In women of reproductive age, the uterus has the shape of a pear. It is stretched from top to bottom and slightly flattened in the direction from the abdomen to the back.
Its length is 8−9 cm, maximum width – about 5 cm, weight – about 50 g. The uterus is located in the center of the pelvis, between the bladder and rectum.
To understand how the uterus changes during pregnancy, you need to take a closer look at its structure. This organ consists of the neck, neck, body and bottom.
During pregnancy, they all vary greatly.
The narrow lower part of the uterus is called the cervix; it connects the body of the uterus and the vagina. In mature women, the neck is one third the length of the uterus (about 2 cm).
In the center of the neck passes the cervical canal, filled with mucus. A few days after fertilization, the mucous membrane of the neck acquires a bluish tint due to the abundance of blood vessels, which are beginning to be actively supplied with blood.
This is one of the signs that allow the doctor during the examination to suspect pregnancy.
Between the cervical canal and the uterus, there is an isthmus, or isthmus, the narrowest part of the uterus about 1 cm long. During pregnancy, the isthmus, together with the lower part of the uterus, forms the so-called lower uterine segment – the place where the presenting part (head or pelvis) of the future is located baby
If the pregnancy is normal, the cervix is dense to the touch and slightly tilted back, the cervical canal is closed. With the threat of abortion, the cervix shortens and softens, and the canal opens slightly. This can be seen during a gynecological examination, and an ultrasound helps to determine the exact length of the cervix.
Normally, on the 9th month of pregnancy, the cervix softens, indicating readiness for childbirth. Directly in front of them, it shortens to 1–1.5 cm. During labor, the cervix should open.
Full opening occurs when it opens up to 10 cm. This means that the path to the baby is open.
The readiness of the cervix for childbirth and the rate of disclosure are checked during the study before delivery and during childbirth. To find out if there is an infection, a smear is taken every 3 months for flora.
The uterus consists of three layers – endometrium, myometrium and perimetry. Endometrium is the inner mucous layer. It lines the uterus, is pierced with many blood vessels and is covered with ciliated epithelium.
The cilia move towards the uterus, helping to promote a fertilized egg when it selects a site for implantation. At the same time, preparing for the “adoption” of the embryo, the endometrium expands, and during pregnancy the uterine lining becomes a bed for the baby.
This layer is also rich in glands that produce mucus. It contains special substances that can kill harmful microorganisms.
In this way, the uterus protects the unborn child from the penetration of infections.
At the 4th week of pregnancy, the chorion, the outer germinal envelope, completely covering the embryo begins to grow into the endometrium. It provides nutrition and prenatal breathing of the future baby up to the formation of the placenta.
The shell is covered with fibers, in which there are many blood vessels. The villi grow into the uterine mucosa, forming a placenta by the 16th week.
During the first trimester, the number of glands and blood vessels in this membrane increases.
The middle layer of the uterus is called myometrium and consists of smooth muscle fibers. Under the influence of hormones, these muscles contract and stretch. They are the strongest, because nature is designed to protect the future baby from external shocks and push the child during the birth.
Due to the growth and stretching of these muscles during pregnancy, the uterus increases in size. Muscle cells divide, new muscle fibers are formed; both new and existing ones are 10–12 times longer and 4–5 times thicker.
If before pregnancy, the thickness of the walls of the uterus was 0.5−1 cm, then in the middle of pregnancy – 3-4 cm. After the 30th week, the uterus increases only due to the elongation of muscle fibers and their thinning, and the thickness of its walls decreases to the end of pregnancy previous 0.5-1 cm
And finally, perimetry – the outer layer, or connective tissue. This is the part of the peritoneum that covers the uterus from above, lying loose on it, and holding it in a certain position. During pregnancy, the ligament structure changes.
At the very beginning, they stretch to keep the uterus growing in size, and as it grows they thicken and elongate, which helps to keep the “cradle” in the correct position.
Almost every expectant mother during the ultrasound hears about increasing the tone of the uterus. How dangerous is it?
Muscles, even in a dream, do not relax completely, they maintain a minimum tension – tone. The uterus is a muscular organ, so some tension in its muscles is considered normal. For most of the pregnancy, if there are no complications, the muscles of the uterus are relaxed.
They tense briefly and under certain circumstances. Female hormone progesterone helps them to relax, and beta cells in the muscles of the uterus regulate tone.
Western doctors believe that the increased tone of the uterus at the beginning and in the middle of pregnancy is a physiological process that does not require treatment. Domestic obstetricians and gynecologists hold a different point of view.
The uterus is normal can shrink up to 25 times a day. But with a normal pregnancy, women usually do not feel this. Muscles of the uterus can be strained during an ultrasound, vaginal examination, sexual intercourse or stress.
In this case, possible pain in the lower abdomen. But in such cases, the muscles quickly relax, the pain in two minutes passes.
After 30 weeks, the expectant mother can feel how the uterus contracts when the position of the body changes. But the pain also should not be, because after a minute the uterus relaxes.
Increased uterine tone can cause an abortion, so doctors track it on palpation of the uterus through the abdominal wall, during vaginal examination and ultrasound.
At about 5-6 weeks of pregnancy, an increase in uterus becomes noticeable during a gynecological examination. It is inflated, and the farther, the more “pear” becomes like an “apple”.
By the 8th week, the size of the uterus increases by about 2 times, by the 10th – by 3 times (weight becomes 140 g), by the 12th – by 4 times, and its bottom (upper part) reaches the border of the small pelvis, there is an upper edge of the symphysis joint. From the second trimester, that is, from the 13th to the 14th week, the uterus extends beyond the pelvis, and it can be felt through the anterior abdominal wall.
With a normal pregnancy in the 16th week, the bottom of the uterus is exactly in the middle, between the navel and the pubic joint, located 6 cm above the pubis. The uterus weighs 250 g. At this time, it grows more in length than in width, and, gradually increasing in size, it shifts the internal organs upwards and to the sides.
When a woman is standing, the uterus touches the front wall of the abdomen, when it lies – it is shifted to the spine. With sudden movements, the expectant mother may experience pain in the abdomen and in the back, as the ligaments holding the uterus tighten. In addition, with the growth of the uterus, the center of gravity of the body shifts, the spine experiences additional stress and flexes.
As a result, the woman’s posture changes, which causes discomfort in the lower back. Due to hormonal changes, joint mobility increases.
From the 20th week, the doctor begins to measure the abdominal circumference and the height of the uterus bottom (the distance between the upper edge of the pubic symphysis and the highest point of the uterus, then – the GMR). So he evaluates and tracks the growth rate of the uterus.
Abnormalities are caused by placental insufficiency and such complications of pregnancy as polyhydramnios and multiple births. At this time, the bottom of the uterus is 12 cm above the pubis. Constantly growing uterus puts pressure on the internal organs – the bladder, rectum and stomach.
Because of this, the frequency of urination increases, constipation and heartburn occur.
At the 24th week, the bottom of the uterus is determined at the level of the navel. Due to the increased weight of the uterus, blood flow increases in the pelvic region, the blood vessels around, outside and inside the anus expand and swell.
As a result, hemorrhoids may occur.
At the 28th week, the bottom of the uterus is 24−26 cm above the pubis. Since there is a third circle of blood circulation, which provides blood supply to the future baby, the load on the cardiovascular system increases.
Because of this, shortness of breath appears.
After 30 weeks, the uterus stops growing, but its size increases due to the fact that this organ stretches the baby developing inside and the muscle fibers become thinner.
At the 32nd week, the upper uterus is 28−30 cm above the pubis. Some movements of the child can be quite painful for his mother. Pushing the wall of the uterus, the baby can touch the adjacent organs.
Single palpable uterine contractions are possible – the so-called false, or training, contractions. If they are irregular and short-lived, there is no cause for concern.
At the 36th week, the bottom of the uterus is 34−36 cm above the pubis, or at the level of the end of the sternum. Because of this, it is impossible to breathe deeply.
The uterus displaced all neighboring organs as much as possible (bladder, rectum).
For childbirth, the uterus begins to prepare a few weeks before. Usually after 36 weeks, the woman periodically feels irregular nagging pains in the lower abdomen and in the sacrum area.
This training uterine contractions, the so-called contractions, precursors, are very short.
At 40 weeks, the bottom of the uterus falls slightly: due to the thinning of the muscle fibers, the lower uterine segment stretches and the baby’s head sinks into the pelvis. Dyspnea and heartburn in many expectant mothers disappear, but urination and defecation occur quite often.
At about the same time, due to contractions of the uterus, a mucus plug is released from the cervical canal. This signal means that labor will start very soon.
On the eve of the birth, the uterus weighs already 1 kg, its height is 32 cm, and its width is 20 cm. It can withstand a baby weighing up to 5 kg.
In total, the volume of its cavity at the end of pregnancy increases more than 500 times.
At the moment of birth, the uterus begins to contract first so that the cervix opens and a channel is formed through which the child passes. In the second stage of labor, contractions, which are already called attempts, are needed to expel the baby.
And, finally, in the early postpartum period, thanks to them the afterbirth is separated.
But this is not the end. The uterus must return to its previous size.
After birth, oxytocin continues to be actively produced. Due to this, in the first week after birth, the weight of the uterus is reduced by half. By the end of the 2nd week it already weighs 350 g, by the end of the 3rd – 250.
By the end of the 6−8th – 70-75 g. On the first day after birth, the bottom is usually at the level of the navel. Over the next approximately 2 weeks, it will drop by about 1 cm daily.
WDM is 11 cm on the 4th day, 9 cm on the 6th, 7 cm on the 8th, and 6 cm on the 10th. By the end of the 10–14th day, the uterus is hidden behind the bosom.
Finally, the form will be restored to 8−9th week after delivery.
While the woman is in the maternity hospital, doctors are tracking the uterine contractions. To ensure that the process is proceeding properly, you should definitely see your doctor about 6–7 weeks after discharge.