What is normal blood pressure by age? Blood pressure: what is considered normal, how to measure it, what to do if it is high and low? Blood pressure in childhood and adolescence

The listed manipulations allow the specialist to collect the necessary minimum information about the patient’s health status (make an anamnesis) and indicators of the level of arterial or blood pressure play an important role in the diagnosis of many different diseases. What is blood pressure, and what are its norms for people of different ages?

For what reasons does blood pressure increase or decrease, and how do such fluctuations affect a person’s health? We will try to answer these and other important questions on the topic in this material. We will start with general, but extremely important aspects.

What is upper and lower blood pressure?

Blood or arterial (hereinafter referred to as blood pressure) ) - This is the pressure of blood on the walls of blood vessels. In other words, this is the pressure of the fluid of the circulatory system, exceeding atmospheric pressure, which in turn “presses” (impacts) everything that is on the surface of the Earth, including people. Millimeters of mercury (hereinafter referred to as mmHg) is a unit of measurement for blood pressure.

The following types of blood pressure are distinguished:

• Intracardiac or cardiac , which occurs in the cavities of the heart during its rhythmic contraction. For each part of the heart, separate normative indicators have been established, which vary depending on the cardiac cycle, as well as on the physiological characteristics of the body.
• Central venous (abbreviated as CVP), i.e. blood pressure of the right atrium, which is directly related to the amount of venous blood returned to the heart. CVP indicators are of utmost importance for diagnosing certain diseases.
• Capillary is a quantity that characterizes the level of fluid pressure in capillaries and depending on the curvature of the surface and its tension.
• Blood pressure – this is the first and, perhaps, the most significant factor, by studying which a specialist makes a conclusion about whether the body’s circulatory system is functioning normally or whether there are deviations. The value of blood pressure indicates the volume of blood that the heart pumps in a certain unit of time. In addition, this physiological parameter characterizes the resistance of the vascular bed.

Since it is the heart that is the driving force (a kind of pump) of blood in the human body, the highest blood pressure levels are recorded at the blood outlet from the heart, namely from its left stomach. When blood enters the arteries, the pressure level becomes lower, in the capillaries it decreases even more, and it becomes minimal in the veins, as well as at the entrance to the heart, i.e. in the right atrium.

Three main indicators of blood pressure are taken into account:

• heart rate (abbreviated heart rate) or human pulse;
• systolic , i.e. upper pressure;
• diastolic , i.e. lower.

What does a person's upper and lower blood pressure mean?

Upper and lower pressure indicators - what are they and what do they influence? When the right and left ventricles of the heart contract (i.e., the process of heartbeat occurs), blood is pushed out in the systole phase (the stage of the heart muscle) into the aorta.

The indicator in this phase is called systolic and is written first, i.e. is essentially the first number. For this reason, systolic pressure is called upper. This value is influenced by vascular resistance, as well as the frequency and strength of heart contractions.

In the diastole phase, i.e. in the interval between contractions (systole phase), when the heart is in a relaxed state and filled with blood, the value of diastolic or lower blood pressure is recorded. This value depends solely on vascular resistance.

Let's summarize all of the above using a simple example. It is known that 120/70 or 120/80 are the optimal blood pressure values ​​for a healthy person (“like astronauts”), where the first number 120 is the upper or systolic pressure, and 70 or 80 is the diastolic or lower pressure.

Let's be honest, while we are young and healthy, we rarely worry about our blood pressure levels. We feel good and therefore there is no reason to worry. However, the human body ages and wears out. Unfortunately, this is a completely natural process from a physiological point of view, affecting not only the appearance of a person’s skin, but also all of his internal organs and systems, including blood pressure.

So, what should normal blood pressure be in an adult and in children? How does age affect blood pressure? And at what age should you start monitoring this vital indicator?

To begin with, it should be noted that such an indicator as blood pressure actually depends on many individual factors (mental-emotional state of a person, time of day, taking certain medications, food or drinks, and so on).

Modern doctors are wary of all previously compiled tables with average blood pressure levels based on the patient’s age. The thing is that the latest research speaks in favor of an individual approach in each specific case. As a general rule, normal blood pressure in an adult of any age, no matter in men or women, should not exceed a threshold of 140/90 mm Hg. Art.

This means that if a person is 30 years old or at 50-60 years old the indicators are 130/80, then he does not have problems with the functioning of the heart. If the upper or systolic pressure exceeds 140/90 mm Hg, then the person is diagnosed. Drug treatment is carried out when the patient’s blood pressure “goes off scale” beyond 160/90 mmHg.

When blood pressure is elevated, a person experiences the following symptoms:

• increased fatigue;
• swelling of the legs;
• vision problems;
• decreased performance;

According to statistics, high upper blood pressure is most common in women, and low blood pressure is most common in older people of both sexes or in men. When the lower or diastolic blood pressure drops below 110/65 mm Hg, irreversible changes in internal organs and tissues occur, as blood supply deteriorates, and, consequently, oxygen saturation of the body.

If your blood pressure remains at 80 to 50 mm Hg, then you should immediately seek help from a specialist. Low lower blood pressure leads to oxygen starvation of the brain, which negatively affects the entire human body as a whole. This condition is as dangerous as high blood pressure. It is believed that the normal diastolic blood pressure of a person aged 60 years and older should not be more than 85-89 mmHg. Art.

Otherwise, it develops hypotension or . With low blood pressure, symptoms such as:

• darkening of the eyes;
• lethargy;
• increased fatigue;
• photosensitivity , as well as discomfort from loud sounds;
• feeling and coldness in the extremities.

Causes of low blood pressure may include:

• stressful situations;
• weather conditions, for example, stuffiness or sweltering heat;
• fatigue due to high loads;
• chronic lack of sleep;
• allergic reaction;
• certain medications, such as heart medications or pain medications, or antispasmodics .

However, there are examples where people live quietly throughout their lives with a lower blood pressure of 50 mmHg. Art. and, for example, former athletes whose heart muscles are hypertrophied due to constant physical activity feel great. That is why each individual person may have his own normal blood pressure readings, at which he feels great and lives a full life.

High diastolic pressure indicates the presence of diseases of the kidneys, thyroid gland or adrenal glands.

An increase in blood pressure can be caused by the following reasons:

• overweight;
• stress;
• and some other diseases ;
• smoking and other bad habits;
• unbalanced diet;
• sedentary lifestyle;
• weather changes.

Another important point regarding human blood pressure. To correctly determine all three indicators (upper, lower pressure and pulse), you need to follow simple measurement rules. Firstly, the optimal time to measure blood pressure is in the morning. Moreover, it is better to place the tonometer at the level of the heart, so the measurement will be the most accurate.

Secondly, the pressure may “jump” due to a sudden change in the person’s body posture. That is why you need to measure it after waking up, without getting out of bed. The arm with the tonometer cuff should be horizontal and motionless. Otherwise, the indicators produced by the device will have an error.

It is noteworthy that the difference between the indicators on both hands should not be more than 5 mm. The ideal situation is when the data does not differ depending on whether the pressure was measured on the right or left hand. If the indicators differ by 10 mm, then the risk of developing is most likely high, and a difference of 15-20 mm indicates anomalies in the development of blood vessels or theirs.

What are the blood pressure standards for a person, table

Let us repeat once again that the table below with blood pressure norms by age is just reference material. Blood pressure is not a constant value and can fluctuate depending on many factors.

Pressure rate table:

In addition, in some categories of patients, for example, pregnant women , whose body, including the circulatory system, undergoes a number of changes during the period of bearing a child, the indicators may differ, and this will not be considered a dangerous deviation. However, as a guide, these blood pressure norms for adults can be useful for comparing your indicators with average numbers.

Table of blood pressure in children by age

Let's talk more about children's blood pressure. To begin with, it should be noted that in medicine, separate norms for blood pressure have been established for children from 0 to 10 years old and for adolescents, i.e. from 11 years and older. This is due, first of all, to the structure of the child’s heart at different ages, as well as to some changes in hormonal levels that occur during puberty.

It is important to emphasize that children’s blood pressure will be higher the older the child is; this is due to the greater elasticity of blood vessels in newborns and preschool children. However, with age, not only the elasticity of blood vessels changes, but also other parameters of the cardiovascular system, for example, the width of the lumen of veins and arteries, the area of ​​the capillary network, and so on, which also affects blood pressure.

In addition, blood pressure indicators are influenced not only by the characteristics of the cardiovascular system (the structure and boundaries of the heart in children, the elasticity of blood vessels), but also by the presence of congenital developmental pathologies () and the state of the nervous system.

Normal blood pressure for people of different ages:

As can be seen from the table, the norm for newborn children (60-96 per 40-50 mmHg) is considered to be low blood pressure compared to older age. This is due to a dense network of capillaries and high vascular elasticity.

By the end of the first year of a child’s life, the indicators (90-112 by 50-74 mmHg) increase noticeably, due to the development of the cardiovascular system (the tone of the vascular walls increases) and the whole organism as a whole. However, after a year, the growth of indicators slows down significantly and blood pressure is considered normal at a level of 100-112 at 60-74 mm Hg. These indicators gradually increase by 5 years to 100-116 by 60-76 mmHg.

Many parents of younger schoolchildren worry about what normal blood pressure is for a child aged 9 years and older. When a child goes to school, his life changes dramatically - there are more loads and responsibilities, and less free time. Therefore, the child’s body reacts differently to such a rapid change in usual life.

In principle, blood pressure indicators in children 6-9 years old differ slightly from the previous age period, only their maximum permissible limits expand (100-122 by 60-78 mm Hg). Pediatricians warn parents that at this age, children's blood pressure may deviate from the norm due to increased physical and psycho-emotional stress associated with entering school.

There is no reason to worry if the child is still feeling well. However, if you notice that your little schoolchild is too tired, often complains of headaches, is lethargic and in no mood, then this is a reason to be wary and check your blood pressure readings.

Normal blood pressure in a teenager

According to the table, blood pressure is normal in children 10-16 years old, if its levels do not exceed 110-136 per 70-86 mmHg. It is believed that at the age of 12 the so-called “ awkward age" Many parents are afraid of this period, since a child from an affectionate and obedient baby under the influence of hormones can turn into an emotionally unstable, touchy and rebellious teenager.

Unfortunately, this period is dangerous not only for sudden changes in mood, but also for the changes that occur in the child’s body. Hormones that are produced in larger quantities affect all vital human systems, including the cardiovascular system.

Therefore, pressure indicators during adolescence may deviate slightly from the above norms. The key word in this phrase is insignificant. This means that if a teenager feels unwell and has symptoms of high or low blood pressure, he should urgently contact a specialist who will examine the child and prescribe appropriate treatment.

A healthy body can adjust itself and prepare for adult life. At 13-15 years old, blood pressure will stop “jumping” and return to normal. However, in the presence of deviations and certain diseases, medical intervention and drug adjustment are required.

High blood pressure may be a symptom of:

• arterial hypertension (140/90 mmHg), which without appropriate treatment can lead to severe hypertensive crisis ;
• symptomatic hypertension , which is characteristic of renal vascular diseases and adrenal tumors;
• vegetative-vascular dystonia , a disease characterized by surges in blood pressure within the range of 140/90 mmHg;
• lower blood pressure may increase due to pathologies in the kidneys ( , , atherosclerosis , developmental abnormalities );
• upper blood pressure increases due to defects in the development of the cardiovascular system, diseases of the thyroid gland, as well as in patients anemia .

If blood pressure is low, then there is a risk of developing:

• hypotension ;
• vegetative-vascular dystonia ;
• anemia ;
• myocardiopathy ;
• adrenal insufficiency ;
• diseases of the hypothalamic-pituitary system.

Controlling your blood pressure levels is really very important, and not only at 40 or after fifty. A tonometer, like a thermometer, should be in the home medicine cabinet of everyone who wants to live a healthy and fulfilling life. Spending five minutes of your time on a simple procedure for measuring blood pressure is actually not difficult, and your body will thank you very much for it.

What is pulse pressure

As we mentioned above, in addition to systolic and diastolic blood pressure, a person’s pulse is considered an important indicator for assessing heart function. What is it pulse pressure and what does this indicator reflect?

So, it is known that the normal pressure of a healthy person should be within 120/80, where the first number is the upper pressure, and the second is the lower.

So here it is pulse pressure is the difference between the indicators systolic And diastolic pressure , i.e. top and bottom.

Normal pulse pressure is 40 mmHg. Thanks to this indicator, the doctor can draw a conclusion about the condition of the patient’s blood vessels, and also determine:

• degree of wear and tear of arterial walls;
• patency of the vascular bed and their elasticity;
• the condition of the myocardium, as well as the aortic valves;
• development stenosis , , as well as inflammatory processes.

It is important to note that the norm is considered pulse pressure equal to 35 mm Hg. plus or minus 10 points, and the ideal is 40 mmHg. The value of pulse pressure varies depending on the age of the person, as well as on his state of health. In addition, other factors, such as weather conditions or psycho-emotional state, also influence the value of pulse pressure.

Low pulse pressure (less than 30 mm Hg), at which a person may lose consciousness, feel severe weakness, headaches , And dizziness talks about development:

• vegetative-vascular dystonia ;
• aortic stenosis ;
• hypovolemic shock ;
• anemia ;
• heart sclerosis ;
• myocardial inflammation;
• ischemic kidney disease .

Low pulse pressure - this is a kind of signal from the body that the heart is not working correctly, namely, it is weakly “pumping” blood, which leads to oxygen starvation of our organs and tissues. Of course, there is no reason to panic if the drop in this indicator was isolated, however, when this becomes a frequent occurrence, you need to urgently take action and seek medical help.

High pulse pressure, as well as low, can be caused by both momentary deviations, for example, a stressful situation or increased physical activity, and the development of pathologies of the cardiovascular system.

Increased pulse pressure (more than 60 mmHg) is observed when:

• pathologies of the aortic valve;
• iron deficiency ;
• congenital heart defects ;
• coronary disease ;
• inflammation of the endocardium;
• feverish conditions;
• when the level increases.

Normal heart rate by age

Another important indicator of heart function is heart rate in adults, as well as in children. From a medical point of view, the pulse is an oscillation of the arterial walls, the frequency of which depends on the cardiac cycle. In simple terms, the pulse is the beat of the heart or heartbeat.

Pulse is one of the oldest biomarkers by which doctors determined the condition of a patient’s heart. Heart rate is measured in beats per minute and usually depends on the person’s age. In addition, other factors, such as the intensity of physical activity or a person’s mood, also affect the pulse.

Each person can measure his own heart rate; to do this, you just need to mark one minute on the clock and feel the pulse on your wrist. The heart works normally if a person has a rhythmic pulse, the frequency of which is 60-90 beats per minute.

Normal blood pressure and heart rate by age, table:

It is believed that the pulse of a healthy (i.e., without chronic diseases) person under the age of 50 should not exceed 70 beats per minute on average. However, there are some nuances, for example, in women after 40 years of age, when it begins, it can be observed, i.e. increased heart rate and this will be a variant of the norm.

The thing is that when it occurs, the hormonal background of the female body changes. Fluctuations in such a hormone affect not only heart rate, but also indicators blood pressure , which may also deviate from standard values.

Therefore, the pulse of a woman at 30 years old and after 50 will differ not only because of her age, but also because of the characteristics of the reproductive system. All representatives of the fair sex should take this into account in order to worry about their health in advance and be aware of upcoming changes.

Heart rate can change not only due to any ailments, but also, for example, due to severe pain or intense physical activity, due to heat or in a stressful situation. In addition, the pulse directly depends on the time of day. At night, during sleep, its frequency decreases noticeably, and after waking up it increases.

When the heart rate is higher than normal, this indicates the development of a disease that is often caused by:

• malfunction of the nervous system;
• endocrine pathologies;
• congenital or acquired malformations of the cardiovascular system;
• malignant or benign neoplasms;
• infectious diseases.

During tachycardia may develop against the background anemia . At food poisoning in the background vomiting or severe, when the body is dehydrated, a sharp increase in heart rate may also occur. It is important to remember that a rapid heart rate may indicate the development of heart failure when tachycardia (heart rate more than 100 beats per minute) appears due to minor physical exertion.

Opposite tachycardia a phenomenon called bradycardia is a condition in which the heart rate drops below 60 beats per minute. Functional bradycardia (i.e. normal physiological state) is typical for people during sleep, as well as for professional athletes, whose body is subject to constant physical stress and whose autonomic heart system works differently than that of ordinary people.

Pathological, i.e. Bradycardia, dangerous for the human body, is recorded:

As can be seen from the above table of heart rate norms for children by age, heart rate indicators become lower as the child grows up. But with blood pressure indicators, the exact opposite picture is observed, since they, on the contrary, increase as they grow older.

Heart rate fluctuations in children may be due to:

Education: Graduated from Vitebsk State Medical University with a degree in Surgery. At the university he headed the Council of the Student Scientific Society. Advanced training in 2010 - in the specialty "Oncology" and in 2011 - in the specialty "Mammology, visual forms of oncology".

Experience: Worked in a general medical network for 3 years as a surgeon (Vitebsk Emergency Hospital, Liozno Central District Hospital) and part-time as a district oncologist and traumatologist. Work as a pharmaceutical representative for a year at the Rubicon company.

Presented 3 rationalization proposals on the topic “Optimization of antibiotic therapy depending on the species composition of microflora”, 2 works took prizes in the republican competition-review of student scientific works (categories 1 and 3).

Over the past ten years, arterial hypertension has become such a common disease that American, and after them European, cardiologists decided to revise the standards that had been in place since 2013 regarding human blood pressure (BP). This issue was raised at the ESC (European Society of Cardiology) conference, held on August 25-29, 2018 in Munich.

As a result, the conference decision lowered the level of recommended human pressure, and the norm for people under 65 years of age is now 120-129/80 mmHg. For other age categories, blood pressure standards have remained almost unchanged, but the range of permissible deviations has narrowed.

So, since 2018, in the countries of the European Union and the United States there has been a single norm of human blood pressure for adults under the age of 65 years. mmHg is considered ideal, but given the instability and dependence of this health marker on many influencing factors, doctors allow deviations within a certain range of pressure values, which is considered normal for healthy people.

Reference blood pressure values ​​by year

Reference, or averaged within the normal range, blood pressure values ​​have long been considered 110-139 for systolic and 60-89 for diastolic indicators. Therefore, antihypertensive therapy was considered successful if a person’s blood pressure could be kept at mmHg. Today, target values ​​and normal limits have been reduced.

Permissible deviations

The physiological characteristics of the body can be expressed, among other things, by the individual limits of normal blood pressure. Therefore, when correlating blood pressure measurements with the norm, some deviations are allowed.

1. The lower limit of normal pressure is considered to be (+/- 10).
2. The upper limit of normal has dropped to 130 mmHg since 2018.
3. With regard to diastolic pressure, the maximum permissible normal value became 80 mmHg.
4. The minimum acceptable diastolic is 60 (+/- 5) mm.

The main criterion for the norm remains a person’s well-being. For example, in a person with physiological hypotension, a blood pressure of 130/80 may cause headaches and chest discomfort.

Another example is that if a hypertensive patient does not tolerate a drop in blood pressure to the specified norms, the target values ​​of antihypertensive therapy can be individually increased for him. The decision to review the dosages of antihypertensive drugs is made by the attending physician.

Summary table of blood pressure norms by age

Due to the instability of blood pressure, it is difficult to establish clear boundaries of normal blood pressure by year, enclosed in a table. Therefore, the following data should be taken as guide values.

Table of blood pressure norms for adults and children

Today's diastolic pressure standards for older people seem difficult to achieve, but it is precisely these figures that cardiologists around the world consider optimal in terms of preventing vascular accidents.

Blood pressure depends on many factors

Normal for men

In the table of blood pressure norms, you can see that the blood pressure values ​​​​for men and women do not have striking differences. Various factors influence the tone of blood vessels in men:

• emotional and physical stress;
• taking certain medications, caffeinated drinks, alcohol;
• stress, activities;
• nutritional features and others.

Doctors noticed that the most important factor in the status of a man’s vascular system is the hereditary predisposition transmitted by the mother. Most cases of congenital or tendency to increase blood pressure in men are explained by this.

A man may not notice blood pressure deviations from normal values ​​in one direction or another for years, which is sometimes interpreted as an individual blood pressure norm. But it should not exceed the threshold values ​​- 130/80 mmHg.

Individuals who engage in sports or regular physical training are prone to low blood pressure. At rest, their blood pressure can drop to critical levels for healthy people, but in this case we are talking about the individual norm.

For women

Blood pressure in women is influenced by physiological factors such as menstruation, pregnancy, and breastfeeding. The intervention of external or pathological factors can lead to both a decrease in blood pressure and an increase in blood pressure. Normal for women is considered to be the one shown in the table by year - no less than 100/60 and no more than 130/80 mmHg.

During the perinatal period, pressure fluctuations in women may be more noticeable and require attention, as they affect intrauterine development. This is discussed in more detail below.

For children and teenagers

To correlate indicators and norms of blood pressure in children, doctors use a table, as well as formulas for calculating the proper values ​​by age.

For babies aged 1-12 months, the normal systolic pressure is calculated as follows:

• 76 + 2n, where unknown = number of months;
• maximum systolic: 105 + 2n, where n is the number of months (up to 1 year) or years.

Diastolic blood pressure is calculated for children of this age using the formula: 1/2 of the upper systolic limit. For example, let's calculate the pressure for a 6-month-old baby:

• SBP = 76 + 2x6 = 88 mmHg;
• DBP = (105 + 2x6): 2 = 53 mmHg.

For ages over 1 year, different formulas apply:

• 90 + 2n – for systolic pressure, where n is the number of years;
• 60 + n – for diastolic pressure.

For a child aged 11 years, the pressure calculation is as follows:

• SBP = 90 + 2x11 = 112 mmHg;
• DBP = 60 + 11 = 71 mm Hg.

The formulas provide only approximate data on pressure values, without taking into account the individual characteristics or genetic predisposition of the child.

Changes in blood pressure in a child

Table of norms for heart rate, respiratory rate and blood pressure in children

In addition to blood pressure, an important biological marker of a person is the frequency of respiratory movements, calculated within 1 minute, and abbreviated as respiratory rate.

Respiration rate (inhalations and exhalations) is measured when assessing the physical condition of a patient with diseases of the respiratory system and others. In this case, the type of breathing is usually established:

• breast (female);
• abdominal (male);
• mixed (children).

The type of breathing is determined by the number of breaths counted per minute:

• slow – bradypnea;
• accelerated – tachypnea;
• absence (delay) – apnea.

For human respiratory movements, age standards are also provided:

• in an adult 16-20 per minute. at rest;
• 12-16 per minute – during sleep;
• in newborns - 30-60 per minute.

The following table provides more detailed data on the most important parameters of the body of adults and children.

Table of blood pressure, heart rate and respiratory rate in children and adults

As you can see from the table, in children, blood pressure increases with age, and heart rate and respiratory rate decrease.

Optimal blood pressure in pregnant women by trimester

In women carrying a child, pressure fluctuations are inevitable due to hormonal changes and the body’s need to “pump” blood for two. What level of blood pressure in pregnant women can be considered normal depends on the woman’s initial blood pressure (before pregnancy).

In the first trimester, most women experience a decrease in indicators caused by hormonal changes.

From the 2nd trimester until childbirth, some pregnant women develop gestosis - high blood pressure, which threatens the normal intrauterine development of the baby. Fortunately, such situations are mostly exceptional.

It makes no sense to compile a table of blood pressure norms, since the ideal indicator for pregnant women is considered to be the same pressure that serves as a guideline for adults - 120/80 mm Hg.

Deviations from the norm in the upward direction in most pregnant women are noted by no more than 10-15 mm Hg.

Only a gynecologist monitoring the course of pregnancy can assess the danger of the condition, taking into account the patient’s medical history.

Features of blood pressure in the elderly

The blood vessels of older people (over 65 years of age) undergo changes leading to a physiological loss of their elasticity.

1. The endothelium lining the inner surface of the vessels undergoes sclerotization.
2. Smooth muscle cells become exposed and atrophy over time.
3. The outer lining of the arteries thickens, becoming coarser due to the thickening of elastic and collagen fibers, followed by fibrosis.

All this leads to an increase in the rigidity of the arterial walls and their inability to dilate (expand), which is why the blood pressure in the vessels of elderly people exceeds the norms of adults. A common phenomenon for this age is “jumps” in pressure up and down, as well as an isolated increase in systolic index (ISAG).

The normal blood pressure for older people is considered to be from 110 to 139 on the upper level and from 70 to 80 mm on the lower level.

Useful video

Look what the doctor says about the norms of a person’s blood pressure by age:

Conclusion

1. The normal blood pressure for an adult is considered to be 110-130/70-80 mmHg. for ages 20-65 years.
2. In some cases, due to heredity or other factors, values ​​of 100/60 mmHg are considered the individual norm.
3. The blood pressure of pregnant women can normally fluctuate by 10-15 mm Hg; more serious deviations from the norm are dangerous for intrauterine development.