Normal fetal heart rate, diagnosis and treatment of abnormalities

When the fetus has a heartbeat and how long can you hear it?

Women who have been trying to get pregnant for a long time and finally get the coveted 2 strips on the test, coming to my appointment, are keenly interested in how long the fetal heartbeat can already be heard on an ultrasound scan, and are upset if it is still not possible at 5.5-6 weeks catch him.

The heart is formed already in the 3rd week after conception. First, it is a tubular organ, which eventually divides into 4 chambers.

The first contractions occur when the size of the embryo is 3-4 mm (approximately on the 21st day after fertilization). In the fifth week, this is still a weak arrhythmic beating, which is not recorded by ultrasound sensors. During this period, the rhythm is set by a group of cells that subsequently form the sinoatrial node. But from 6.5 weeks, the rhythm improves and the fetal heartbeat appears with a frequency of more than 100 beats per minute.

In in vitro fertilization (IVF), the countdown starts from the day of embryo transfer into the uterine cavity (then the heartbeat can be detected 5-5.5 weeks after the procedure). Monitoring the development of pregnancy in the early stages in such women is carried out using a dynamic assessment of the level of hCG.

Further, the beating rate of a small heart gradually increases until the 8-12th week (up to 170 / min.), Then, by 6 months, is set at 140 beats per minute.

Until the 19th week, the autonomic nervous system does not affect the rate of contractions. But from the 20th, in response to the child's movements in the uterus, the heart rate reflexively slows down. And by accelerating the rhythm during wakefulness, the baby reacts only from the 28-29th week.

Specifications

Throughout pregnancy, according to the characteristics of the fetal rhythm, it is possible, without interfering with the woman's body, to monitor the development, physical condition of the child, notice violations in time and prescribe therapy.

Physical characteristics of the heart rate of the embryo

Fetal heart rate is a variable value. The rhythm changes constantly: with the movements of the child in the womb, during rest, after eating by the mother, as a reaction to a drop in serum glucose.

Due to the peculiarities of the circulatory system of the embryo at different stages of gestation, the heartbeat is determined by several factors:

• the stage of the formation of the chambers of the heart;
• the presence of structural abnormalities;
• ingrowth of fibers of the autonomic nervous system into the myocardium;
• a change in the fetal rest / activity cycle;
• maternal blood glucose levels;
• the amount of hemoglobin in the blood;
• the state of the uteroplacental blood flow;
• the presence of compression of the umbilical cord;
• the state of the amniotic fluid;
• the general state of health of the mother.

Table of normal indicators for different periods

The fetal heart rate changes depending on the timing of pregnancy. Up to 9-10 weeks, the frequency progressively increases to 170-180 / min., And then, by the 33rd week, gradually stabilizes at around 140-160 / min.

Table of fetal heart rate by week of pregnancy

Some of my patients try to determine the sex of the unborn child using the fetal heart rate during the first ultrasound scan. They rely on the theory that a girl's heart beats at a rate of 150-160 per minute, and a boy's - 140-150. But from the point of view of medicine, as well as my observations, the chances of guessing the sex in this way are 50%: many factors affect the rhythm of the embryo, and in no way its gender. Moreover, these figures do not fit into the tabular fetal heart rate by week, corresponding to the date of the first ultrasound screening.

How to listen to a fetal heartbeat

It is possible to assess the indicators of fetal cardiac activity using:

• Ultrasound (in the early stages with an intravaginal sensor, then - with a transabdominal);
• cardiotocography (CTG);
• fetal dopplerometry;
• direct auscultation with a stethoscope.

Determination at home

Modern developments in the field of medical devices offer portable devices that record fetal heart rate - fetal monitors.

This device allows you to determine the indicators of the baby's heart activity, regardless of time and place, or simply enjoy the sound of a beating heart.

The Doppler design is extremely simple:

• small size housing with digital display and buttons for volume control, recording and playback, which is powered by batteries;
• directly the sensor, which is connected to the base with a wire;
• headphones.

It is possible to determine the heartbeat using a fetal monitor from the 12th week of pregnancy.

The cost of such devices in Russia is from 2 to 7 thousand rubles. More expensive models can transmit sound waves to the uterus. Manufacturers offer, playing slow music, to calm down a raging baby in the womb.

How to use a stethoscope and what it is

An obstetric (fetal) stethoscope is the simplest device for determining the functional state of a child and diagnosing fetal distress, which is available in every antenatal clinic.

Auscultation of the abdomen of a pregnant woman is carried out from the second trimester during each of her visits to the obstetrician-gynecologist.

During auscultation by an obstetrician-gynecologist of the abdomen of a pregnant woman with a stethoscope, in addition to the heart sounds of the child, they listen to:

• peristaltic noises of the intestines and uterus;
• the sound of the movement of blood through the vessels of the umbilical cord;
• movements, tremors of the fetus;
• the beating of the abdominal aorta (should completely coincide with the pulse of the pregnant woman).

Reasons that make it difficult to listen to heart rate:

• significant fatty layer of the anterior abdominal wall;
• attachment of the placenta to the anterior wall of the uterus;
• polyhydramnios.

Technique: the study is carried out when the pregnant woman lies on her back. Before listening, I determine the position, position, type and presentation of the fetus (its location in the uterus relative to the birth canal). The place where you need to apply the stethoscope depends on this. The heartbeat is best heard from the side of the back of the fetus, between its shoulder blades.

The wide end of the fetal stethoscope is pressed against the abdomen, and the other - tightly against the ear. The clarity, the rhythm of the heart tones are determined, the heart rate is calculated for 1 minute.

You can also listen to heart sounds using a standard phonendoscope.

Ultrasound

Ultrasound examination during pregnancy is an extremely important and reliable method for diagnosing fetal anomalies, monitoring its development, and determining the tactics of delivery.

It is safe for the mother and the fetus, fast, affordable and informative research, which does not require preliminary preparation (except for a full bladder in early pregnancy).

Assessment of fetal heart rate during ultrasound is most relevant until the second trimester. Further, the heartbeat is listened to with a stethoscope and CTG.

In addition to the rhythm, ultrasound examination at different stages of gestation determines:

• the number, position and attachment of the ovum;
• size, functional state of the placenta and umbilical cord;
• the amount of amniotic fluid;
• size, weight of the child, the presence of intrauterine growth retardation syndrome;
• position, position, type and presentation of the fetus (head, pelvic, transverse, oblique);
• all internal organs are visualized, which allows early detection of various developmental anomalies and chromosomal pathologies;
• condition of the cervix.

The data obtained during the ultrasound study, together with CTG, allow us to determine the biophysical profile of the fetus - an integrated indicator that most accurately predicts the possible intrauterine death of the embryo.

Further tactics directly depend on the amount of points:

• 12-8 - the normal state of the fetus;
• 7-6 - dubious result (hypoxia is possible), dynamic observation, daily CTG, counting movements, dopplerometry of uteroplacental blood flow in dynamics;
• less than 5 - severe fetal distress, threat of antenatal death of the child, immediate delivery.

Cardiotocography: description of the method and its information content

CTG is a method for assessing the condition of the child by means of parallel registration of the baby's heartbeat and the contractile activity of the uterus. This is an affordable non-invasive method for early diagnosis of fetoplacental circulatory disorders and control of the treatment.

The monitoring result is presented on a specially cut sheet in the form of two curves. Modern cardiotocographs are equipped with the function of mechanical registration of fetal movements.

The autonomic innervation of the heart matures by the 32nd week of gestation. Therefore, acceleration (acceleration) and deceleration (deceleration) on CTG recorded before the third trimester can only be caused by the influence of the maternal organism and intrauterine conditions on the sinoatrial node.

CTG, recorded after the 32nd week, reaches the maximum diagnostic value in assessing the functional state of the fetus. During this period, the myocardial reflex, sleep and wakefulness regimes mature.

The CTG procedure is carried out for at least 40 minutes, since it is necessary to examine the child's cardiac activity during the period of his activity. The duration of the baby's sleep fluctuates in the range of 15-30 minutes, and during this period of time the indicators will coincide with those if his condition is disturbed.

CTG can be recorded in the supine or half-sitting position. A sensor is attached to the pregnant woman's stomach in the projection of the fetal back (for twins, one for each child), and a button is given to her hands, which she must press as soon as she feels the fetal movement (kicks, turns, stretching). This will help you better assess your heart rate variability.

Based on the results of CTG, the following are assessed:

• basal rhythm (average heart rate for 10 minutes of measurement);
• variability (the degree of deviations from the basal rhythm) - the number and amplitude of instantaneous oscillations are calculated;
• acceleration (acceleration of heart rate by 15 beats / min. and more lasting over 15 seconds);
• deceleration (slowing down the rhythm) - types Dip1, 2, 3.

The obtained indicators are converted into points according to Fisher's criteria (Fig.).

Signs of a normal CTG:

• basal heart rate 110-150 / min;
• variability 5-25 bpm;
• lack of decelerations;
• more than 2 accelerations in 10 minutes.

If the above criteria are met for 20 minutes, CTG is not recorded further.

Pregnancy management tactics, depending on the number of points:

1. 9-12 - satisfactory condition. There is no threat to the fetus.
2. 6-8 - signs of fetal hypoxia. KTG registration should be carried out daily.
3. 0-5 - pronounced fetal distress, the threat of antenatal death. Urgent hospitalization and delivery.

In case of doubtful CTG results, functional tests are additionally carried out to assess the reserve capabilities of the fetal circulatory system and increase the reliability of the diagnosis.

1. Non-stress test (NST). Tracking changes in fetal heart rate in response to its own movements, thereby assessing the work of the myocardial reflex and, accordingly, the baby's nervous system. The absence of a heart rate response is an indication for an oxytotion test.
2. Oxytocin contractile test. Tracking the reaction of the fetal heart in response to uterine contractions.
3. Sound stimulation test. Using a vibroacoustic system, the doctor wakes up a sleeping baby, thereby potentially increasing its activity and information content of the study and reducing the frequency of false-positive CTG results.

But it is worth noting that cardiotocography registers violations only at the time of recording, and the point system has a reliability of about 75%. To predict the outcome of pregnancy, these data can be used exclusively in combination with other diagnostic methods.

How not to miss pathology: common signs of problems

Usually, auscultation with an obstetric stethoscope and CTG at a gynecologist's appointment can show fetal cardiac abnormalities in time.

In the case of a complicated pregnancy from the second trimester, a woman can keep a daily diary of fetal movements (Pearson test). It helps to monitor the baby's condition in order to seek medical help on time.

If in 12 hours the child moves less than 10 times, you should immediately consult a doctor.

Clinical case

Patient B., 26 years old, was seen by me about the 1st pregnancy. Clinical analyzes at registration were normal. Screenings I and II did not reveal any pathology. According to the results of an ultrasound scan at 32-33 weeks, one fetus was identified in the cephalic presentation, the development of which confirmed the gestational age, no structural abnormalities were found. Gains in weight and volume of the abdomen, the height of the fundus of the uterus corresponded to the prescribed ones. During the visit for a period of 34-35 weeks according to the results of CTG, the patient received 9 points. To be on the safe side, I asked her to keep a diary of fetal movements and explained when to seek help.

On the third day of measurements in 12 hours, the pregnant woman felt only 7 shocks and came for an unscheduled appointment. CTG showed signs of fetal hypoxia and distress. The patient was urgently referred to the perinatal center, where an umbilical cord entanglement with compression of her vessels was diagnosed and an emergency caesarean section was performed. A boy was born weighing 2250 grams, height 46 cm, Apgar score 5-7. Discharged home after 21 days.

Also, relatively inexpensive and easy-to-use portable fetal monitors will help a woman to independently listen to the baby's heart rate at any time of the day. You can ask the doctor to write out the fetal heart rate by week and compare the results with the tabular ones.

Signs of possible deviations:

• rare fetal movements;
• insufficient weight gain;
• the volume of the abdomen has ceased to increase;
• there were pulling pains in the lower abdomen;
• not passing uterine tone;
• suspicious vaginal discharge.