home Warm floor What is a trimester of pregnancy? Trimesters - what are they? How many months and weeks is a trimester? Obstetric pregnancy calendar: what are trimesters

What is a trimester of pregnancy? Trimesters - what are they? How many months and weeks is a trimester? Obstetric pregnancy calendar: what are trimesters

Pregnancy is a time when a woman discovers a new world for herself. In addition to new sensations and anxieties, expectant mothers are faced with previously unknown concepts and terms. Many women know that the period of bearing a baby is divided into trimesters. However, it is not clear to everyone what this means and why pregnancy is conventionally divided into parts.

Pregnancy trimester – what is it, how long does each trimester last?

The obstetric term for bearing a child is 40 weeks, or 280 days, which is approximately equal to 9 calendar months. At this time, the woman’s body undergoes changes, which take on different characters in different periods.

Trimester is one of the 3 stages of pregnancy. Pregnancy trimesters are measured by week. The first trimester lasts 13 weeks. The countdown of the first trimester of pregnancy begins from the first day of the last menstruation. The fertilization process itself takes place at 1–2 weeks of pregnancy.

The second trimester begins from the 14th week. From the 28th week of pregnancy, the third period of gestation begins.

Beginning: first trimester

The first three months of pregnancy are called the most responsible. At this time the body expectant mother adapts to the fact that a new person is growing inside him. Most women at the beginning of the term do not suspect that they are pregnant and continue to lead their usual lifestyle. However, many mothers begin to feel changes already from the 4th week. During the 1st trimester, the baby's systems and organs are formed.

Signs of pregnancy in the first weeks

In most cases, women assume that they are pregnant in the absence of regular menstruation. Expectant mothers also experience the onset of pregnancy through ailments that were previously uncharacteristic for them.

Different women may experience different sensations. However, there are signs by which one thinks about the probable interesting position most expectant mothers:

nausea in the morning and at other times of the day;
lack or increased appetite;
change in gastronomic preferences;
frequent urge to urination;
swelling of the mammary glands;
drowsiness;
sudden change of mood;
diarrhea or constipation;
breast tenderness or pain in the breast.

How does the baby develop?

Fertilization of the egg occurs within 14 days after ovulation. After the meeting of the egg and sperm, a zygote is formed, which reaches the uterus on the 5th–6th day and is implanted into it. As the zygote moves toward its attachment site, it continually divides.

After the embryo penetrates the uterus, the formation of the placenta and the tube through which the baby will feed (umbilical cord) begins. At about 4 weeks of pregnancy, the embryo looks like a tube with a slight thickening at the end. Its size reaches 1.5–2 mm. During this period, the heart is formed, the brain and spinal cord are formed.

During weeks 5–8 of pregnancy, the embryo grows rapidly. His brain is divided into sections, a respiratory system, gastrointestinal organs are formed, blood vessels appear circulatory system. At week 6, the heart divides into chambers and begins to pump blood. By week 7, limbs are formed, hands and fingers form on the arms.

By the end of the second month of pregnancy, the baby reaches 25 mm in length. The nose and mouth are already visible on his face, and his kidneys are starting to work. In the photo below you can see the embryo at 8 weeks.

At week 9, the embryo becomes a fetus (we recommend reading: external signs of pregnancy at week 9). By this time, he has completed the laying of all internal organs. Formed muscular system and spine. The baby can move his arms and legs.

During the 10th week, the baby's buttocks begin to form. It can move inside the uterus. By the end of the first trimester, the fetus begins to develop future teeth, it can move its fingers, the visual organ improves, and the ears stand out. The child's weight is approximately 7 grams and his height is 8 cm.

What's happening to mom?

During the initial 14 weeks, the mother's body undergoes changes. It begins to intensively produce hormones that contribute to the development of the baby and the maintenance of pregnancy; the internal organs are rebuilt to ensure the vital functions of the mother and the growing baby. The following processes occur:

Immunity decreases so that the body does not reject the fetus.
The uterus is enlarged.
The condition of the mammary glands changes. The hormones produced prepare the mother for future lactation.
Blood volume increases. To supply the baby with oxygen it is necessary large quantity red blood cells
The vessels of the uterus and pelvis dilate. This is necessary for blood supply to the fetus and relaxation of the uterine muscles.
Blood pressure decreases.

Mood changes, weakness and nausea are explained by changes in the body hormonal background. Unusual eating habits appear due to the fact that women subconsciously look for a way to enrich their bodies with the substances necessary for the formation of a child.

Early examinations

Doctors recommend registering before 12 weeks of pregnancy. Early diagnosis allows timely recognition of pathologies that can impede the normal course of pregnancy and the development of the baby. Early examination includes:

gynecological examination;
visiting an ENT specialist, dentist, ophthalmologist, therapist;
interviewing the expectant mother and collecting anamnesis;
fixation of weight and height;
carrying out laboratory tests.

The expectant mother needs to undergo the following tests:

general blood analysis;
blood test for hCG;
general urine analysis;
analysis of biomaterial for sugar;
establishment of the Rh factor;
blood for TORCH infections;
vaginal smear to determine microflora and inflammatory processes;
Ultrasound at 10–12 weeks.

Dangers of the first trimester

Many women try to hide their new condition during the first 12 weeks of pregnancy. Many people consider the reluctance to tell others about a joyful event a superstition, but the expectant mother’s fear of losing her child early has a medical basis.

In the first trimester, there is a possibility of rejection of the fertilized egg. Miscarriage can be caused by:

strong emotional and physical stress;
poor nutrition;
smoking and alcohol;
mother's illness;
genetic pathologies of the fetus;
insufficient production of progesterone;
Rhesus conflict between mother and child.

In order for the pregnancy to develop safely, a woman needs to monitor her health and nutrition, follow the recommendations of her gynecologist, and undergo the necessary examinations on time. During pregnancy, experts recommend staying away from stress and taking frequent walks. fresh air. You should immediately consult a doctor if the following symptoms occur:

pain in the lower abdomen;
bleeding from the vagina;
high body temperature.

Features of the second trimester

The second trimester of pregnancy is considered the calmest period. By this time, the mother’s condition has stabilized and the process of forming the unborn baby ends. It is in the second period of pregnancy that most women begin to feel the joy of expecting a child and a surge of strength. The baby in the womb continues to develop. For its growth, the body requires more and more resources.

Formation and growth of the baby

In the 2nd trimester, most of the child’s organs and systems are already functioning. On at this stage they are improving. By the second period of gestation, the fetus begins to receive full nutrition through the umbilical cord and placenta. The table describes the features of the child’s development by week and its expected parameters during this period.

A week	Height from head to tailbone, cm	Weight, g	Development
14	9	25	The chin and cheeks appear, the genitals are formed, and urine is released.
15	10	75	Eyelids and eyebrows differ, ears take on their usual shape.
16	11	100	Facial muscles are improved.
17	12	140	Your own immunity begins to work. Vernix lubrication and subcutaneous fat appear.
18	14	up to 200	The child begins to respond to external sounds.
19	19	240	Sex hormones are produced.
20	22	270	The skin becomes less transparent.
21	27	300	Taste perception appears.
22	28	400	The baby plays with the umbilical cord, the digestive system is trained.
23	29	500	Movements become conscious.
24	31	530	The lungs produce the substance necessary for breathing.
25	34	700	Improves bone marrow.
26	35	750–850	New hormones begin to be produced.
27	36	900	Subcutaneous fat accumulates.

How does the woman feel?

In the second trimester, a woman’s toxicosis goes away and balances out. emotional condition. From 16 to 20 weeks, expectant mothers begin to feel the baby's movements. The belly continues to grow, and the pressure of the uterus on the internal organs increases.

A woman gains weight weekly. The main reasons for the increase are the growth of the baby and an increase in the amount of amniotic fluid. The expectant mother may be concerned about the following phenomena:

Back pain. By the end of the sixth month, many women begin to experience back pain due to increased stress on the spine.
Constipation. Intestinal dysfunction is associated with increased stress on internal organs.
Haemorrhoids. It is a consequence of changes in the functioning of the vascular system and rapid weight gain, frequent constipation.
Frequent urination. Associated with pressure from the uterus on the bladder.

Tests and ultrasound

During this period, the woman must visit the doctor monthly and donate blood and urine for a general analysis. The doctor also prescribes a biochemical blood test, and at 16–21 weeks, tests are done to identify genetic pathologies and determine hormone levels, and a repeat ultrasound.

During the examination, the specialist examines the size of the fetus and compares it with the norm. Ultrasound also allows you to assess the condition of the placenta and see the level of development of the child’s internal organs. Future parents can be told the gender of the baby.

Childbirth is coming soon!

The last stage of pregnancy is the most exciting for the expectant mother. In addition to new sensations, the woman develops fear of childbirth and excitement about the upcoming meeting with the child. Pregnant women are prescribed new examinations. Some women last weeks before childbirth is carried out in the hospital due to late toxicosis. However, many expectant mothers are constantly surrounded by family.

Baby development and behavior

In the last trimester, the baby's lungs prepare for breathing, and the brain improves the necessary life reflexes. It is believed that a child born after 28 weeks is fully viable with proper care. However, early birth is highly undesirable. The table describes the features of the baby's development in the last months of gestation.

Week of pregnancy	Height, cm	Weight, g	Developmental features and behavior
29	38	1100	Actively pushing. All organs and systems are working.
30	39	1300	The amount of protective lubricant in the lungs increases. Limbs lengthen, bones become stronger.
31	40	1500	A sleep and wakefulness pattern is developed. The color of the iris is formed.
32	42	1750	The baby begins to suck his thumb.
33	43	2000	The baby is less active due to the lack of space in the uterus.
34	44	2500	Hair is actively growing.
35	45	2700	The amount of subcutaneous fat increases. The nails on the fingers are different.
36	up to 48	up to 3000	The skin is smoothed and brightened. Organs are prepared for life outside the womb.
37	49	3000–3100	The lungs are completely ready for birth. The skeletal system becomes stronger.
38	50	3100	The baby is completely ready for birth. It sinks into the pelvis.
39	from 50	from 3100

Mom's feelings, risks and examinations

In the 3rd trimester, the mother feels active movements of the baby, which subside in the last month of pregnancy. The belly is getting bigger. Due to the increasing load on the kidneys, edema may appear. A pregnant woman may be concerned about the following:

dyspnea;
heartburn;
lower back pain;
constipation;
frequent urination.

At the end of pregnancy, many women experience so-called false contractions. Unlike the real ones, they quickly subside. In the last trimester there is a risk of premature birth. They can happen due to the following factors:

chronic diseases of the mother;
gestosis;
high blood pressure;
late or early pregnancy;
improper formation of the fetus;
lack of nutrition;
emotional stress;
genital tract infections;
intrauterine infection of the fetus;
lack of hormones.

To monitor the condition of mother and child, doctors prescribe blood and urine tests. The mother is retested for TORCH infection. An ultrasound at 34 weeks allows you to assess the condition of the placenta and find out how much time is left before birth.

How to prepare for childbirth?

There are many tips for preparing for childbirth. Women attend special courses and learn how to breathing exercises, preparing things for themselves and the future baby. However, it is necessary to take into account that every woman’s body is individual.

Knowing what happens to the baby in the belly in each trimester and being aware of the characteristics of her body at a particular stage of pregnancy, the expectant mother will be able to prevent complications during childbirth and spend all 9 months in a positive mood.

Trimesters of pregnancy (by weeks, doctors and gynecologists decided to classify the process of a woman carrying a child in the last century) is the result of a conditional division of 9 months of fetal formation in the mother’s womb into periods, each of which lasts 3 months.

During all 3 trimesters, not only the physical development of the little person occurs, but also the constant transformation of the pregnant woman’s body. To make it easier to monitor the condition of expectant mothers, gynecologists have developed a number of standard indicators by which they assess the health of a woman and her child during a scheduled weekly examination.

The trimesters of pregnancy by week are shown in this table.

Such assessment factors include:

fetal weight (determined by ultrasound);
body weight of a pregnant woman;
child's body length;
the volume of the expectant mother's abdomen;
the woman has swelling, pain of various types, insomnia, and so on;
results of general urine and blood tests;
visual examination of the condition of the cervix (in the absence of complaints from the expectant mother, performed by gynecologists only in the first and third trimester);
the heart rate of a small person in the womb;
blood pressure of a pregnant girl.

Thanks to generally accepted indicators, based on deviations from them in each trimester, doctors can timely diagnose the onset of pathology and prevent it without causing harm to the health of the mother and child. The most dangerous is the first trimester.

It is during this period that there is a high risk of sudden termination of pregnancy due to the inattention of the expectant mother to her body (pregnant women do not always find out about their situation from the first days, they continue to lead a normal lifestyle, lifting weights, not devoting the proper amount of time to sleep, neglecting the principles proper nutrition and so on).

Dividing pregnancy into trimesters, months, weeks

During these few weeks, ovulation occurs, fertilization of the egg, as well as its “implantation” into the uterine wall, followed by laying the foundation for the further construction of the human body. The first trimester lasts until 12-13 weeks.

If no termination of pregnancy occurs during this period, then, provided there are no pathologies in the woman’s health, sudden loss of the child before the expected date of birth is unlikely. From the 13th week the second trimester begins, which, by analogy with the first, has a duration of 3 months. At this time, the child is actively gaining weight and increasing in height, acquiring a human appearance.

At the second stage of pregnancy, a woman begins to feel the first movements of her baby, and also, in some cases, after a routine ultrasound examination, she can already find out his gender (in the second trimester, the child’s reproductive system is already fully formed, which allows the ultrasound doctor to visually guess who the woman is expecting - boy or girl).

From the 28th week of pregnancy the third trimester begins.

At the final stage of bearing a child, a woman usually begins to experience discomfort associated with a sharp increase in the load on her body (the weight of the child at the period in question already exceeds 2 kg, and the volume of blood required for normal nutrition of the placenta, which nourishes the baby’s vital systems inside the womb, extremely large).

To simplify the perception of information about dividing pregnancy into periods, gynecologists recommend that expectant mothers use a generally accepted table.

Table:

Trimester	Months	weeks
1	first; second; third.	from 1 to 4; from 5 to 8; from 9 to 12-13.
2	fourth; fifth; sixth.	from 14 to 17; from 18 to 21; from 22 to 27.
3	seventh; eighth; ninth.	from 28 to 31; from 32 to 36; from 37 to 40.

Changes in the body of the expectant mother and child during each trimester

The trimesters of pregnancy (week by week the child not only increases in size and weight, but also acquires new skills necessary for subsequent life outside the mother’s womb) determine the condition of both the fetus itself and the pregnant woman.

Understanding what changes in the body are coming during the next trimester, expectant mother will be able to mentally prepare himself for possible difficulties and make every effort to prevent discomfort.

Trimester	Changes in the body of a pregnant woman	Changes in the child's body
1	the appearance of signs of toxicosis, most often manifested already at 5-7 weeks of pregnancy (nausea, vomiting, changes in taste preferences; dizziness); increase in breast size; increased sensitivity of the mammary glands (in some cases, at this stage of pregnancy, pregnant women complain of pain and a feeling of fullness in the breasts); increased urge to urinate (the uterus with the “implanted” fetus puts pressure on the bladder); drowsiness; excessive fatigue; excessive emotionality caused by hormonal changes.	formation of the neural tube (the basis for the future central nervous system); the heart muscle begins to function; the beginning of the formation of the spinal column, the brain and its hemispheres, in particular; laying the foundations for the future formation of eyes, ears, limbs, organs gastrointestinal tract and thyroid gland; formation of genital organs, fingers on the upper and lower extremities; the beginning of the production of hormones by the endocrine system, as well as the formation of the rudiments of baby teeth in the gums; the baby begins to move inside the mother's womb.
2	increase in abdominal size; possible occurrence of pain in the lumbar and thoracic spine; discomfort in the hip joints; the likelihood of developing varicose veins (due to rapidly growing weight).	increase in height and body weight; completion of the formation of the reproductive and skeletal systems of the child’s body; active development of muscles and brain; increase in physical activity.
3	increasing the size of the uterus to its maximum size; difficulty breathing associated with increased pressure from below on the organs of the respiratory system; sleep disorders; frequent urge to urinate; excessive fatigue; the occurrence of “false contractions” (a kind of preparation of the uterus for the upcoming labor).	final formation of all vital organs and systems of the body; improving the ability to perceive information through hearing and perform breathing movements; the appearance of taste perception; active hair growth on the head; the formation of lubricant throughout the body, designed to facilitate the baby’s passage through the birth canal during birth.

Fetal development by weeks and months

Keeping track of how the fetus is developing each month or week of pregnancy helps reduce the overall anxiety of the expectant mother, as well as strengthening her parental feelings towards her child.

First trimester

Table:

A week
1 — 2	Based on the fact that the beginning of pregnancy is considered to be the first day menstrual cycle, then the first two weeks of bearing a child are conditional, since actual conception has not yet occurred.
3	Fertilization of the egg occurs, as a result of which the color of the eyes and hair of the unborn child is determined at the genetic level. The egg begins its division and moves towards the uterus.
4 (end of 1 month of pregnancy)	The fertilized cell implants in the uterus and grows to the size of a poppy seed.
5	The embryo grows up to 2-3 mm in length, while acquiring two poles, where the lower and upper limbs will subsequently begin to form. 3 functional layers are formed, which are the basis for the further formation of the vital systems of the little person’s body. The neural tube appears.
6	Formation of the upper and lower limbs of the child and increased growth of the embryo.
7	Increasing the size of the embryo to the proportions of a black currant or raspberry. Division of the child's brain into 3 functional sections. Active formation of limbs and laying the foundations for the formation of ears and nose.
8 (end of 2 months of pregnancy)	Formation of external facial features, limbs and vital organs. Beginning of fetal motor activity.
9	Increasing the size of the embryo to the size of a plum tree fruit. Formation of the reproductive system of a small person.
10	Active brain development. The film membrane between the fingers of the upper and lower extremities disappears. Increasing the strength of the skeletal system.
11	Increase in fetal size and weight. The gradual acquisition by his body of a human proportional appearance.
12	The child grows to the size of a small orange. External genitalia are formed. Nail plates appear on the fingers and toes.
13 (end of 3 months of pregnancy and first trimester)	The child’s brain and visual organs are actively developing. The rudiments of baby teeth appear in the baby’s gums. Hair slowly begins to grow on the head.

Second trimester

Table:

A week	Fetal development at a specific stage of pregnancy
14	The endocrine system begins to produce hormones. The strength of the chest increases. As the upper palate completes its formation in the child’s mouth, he acquires a sucking reflex.
15	The production of specific proteins of a particular blood group begins. The emergence of skills to change facial expressions. Motor activity increases (the expectant mother most often does not yet feel the movements of the fetus).
16	Active weight gain occurs and mucous membranes are formed. If the fetus carried by a woman is a girl, then at week 16 the little person will begin to form her own eggs - the basis for the reproductive system.
17 (end of 4 months of pregnancy)	The first fat deposits appear under the baby’s skin. He is actively increasing his height and weight while continuing to practice high physical activity.
18	The emergence of the ability to perceive the world through the organs of hearing. The formation of an emotional connection between the little person and his parents begins (the child gets used to their voices, hears the mother’s heartbeat, and so on).
19	Molars begin to form under the rudiments of baby teeth. A special mucus appears on the child’s body, which promotes proper thermoregulation.
20	The final formation of the child's facial features. The emergence of taste perception.
21 (end of 5th month of pregnancy)	The skeletal system actively develops and the bone marrow begins to function.
22	Change in skin color (becomes whitish). Hairs on the face (in particular, eyebrows and eyelashes) are formed.
23	The brain and central nervous system are actively developing. Completion of the formation of vital organs.
24	The formation of the organs of visual perception is completed, despite the continued absence of pigment (colorless eyes). The child begins to practice various movements, thus studying his body.
25 (end of 6 months of pregnancy and 2 trimesters)	Maturation of the gastrointestinal tract and the formation of meconium in the intestines.

Third trimester

Table:

A week	Fetal development at a specific stage of pregnancy
26	The child develops his own daily routine, which does not depend on the time of wakefulness and rest of the expectant mother. The respiratory organs are actively forming, preparing to function outside the womb.
27	The child learns to open and close his eyes in response to bright light. The baby calms down and falls asleep when gently rocked (the pregnant woman at this time can be on public transport, walking or doing household chores). The amount of hormones produced increases.
28	Increase in height and weight.
29 (end of 7 months of pregnancy)	Active brain development. During sleep, a child begins to dream, he develops emotions - he learns to be scared and enjoy.
30	The child begins to actively convey to the mother his attitude towards external circumstances. For example, he may start kicking if a woman is near the source of noise.
31	The child increases in all parameters, while at the same time reducing his motor activity.
32	The fetus is positioned as it will lie in the mother's belly until birth, which determines the type of labor that will occur (natural birth or Caesarean section).
33 (end of 8 months of pregnancy)	The child begins to adapt to his mother’s daily routine, repeating periods of activity and rest after her.
34	Completion of the formation of the respiratory organs.
35	Significant increase in the child's weight. The lubricant on the body acquires a thicker consistency, which will help the little person pass through the birth canal less painfully.
36	The final stage of formation of the nervous and immune systems. Subcutaneous fat accumulates.
37	Completion of the formation of all systems and organs of the child’s body.
38 – 40 (end of 9 months of pregnancy)	With cephalic presentation, the baby's head drops into the pregnant woman's pelvis, which is a sign of the body's readiness for the upcoming birth.

A woman’s feelings as the fetus develops

The trimesters of pregnancy according to the weeks of child development determine not only the physical, but also the emotional state of the expectant mother. In the first trimester, a pregnant woman is overcome by manifestations of toxicosis (nausea, vomiting, dizziness). Most women lose a lot of weight in the first months and do not yet feel an emotional attachment to their child.

Due to hormonal changes in the body, they often cry, laugh for no reason, become more irritable and require increased attention.

As the fetus develops, by the second trimester, toxicosis ends, and the stomach becomes rounded and increases in size, which allows the woman to begin to enjoy her position. The psychological background is leveled out and an emotional connection with the little person in the stomach is born (usually it is especially intensified after the first mother feels the kicks of her baby).

In the third trimester, despite the re-emerging physical discomfort (swelling, insomnia, frequent urge to urinate), the expectant mother is stable in her emotions, looking forward to meeting the baby and enjoying her pregnancy. At this stage, girls usually attend a 3D ultrasound in order to take a photo of the child as a memory of the period it was in the womb.

Possible deviations

Pregnancy lays the foundation for the future health of the little person. Knowing what abnormalities can be identified in a specific week of fetal life, the expectant mother will be able to prevent their occurrence by adjusting her lifestyle at each trimester.

Most often doctors diagnose during pregnancy:

Down syndrome(chromosomal mutation leading to dementia and serious developmental delay in the child);
Patau syndrome(a genetic mutation, the owners of which rarely live longer than a year. It provokes deafness, mental retardation and a number of other serious pathologies);
heart disease(some of them are subject to surgical correction, others allow a person to live, forgetting about their existence);
pathologies of the development of limbs or vital organs(they are not congenital and arise at the stage of laying the foundations of the body systems during pregnancy).