The cervix during pregnancy: length norms by week in the table and reasons for deviations

The cervix is essential to preserving a healthy environment for the growing fetus during pregnancy. Most expectant mothers don’t give it much thought until they hear someone bring it up during a checkup or ultrasound, but being aware of its significance can ease anxiety.

As the pregnancy goes on, the length of the cervix can change, and medical professionals frequently keep a close eye on it to make sure everything is going as planned. A cervix that is excessively long or short may indicate specific risks, so it’s important to understand what’s normal for each stage of pregnancy.

This article will discuss the normal cervical length by week, the meaning of those measurements, and the reasons behind occasional deviations. Expectant mothers can feel more informed and at ease throughout their pregnancy journey by being aware of these changes.

What is it

The Latin term for the lower portion of a woman’s primary reproductive organ is cervix uteri. The lower portion of the cervix enters the vagina, the upper part of the cervix communicates with the uterine cavity, and the cervical canal passes inside the cervix.

This cylinder-shaped portion of the uterus has been given significant roles by nature.

The cervix serves as a "gatekeeper" before conception, securely shutting off the entrance for germs, infection, and potentially sperm if they arrive at the wrong time. The cervical canal is entirely sealed off by the mucus.

Every month the neck is satisfied with the "Open Day"; this occurs prior to ovulation, when под воздействием гормонов слизь становится жидкой, освобождая проход в цервикальный канал для мужских половых клеток. If a pregnancy has developed, the cervix once more "seals" the mucous membrane’s passage, ensuring that the growing embryo and, eventually, the fetus, are safe from pathogens, fungi, harmful microflora, and other hazards. Furthermore, the baby’s neck must remain in the uterus until childbirth occurs. Pregnancy termination is a real possibility if it is weak and unable to handle this task.

A small cervix can open up to such an extent during childbirth that the baby’s head can fit through it, which is very significant. After nine months, the baby exits the mother’s womb through the cervical canal to start a life on its own. In terms of anatomy, the cervix is quite intricate. During a standard examination with a mirror, doctors examine its vaginal part. The vaginal vaults, which are deeper structures, are what allow the cervix to join the uterine cavity. One gynecological mirror will not be sufficient to examine them; instead, a colposcope is required, and the examination process is known as colposcopy.

How and why the measurement takes place

Two methods are used to measure the parameters of the cervix: using ultrasound diagnostics and a mirror and colposcope on a gynecological chair. A manual examination allows the physician to assess the cervical canal’s closure or opening, the density of the cervix, and the state of the external os.

A more precise assessment of the condition of the internal os, or the junction with the uterine cavity, which cannot be evaluated in any other way, can be obtained via ultrasound in addition to measuring the length. The physician performs a manual examination during registration and collects vaginal flora smears for analysis. The woman also gets a colposcopy in the first trimester, which provides more details than a standard speculum examination.

It is best to measure the length of the cervix only after the 16th week of pregnancy, when the baby starts to grow actively and the cervix is under more pressure.

Up to 16 weeks, the length of the cervix varies among pregnant women, much here depends on individual values. However, by the 16th week, the sizes of the lower part of the uterus in different women come to uniform average values, and the length becomes diagnostically important. In the middle of pregnancy, ultrasound is usually done transabdominally, placing the scanner sensor on the pregnant woman"s abdomen, conducting an examination through the anterior abdominal wall. If there is a suspicion of lengthening or shortening of the cervix, as well as other anomalies, the doctor uses an intravaginal ultrasound method, in which the sensor is inserted into the vagina. Through the thinner vaginal wall, the cervix is ​​visible as well as possible.

In order to prevent intrauterine infection, which can also occur if the cervical canal opens slightly or completely, and to make sure the child is not at risk of an early birth, it is important to keep an eye on the size and other characteristics of the cervix. A healthy woman has her cervix examined four times during the course of having a child. As many times as needed, and more frequently, diagnostics will be recommended if there is reason for concern.

Changes during pregnancy

The cervix of a non-pregnant woman measures about 3–4 cm in length and 2.5 cm in width. These are not hard and fast numbers; there might be some individual variances. When a woman is planning a pregnancy but is not pregnant, her cervix is smooth, pink, and has a slightly shiny appearance when viewed under a speculum.

In the early stages

The cervix experiences significant internal and external changes during pregnancy. The delicate pink color is replaced by a purple, bluish, cyanotic hue as a result of the increased blood supply. The nine-month-long process of "maturation" starts because the small cervix needs to grow, thicken, and become more elastic in order to guarantee the baby’s passage during labor. Doctors can assess the cervix’s condition in the first trimester to determine whether a spontaneous pregnancy termination or miscarriage is possible. Such unfavorable events are highly likely if the cervix is loose and permits the gynecologist’s finger to pass through it during examination.

The cervix should normally be tightly closed and veer slightly towards the anus in the early stages.

In addition to increasing the risk of miscarriage, a cervical canal that is not tightly closed increases the risk of pathogenic bacteria, fungi, and viruses entering the uterus, which can harm the fetal membranes and cause the fetus to die. Intrauterine infections can occasionally result in congenital illnesses, such as birth defects and malformations. The initial alterations in the neck occur around week 4 of pregnancy, at which point the яйцо растущее плодное начинает несколько выпячивать стенку матки, к которой оно прикрепилось. This leads to a minor asymmetry.

The neck changes its position in space, if during ovulation it rose higher to increase the chances of the penetration of sperm, now the main task is to not miss the fetal egg, for this the lower segment of the uterus has to go down and deviate back. Many women who want to quickly find out whether pregnancy has come, interests what the neck should be to the touch, because it is no secret that many planning pregnancy are carried out at home on their own. Approximately 8-10 days after conception, under the influence of the hormone progesterone, the cervix becomes softer. The cervical canal, on the contrary, closes more tightly. A hard cervix in the early stages may indicate a threat associated with increased tone of the uterus itself. This can happen, for example, with autoimmune diseases or with a lack of progesterone.

In the later stages

During the third trimester, medical professionals determine when the baby will arrive based on the state of the cervix. The uterine wall softens in this area. The cervix progressively gets shorter by about half, and an ultrasound shows how the internal os expands in preparation for the impending birth. This is a gradual process that takes several months to complete. Estrogens are one of the hormones that cause changes. The doctor can start assessing the cervix’s preparedness for childbirth at 38 or 39 weeks. The cervical canal’s capacity to accommodate the examining physician’s finger passing through it can be used to assess this preparedness.

Such a palpation cannot be performed on oneself and, fortunately, is technically quite challenging.

Sometimes, a week or a few days before the birth, a woman may notice the discharge of the mucus plug, the very one that served as an obstacle to pathogenic microbes throughout the pregnancy. The cervix gradually smooths out and begins to expand. In some women, such preparation of the cervix “starts” only at 40 weeks, and in some – even later. If a woman gives birth to her first child, it is possible that the cervix may begin to change in advance, and it will do so rather slowly. In women giving birth again, preparation begins later and proceeds more quickly. In them, the cervix “remembers” how to behave in the current circumstances.

Doctors can recommend prophylactic treatment to help the cervix "ripen" more quickly if it is not in a rush. Modern gynecologists disagree about the wisdom of such stimulation. While some medical professionals are certain that stimulation is essential, others think you should wait and put your trust in nature, as it is the source of wisdom when it comes time for a child to be born.

Length norms by week

The likelihood of saving a problematic pregnancy is nearly 95% if you identify deviations in the cervix’s condition in a timely manner. This is because modern medicine has several tools at its disposal to modify the cervix’s behavior, including medications, obstetric pessaries, special fixators that are placed directly on the cervix, and minor surgical procedures like suturing. Because of this, it’s critical to check expectant mothers at least four times throughout the course of the pregnancy.

Scheduled exams are performed at 20 and 28 weeks, provided there is no cause for concern regarding the mother’s or child’s health. then at weeks 32 and 36. The examination and measurement of the cervix’s length will be performed on an emergency basis if the doctor is concerned and the patient complains of pain or discharge that cannot be regarded as typical for pregnancy.

This table will teach you about the typical cervix length for various stages of pregnancy and how this indicator varies week by week. Cervical length:

Obstetric period	Average length, mm	First pregnancy	Repeated pregnancy	Normal range, mm	Possible deviation, mm
10-14 weeks	35.4	35.3	35.6	28-45	5.1
15-19 weeks	36.2	36.5	36.7	30-48	5.3
20-24 weeks	40.3	40.4	40.1	32-48	4.5
25-29 weeks	41	40.9	42.3	34-49	4.3
30-34 weeks	36.4	35.8	36.3	34-43	3.7
35-40 weeks and more	28.6	28.1	28.4	20-37	4.5

The length of the cervix at the start of pregnancy increases more slowly in women who are about to give birth than in women who have already given birth, as the table illustrates. Using a unique scale designed for this purpose, the normal size of the cervix is measured in the third trimester.

A clinical picture that is roughly accurate is produced by evaluating each indicator at a predetermined number of points.

• Consistency. Dense – 0 points, slightly softened – 1 point, soft – 2 points.
• Length. More than 20 mm — 0 points, 10-20 mm — 1 point, less than 10 mm — 2 points.
• Position in space. The cervix is ​​tilted back — 0 points, tilted forward — 1 point, is located directly in the center perpendicular to the entrance to the vagina — 2 points.
• Degree of opening. If the doctor"s finger does not pass into the cervical canal — 0 points, if 1 finger passes — 1 point, if 2 or more fingers pass — 2 points.

Throughout pregnancy, the cervix is an important organ, and its length is a major sign of how the pregnancy is doing. The cervix should remain a specific length during the weeks to support the developing baby and aid in delaying premature labor. Expectant mothers and their doctors can monitor changes with the aid of a weekly norms table; any deviations from these norms could indicate possible problems, like an increased risk of preterm birth. Knowing why these changes are occurring can help guarantee appropriate treatment and prompt interventions to support a healthy pregnancy.

Possible deviations and their causes

Women in the "position" often have many questions when measurements and comparisons of results with current norms are made. In fact, deviations may be signs of trouble. Let’s examine the most typical anomalies and the reasons behind them.

Pregnancy in the cervix

The doctor may suspect a "cervical pregnancy" if the cervix enlarges more than usual in the early stages. This kind of ectopic pregnancy occurs when the fertilized egg is implanted in the cervix or isthmus rather than the uterine cavity, as would naturally occur.

The embryo can potentially survive and develop there for four to five weeks, or, less frequently, for seven to seven weeks. From this point on, the situation gets intolerable, the fetus dies and is rejected, and a miscarriage happens, sometimes with a significant blood loss.

The pathology is diagnosed in less than 0.01% of pregnancies and is thought to be extremely rare. There are several reasons why the fertilized egg may adhere to the cervical canal walls; many of these are still poorly understood in modern medicine.

According to medical opinion, this happens when the uterine conditions are not met for implantation; in such a case, the blastocyst finds its way into the cervix in search of a place to stay.

The woman may have disregarded the advice to use protection for a specific amount of time following a recent abortion as the cause. If less than two to three years have passed since the cesarean section, a young mother’s decision to become pregnant can turn into a cervical pregnancy.

Additionally, women who have had uterine fibroids and adhesions diagnosed in the past are more vulnerable than others.

Any type of intervention, including surgery, wounds, and uterine inflammation, may result in a cervical or isthmic pregnancy later on. It’s possible that no symptoms exist. During the examination, the doctor will first notice that the patient has an excessively large cervix and a small uterine cavity. An ultrasound is then advised as a next step.

A blood test to measure the hormone known as chorionic gonadotropin, which is present in all pregnant women from the day of implantation, reveals an abnormally low level of hCG for the day the last menstrual period was reported.

A fertilized egg will be discovered in the cervical canal after a thorough examination by the doctor, who will not detect it in the uterus during an ultrasound. A few decades ago, the uterus had to be removed entirely in order to address this issue. Many women who became pregnant through cervical cancer were unable to become pregnant again.

These days, vacuum aspiration and laser excision of the area where the embryo grows into the cervix are less traumatic ways to assist a woman and protect her chances of becoming a mother in the future. Although there is a significant chance of complications following such interventions, modern medicine manages the task fairly well.

Short cervix

Less than 25–27 mm at the start of pregnancy, a short cervix can result from both congenital abnormalities in a woman’s reproductive organ structure and traumatic events, such as abortions or inflammatory processes that shorten the lower segment of the uterus. In any event, the woman and the child are seriously at risk due to the short length of this reproductive system.

The cervix typically lengthens at the start of pregnancy and shortens as delivery approaches. At first, a short cervix will find it extremely difficult to support a developing baby inside the uterus. There could be a miscarriage, an early birth, an abrupt labor, or a cervical rupture.

Because a shorter cervix is less able to protect the fetus from viruses and other pathogenic microbes, there is a higher chance of intrauterine infection.

If the shortening occurred prior to the start of the pregnancy, the doctor will be able to identify it during the initial consultation. But because of the subsequent development of a short cervix, for example, and the hormonal insufficiency that existed during the first trimester, the issue is not identified until the expectant mother visits for a screening examination at 12 weeks of pregnancy.

After this time, closer to the fourth month of pregnancy, symptoms may occasionally start to show.

The woman may start to complain of lower abdominal pain and occasionally light bleeding as the growing baby starts to put more noticeable pressure on the short cervix.

In this instance, the discharge is usually serous or bloody, occasionally accompanied by mucus. The question of how to assist gets answered if vaginal ultrasonography results confirm shortening. Sometimes drugs, such as hormones, can make the neck stronger if there are insufficient amounts of them, but the neck cannot lengthen under any circumstances.

Such a future mother will be monitored more closely during her pregnancy and may need to be hospitalized in order to receive treatment intended to preserve and extend her pregnancy.

A pessary, a unique ring that fixes the cervix and lessens the strain of a developing detrusive organ on a short neck, can be used to install it.

There is also a Serklyazh method. Its foundation is the application of seams to the neck, which will mechanically stop it from disclosing too soon. It makes sense to suture only during the first 24 to 25 weeks of pregnancy; beyond this time, people try to avoid doing cerclage.

Long cervix

A long cervix may develop from birth or may become so as a result of surgical procedures such as curettage and abortions, as well as inflammatory disorders affecting the uterus, appendages, and ovaries. Frequently, the onset of this type of pathology coincides with pregnancy.

Because of the abnormal proportions of the reproductive organ caused by the elongation of the lower segment of the uterus, there is a higher chance of a pathological placental attachment when this temporary organ is positioned in the middle, too low, or to the side.

Particularly in the second and third trimesters, the placenta’s height is crucial because it determines how well the unborn child will receive all the nutrients and oxygen it needs.

During childbirth, women who have a pathologically elongated cervix are at risk. The act of giving birth itself is a lengthy one; the birth of the firstborns lasted nearly 14 hours, and the birth of multiples lasted 9–12 hours.

The longer, slower, and more painful opening of the elongated organ.

Since the head and neck are in the same plane, a child’s risk of hypoxia increases when they pass through such a canal.

What makes things difficult is that a gynecologist’s routine examination cannot identify the pathology. Only a colposcopy can detect an anomaly, and only ultrasound diagnostics can confirm or disprove it.

Since a long cervix can smooth out and decrease with childbirth, such a deviation does not require special treatment. In the event that this does not occur, physicians will most likely employ a labor-inducing technique.

It is recommended that a woman receive massage therapy prior to childbirth in order to facilitate the outflow of lymph and strengthen the muscles surrounding the pelvic organs. Rarely are medications prescribed; when they are, it’s usually for post-term pregnancies in hospitals.

Cervical ectopia (erosion)

A portion of the columnar epithelium migrates into the vagina with this pathology. The physician notices a red area that appears to be erosive changes while doing an examination.

A woman may report having a lot of discharge that smells bad and is yellow, white, or greenish in color. These complaints suggest that infections are either present or have occurred in the past.

Ectopia risk factors include past abortions, hormone imbalances, and childbirth. Doctors are generally optimistic about ectopia, though, as it also has physiological causes.

Pregnancy-related alterations to the lower segment of the uterus result in modifications to the organ’s tissues. Cervical ectopia following childbirth necessitates monitoring, including annual colposcopy, oncocytology, and control of HPV carriage.

The doctor can report that the length is normal, but there is ectopia of the cervix ("erosion") based on the results of this organ’s biometrics and manual examination. Over 60% of expectant mothers experience this phenomenon. Before becoming pregnant, some women experienced changes in the cervix mucous membrane; however, "erosion" may occur during pregnancy.

There are several explanations. A long-term human papillomavirus (HPV) infection combined with prior inflammations can alter the mucous membrane, although "erosion" may not always become apparent until after pregnancy.

Women who have experienced repeated abortions, difficult childbirth that injured this organ, or sexually transmitted infections are more susceptible to "Erosion."

The symptoms are palpable for a woman. Changes in the cervix’s mucous membrane can cause discomfort "inside" during sexual activity at any point in pregnancy. Expectant mothers have also occasionally complained of the appearance of bloody or scanty pink discharge. Over 50% of women experience no symptoms at all.

"Erosion" is not treated during pregnancy unless it is accompanied by significant precancerous changes.

Cauterization and laser exposure are two unpleasant methods of treating this issue that are not recommended for expectant mothers due to the risk of scarring, which can lead to a lot of issues and pain during childbirth and increase the risk of organ rupture. Treatment is therefore put off until later. Should an examination reveal cancerous alterations on the cervix, the question of whether the pregnancy can be prolonged may come up. Naturally, a council of physicians and the expectant mother decide on this matter.

The course of pregnancy and the fetus are unaffected by a typical ectopia of the cervix.

Dysplasia

Cervical dysplasia is another issue that a colposcopy may reveal. This term describes epithelium alterations that have precancerous precursors. The disease is most frequently found in women between the ages of 25 and 33–35. Positive outcomes can be prevented and dysplasia is thought to be fully reversible if the condition is detected early.

Because of their similar clinical presentations, dysplasia and "erosion" can be mistaken for one another during a manual examination. However, colposcopy and laboratory tests help distinguish between the two conditions. The reason for this is that while cervical ectopia ("erosion") causes superficial, mechanical epithelium damage, dysplasia causes cellular damage, which results in deeper, more profound epithelium destruction.

The disease is most frequently brought on by human papillomavirus types 16 and 18. Other factors that actively "help" the disease progress include smoking, immunodeficiency or weakened immunity, and long-term untreated chronic inflammatory processes in the reproductive organs.

Hormonal changes brought on by natural causes may have an impact on the development of dysplasia during pregnancy. Early birth and excessively early sexual activity are additional risk factors.

Contemporary therapeutic approaches, including medication and surgery, along with ongoing monitoring of the organ’s condition, all contribute to the prevention of cancer. However, using drugs and particularly surgery during pregnancy is not recommended. Since mild dysplasia rarely progresses to cancer, observation is all that is necessary.

A severe case of the illness may force a woman to decide between having an abortion and consenting to an immediate operation, or to keep the child.

The matter is resolved on an individual basis in each unique situation.

Medical statistics are not very promising: approximately 30% of expectant mothers who decided to become pregnant and delay gynecological surgery later registered at an oncology center because they had developed cervical cancer.

Week of Pregnancy	Cervix Length (cm)	Reasons for Deviations
12-14 weeks	3.5-4.5 cm	Shorter length may indicate risk of preterm birth
20 weeks	3.5-4.0 cm	If cervix shortens early, medical monitoring is needed
24 weeks	3.0-3.5 cm	Short cervix might require a cerclage or bed rest
28 weeks	2.5-3.0 cm	Shortened cervix increases risk of premature labor
32 weeks	2.5-3.0 cm	Close monitoring may be needed to prevent complications
36 weeks	2.0-2.5 cm	Short cervix at this stage may not be a concern as labor approaches

In order to support the developing baby and ensure a smooth pregnancy, the length of the cervix is important during pregnancy. Keeping an eye on it enables you to avert possible issues and take appropriate action when needed.

Expectant moms can feel more knowledgeable and confident if they know what the weekly norms are. While departures from these norms don’t always indicate that you should panic, they do call for notice and, in certain situations, medical assistance.

Most cervical length-related problems are manageable with knowledge and frequent consultation with healthcare professionals, protecting mother and child’s health and safety.

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