to walk and walk for half an hour, return and be tested again. Physiologically caused bradycardia is not confirmed on repeated examination.

If again the heart rate results are underestimated, the woman is hospitalized, since her condition and the condition of the crumbs may require medical intervention at any time.

Increased heart rate

Overestimated fetal heart rates are less dangerous than lower ones. It has already been said that fear, stress may well be the cause of such examination results. But even if it's not about stress, the often beating heart is a sign that the baby is struggling, his condition is compensated. High heart rate values are called tachycardia, and they talk about it if the heart rate exceeds 175 beats per minute... The deviation must also be stable and persistent. The exception is the period from 8 to 11 weeks of pregnancy, when a high heart rate rhythm is a physiologically determined norm.

The reason for the increase in frequency may be the mother's bad habits, as well as some of her diseases. For example, with hyperfunction of the thyroid gland, when the level of its hormones rises, there may well be a change in the frequency of the heartbeat in both the baby and his mother. In the case of severe toxicosis, if vomiting for a woman becomes habitual, the likelihood of dehydration increases, and in this case, the baby's heart is listened to with the definition of tachycardia. The cause of fetal tachycardia can be mother's heart disease, disorders in the functioning of her kidneys.

A child may also have his own personal reasons for a rapid heartbeat - structural abnormalities of the placenta (its defects), the presence of intrauterine infection, hypoxia in the initial stages.

Oxygen starvation, if it started recently, is perfectly compensated by the child's body, forcing its adrenal glands to work a little more actively. While the state is compensated, the heart rate is increased, as soon as bradycardia occurs after that, it is said that the fetus's condition has worsened - it has ceased to fight and compensate for the lack of oxygen. In the absence of urgent assistance, he may die.

It should be noted that too frequent heartbeats are also characteristic of some chromosomal abnormalities. For example, a fetus with Down syndrome often suffers from concomitant tachycardia. But to diagnose chromosomal abnormalities, listening to the heart is not enough, for this there is a system of diagnostic measures.

Boy or girl?

Speaking about fetal heartbeat, it is difficult not to dwell separately on the topic of determining the sex of the unborn child by heart rate.Despite the fact that it is the 21st century, many continue to believe that the frequency of the beating of a child's heart can indicate the sex of the embryo. They believe because they want to believe, and otherwise it is impossible to determine the sex of the baby in the early stages - an ultrasound scan up to 15-16 weeks cannot reliably answer the question of which child a woman is expecting.

Experts say that there is no relationship between the sex of the baby and his heartbeat.... The sex of the baby is formed at the time of the merger of the sex cells of the parents. If in the last pair the chromosomes coincide in type XX, a girl will be born, if XY is a boy. Organogenesis of the heart occurs the same in embryos of both sexes, the organ and its functions develop the same week, otherwise doctors would have two diagnostic tables - one with a heart rate for boys, the other with a heart rate for girls.

At the same time, women's forums are full of messages and discussions on this issue, as if no one hears the opinion of experts. The girl is credited with a more frequent heartbeat, the boys are more rare. In girls, experts in folk methods of sex determination say, hearts beat inconsistently, indistinctly, and in boys - rhythmically. In fact, a confused and fuzzy rhythm of the beating of a child's heart appears only in one case - if the child has congenital heart defects.... And there is no difference, a boy inside the womb or a girl. Sick hearts really beat differently from healthy ones.

If the child is healthy, then his gender does not matter - the heart will beat rhythmically and clearly in both girls and boys.

To find out the gender, if it is important, you need to do an ultrasound scan after 14 weeks or donate blood as part of a non-invasive prenatal DNA test... Ultrasound gives an answer with an accuracy of 80%, a DNA test - with an accuracy of 99%.

Another a common myth about heart rate says that during pregnancy after IVF with cryoprotocol, the hearts of babies beat slower... As you can see from the above, this is not true. Cryopreservation of germ cells and embryos reduces their viability, but does not affect the development of the embryo if implantation is successful.

Attentive mothers listen to the heart of their baby during an ultrasound scan or at home on their own with the sinking of their own heart, tenderness and calmness appear, the woman's stress level at this time decreases and this is the pure truth.