Pelvic dimensions in obstetrics: table, normal, wide, narrow clinical, narrow anatomical

Basic parameters of the large pelvis

The female pelvis differs significantly in size from the male one. It is important for a girl to know several parameters and their meanings to make sure that doctors are acting correctly:

1. The spinarum distance is normally 25-26 cm - this is the distance between the anterosuperior spines of the bones of the iliac zone.
2. The cristarum distance – normally 28-29 cm – is the position of the distant promontories of the iliac crests, located above the attachment of the hip joint.
3. External conjugate - from 20 to 21 cm - the distance from the middle of the top of the symphysis to the upper corner of the Michaelis rhombus.

An awn is an acute formation on the bones, which is diagnosed both normally and in various diseases. Osteophytes and osteoporosis are derivatives of this word.

Narrowing of the female pelvis is a common problem in obstetrics. This indicator matters:

• at grade 1 - the mildest - the true conjugate retains a size greater than 9, but less than 11 cm;
• with degree 2 narrowing of the pelvis, this figure is 7 and 9 cm, respectively;
• at grade 3 – 5 and 7 cm;
• at grade 4, the true conjugate barely reaches 5 cm.

The true conjugate of the pelvis is the distance from the protruding part of the sacrum to the superior promontory of the pubic symphysis at the exit. The easiest way to determine the parameter is by the dimensions of the conjugates on the outside.

A true conjugate is the smallest distance inside through which the fetus emerges during childbirth. If the indicator is less than 10.5 cm, then doctors prohibit natural childbirth. The true conjugate parameter is established by subtracting 9 cm from the external indicator.

The diagonal conjugate is the distance from the bottom of the symphysis pubis to the prominent point of the sacrum. It is determined using vaginal diagnostics. With a normal pelvis, the figure does not exceed 13 cm, sometimes it is at least 12 cm. To clarify the true conjugate, 1.5-2 cm is subtracted from the resulting figure.

When examining the diagonal indicator, the doctor in rare cases reaches the promontory of the sacrum with his fingers. Usually, if the bone is not felt when you place your fingers inside the vagina, the size of the pelvis is considered normal.

The shape of the pelvis can affect normal indicators. With a platipeloid constitution, which occurs in 3% of women, the pelvis is elongated and slightly flattened. In this case, the gap between the bones narrows, as a result of which the birth process can be complicated.

Normal anatomy of the pelvic organs and mechanisms of fertilization

All women know about the presence of internal genital organs: the uterus and appendages. However, few people can imagine what the internal genital organs actually look like.

To the internal genitals

organs include the ovaries, fallopian tubes, uterus and vagina.

To the external genitalia

include the pubis, labia minora, labia majora and clitoris. All genital organs reach full development with the onset of puberty, when their cyclic activity is established, controlled by hormonal and nervous mechanisms.

Ovary, fallopian tube and uterus

1 - fundus of the uterus; 2 - isthmus of the fallopian tube; 3 - own ligament of the ovary; 4 - mesentery of the ovary; 5 - ampulla of the fallopian tube; 6 - fimbriae of the fallopian tube; 7 - abdominal opening of the fallopian tube; 8 - body of the uterus; 9 - ovary; 10 - suspensory ligament of the ovary; 11 - cervix; 12 - round uterine ligament; 13 - wide uterine ligament; 14 - vagina

Ovary

performs 2 main functions in a woman’s body: firstly,
generative,
that is, sex cells (eggs) are formed in it, which are involved in reproduction, and
endocrine
, that is, sex hormones are produced in it, both male and female.
The ovary consists of follicles. Once a month, normally, one of the follicles, under the influence of certain hormones, begins to mature, reaches its maximum size (about 20 mm) by the middle of the menstrual cycle, and on average, on the 14-15th day of a 30-day menstrual cycle, the so-called dominant follicle ruptures with release from it an egg is released, which then enters the fallopian tube. The release of an egg from a dominant follicle is called “ovulation
.
In place of the ruptured follicle, the walls of which collapse, a blood clot forms, which is then replaced by connective tissue and “resolves.” This formation in the ovary at the site of a ruptured follicle is called the “corpus luteum
. Indirectly, by its presence during an ultrasound examination performed in the second phase of the ovarian-menstrual cycle, one can judge the presence or absence of ovulation.

Mechanisms of ovulation:

The reasons for the selection and development of a dominant follicle from a huge number of primordial follicles have not yet been clarified. During the first phase of the cycle, there is a 100-fold increase in the volume of follicular fluid, in which the content of estradiol and FSH (follicle-stimulating hormone) also sharply increases. An increase in estradiol levels stimulates the release of LH (luteotropic hormone).

The process of ovulation itself is a rupture of the membrane of the dominant follicle and bleeding from the destroyed capillaries. Sometimes this process is accompanied by discomfort in the lower abdomen or pain (for example, pain during ovulation is one of the characteristic signs of endometriosis). Changes in the follicle wall that cause its thinning or rupture are determined by special enzymes (collagenase). After the release of the egg, the forming capillaries begin to grow into the cavity of the follicle, the place begins to be replaced by adipose tissue (i.e., the cells that were in the follicle (granulosa cells) are replaced by fatty ones).

A full-fledged corpus luteum is formed only when the dominant follicle has the required number of granulosa cells with a high content of LH receptors

.

The increase in the size of the corpus luteum after ovulation occurs mainly due to an increase in the size of granulosa cells. The human corpus luteum produces progesterone, estradiol and androgens, i.e. male sex hormones.

A woman's menstrual cycle is conventionally divided into 2 phases. The first day of the cycle is considered the first day of menstruation.

The 1st phase lasts from the first day of the menstrual cycle until ovulation, on average, its duration is 10-14 days. The 2nd phase begins after ovulation and lasts until the onset of menstruation. During this period, the woman’s body prepares for a possible pregnancy.

Uterus

is a hollow organ with a thick muscular wall in which fetal development occurs.
The wall of the uterine body
consists of 3 layers: 1.
Endometrium
- the mucous membrane of the uterine cavity, which undergoes changes during one menstrual cycle.
Each cycle ends with the removal of part of the endometrium, which is accompanied by the release of blood (menstruation); 2. Myometrium
is the thickest muscular layer of the uterine wall;
3. Perimetry
- the serous membrane of the uterus.

Oviduct

- a tubular organ that performs a number of functions:

1. Captures the egg released from the ovary during ovulation; 2. Carries out its transfer in the direction of the uterus; 3. Creates conditions for the transport of sperm in the direction from the uterus; 4. Provides the environment necessary for fertilization and initial development of the embryo; 5. Transports the embryo to the uterus; 6. In the fallopian tube, the egg can “meet” the sperm, and in this case fertilization occurs. The fertilized egg moves through the tube into the uterine cavity within 4-5 days, where it then attaches to the already prepared thickened endometrium (mucous lining of the uterine cavity). If the patency of the fallopian tubes is impaired, with adhesions in the pelvis or endometriosis, the fertilized egg may not complete its transport into the uterine cavity and attach to various parts of the fallopian tube. In this case, a pathology called ectopic pregnancy occurs.

Pelvic planes

To understand the exact characteristics of the female skeleton, it is necessary to measure the plane before giving birth:

1. Entrance plane . In front, it starts from the top of the symphysis and reaches behind the promontory, and the lateral distance is bordered by the innominate line. The direct size of the entrance corresponds to the true conjugate - 11 cm. The transverse size of 1 plane is between distant points of the boundary lines, not less than 13 cm. The oblique sizes start from the sacroiliac joint and continue to the pubic tubercle - from 12 to 12.5 cm normally. The entrance plane usually has a transverse oval shape.
2. The plane of the wide part . It runs through the inner surface of the pubis strictly in the middle, passes along the sacrum and the projection of the acetabulum. It has a round shape. The straight size is measured, which is normally 12.5 cm. It starts from the middle of the pubic symphysis and extends to the 2nd and 3rd vertebrae of the sacrum above the buttocks. The transverse size of the zone is 12.5 cm, measured from the middle of one plate to the other.
3. The plane of the narrow part . It starts from the bottom of the symphysis and reaches behind the sacrococcygeal joint. On the sides the plane is limited by the ischial spines. The straight size is 11 cm, the transverse size is 10 cm.
4. Exit plane . It connects the lower edge of the symphysis with the edge of the coccyx at an angle, along the edges it goes into the ischia bones located in the buttocks area. The direct size is 9.5 cm (if the tailbone is deviated, then 11.5 cm), and the transverse size is 10.5 cm.

In order not to get confused in all the indicators, you can only pay attention to the measurement of the large pelvis. The table shows an additional parameter - the distance between the trochanters of the femurs.

The trochanters of the femurs are located at the point where girls usually measure the volume of their hips.

obstetrics and gynecology

4. Anatomy of the female pelvis

The structure of a woman’s bony pelvis is very important in obstetrics, since the pelvis serves as the birth canal through which the emerging fetus moves. The pelvis consists of four bones: two pelvic bones, the sacrum and the coccyx.

Pelvic (nameless) bone

consists of three bones fused together: the ilium, pubis and ischium. The ilium consists of a body and a wing, extended upward and ending in a crest. In front, the crest has two projections - the anterosuperior and anterioinferior spines; in the back there are posterosuperior and posteroinferior spines. The ischium consists of a body and two branches. The superior branch runs from the body downwards and ends at the ischial tuberosity. The lower branch is directed anteriorly and upward. On its posterior surface there is a protrusion - the ischial spine. The pubic bone has a body, superior and inferior branches. On the upper edge of the superior ramus of the pubic bone there is a sharp ridge, which ends in front with the pubic tubercle.

Sacrum

consists of five fused vertebrae. On the anterior surface of the base of the sacrum there is a protrusion - the sacral promontory (promontorium). The apex of the sacrum is movably connected to the coccyx, which consists of four to five undeveloped fused vertebrae. There are two sections of the pelvis: the large and small pelvis, between them there is a border or innominate line. The large pelvis is accessible for external examination and measurement, unlike the small pelvis. In the small pelvis there are an entrance, a cavity and an exit. The pelvic cavity has a narrow and a wide part. Accordingly, four planes of the small pelvis are conventionally distinguished. The plane of entrance to the small pelvis is the boundary between the large and small pelvis. At the entrance to the pelvis, the largest dimension is the transverse one.

In the pelvic cavity, the plane of the wide part of the pelvic cavity, in which the straight and transverse dimensions are equal, is conventionally distinguished, and the plane of the narrow part of the pelvic cavity, where the straight dimensions are slightly larger than the transverse ones. In the plane of the outlet of the small pelvis and the plane of the narrow part of the small pelvis, the direct dimension prevails over the transverse one. In obstetrics, the following dimensions of the small pelvis are important: true conjugate, diagonal conjugate and direct size of the pelvic outlet. The true, or obstetric, conjugate is 11 cm.

The diagonal conjugate is determined during vaginal examination; it is 12.5–13 cm. The direct size of the pelvic outlet is 9.5 cm. During childbirth, as the fetus passes through the pelvis, this size increases by 1.5–2 cm due to the deviation of the apex coccyx posteriorly. The soft tissues of the pelvis cover the bony pelvis from the outer and inner surfaces and are represented by ligaments that strengthen the joints of the pelvis, as well as muscles. The muscles located at the pelvic outlet are important in obstetrics. They cover the bony canal of the small pelvis from below and form the pelvic floor.

Obstetric (anterior) perineum

called that part of the pelvic floor that is located between the anus and the posterior commissure of the labia. The part of the pelvic floor between the anus and the tailbone is called the posterior perineum.

Determining the size of the pelvis: narrow or wide

By comparing the obtained indicators, it is easy to determine whether a woman has wide or narrow hips. After consulting with a gynecologist and determining whether the size of the female pelvis is normal, you can decide whether to have a caesarean section or give birth on your own.

Indicators are higher than normal

In most cases, a wide female pelvis is a good factor for pregnancy. Girls should understand that if a woman loses weight, the pelvis cannot become narrower because of this - everything is inherent in the structure of the bones. Wide hips are most often found in large women, and this cannot be considered a pathology. If the dimensions exceed the norm by 2-3 centimeters, this is considered a wide pelvis.

The main danger of too wide hips is rapid labor. In such a situation, the child passes much faster through the birth canal, which can lead to female injuries: rupture of the cervix, vagina and perineum.

Anatomically narrow pelvis

The definition of an anatomically narrow pelvis in obstetrics is closely related to normal indicators. A deviation of 1.5 cm from the minimum limit indicates that the woman has small hips. In this case, the conjugate should be less than 11 cm. Natural birth in this case is possible only when the child is small.

When diagnosing, the doctor identifies the type of pelvis: transversely narrowed, uniformly narrowed, flat, simple or rachitic. Less common are pathological forms in which the pelvis has begun to be narrowed by pathological changes in the bone structure: kyphotic, deformed, obliquely displaced or spondylolisthetic pelvis. Causes of anatomically narrow pelvis:

• bone injuries;
• rickets;
• increased physical activity and lack of proper nutrition in childhood;
• neoplasms in the study area;
• hyperandrogenism, leading to male type formation;
• accelerated growth during adolescence;
• psycho-emotional stress that caused compensatory development in childhood;
• general physiological or sexual infantilism;
• Cerebral palsy, birth injuries, polio;
• professional sports;
• metabolic problems;
• dislocations of the hip joints;
• inflammatory or infectious diseases of the skeletal system;
• rachiocampsis.

Factors such as hormonal imbalance, constant colds and problems with the menstrual cycle provoke improper formation of the pelvis.

Clinically narrow pelvis

Clinically, a narrow pelvis can be identified only before childbirth, or during the process of delivery. This is due to the discrepancy between the size of the fetus and the woman’s birth canal. For example, if the child’s weight is more than 4 kg, even a girl with normal indicators can be diagnosed with a “clinically narrow pelvis”. There is no single answer to the question of why this condition is formed. The doctor identifies a whole range of reasons:

• large fruit;
• post-term for more than 40 weeks;
• malposition;
• tumors of the uterus or ovaries;
• fetal hydrocephalus (enlarged head);
• fusion of the vaginal walls;
• breech presentation of the fetus (the baby is turned with the pelvis instead of the head).

In obstetric practice, there are more and more cases of clinically narrow birth canal, because large children are born.

Every woman should know her pelvic parameters before giving birth. A responsible gynecologist never ignores these indicators and carefully conducts the examination using an obstetric caliper.

Scientists have explained how the shape of the female pelvis changes throughout life

No matter how much scientists struggle to study nature, constantly improving their methods, it still remains the biggest mystery. Researchers still never cease to be amazed at how well thought out and organized everything is in the living world.

Jealousy is a reason for a medical examination

A 43-year-old resident of Turkey unreasonably began to be jealous of her faithful husband, with whom she had been married for 20...

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Anthropologists and biologists from Switzerland and Belgium, in the course of joint research, found evidence that the shape and size of the pelvis in women can change, adapting to the appearance of offspring. The progress of the research and analysis of the data obtained have been published

in the latest edition of the Proceedings of the National Academy of Sciences.

The structure of the human pelvis is classified as sexual dimorphism, that is, it distinguishes males and females from each other. Typically, women's hips are wider and more rounded than men's.

Studying the structure of the female skeleton, scientists put forward the hypothesis of the so-called obstetric dilemma. On the one hand, the female pelvis must be relatively wide in order to facilitate the birth of babies, who, if positioned correctly in the womb, go head first. On the other hand, a narrow pelvis makes it easier for a person to walk upright. Recently, this hypothesis has been challenged on the basis of biomechanical and biocultural indicators, as well as metabolic processes. However, until the latest research by Swiss and Belgian scientists, it remained unclear exactly what factors are responsible for differences in the shape and size of the pelvis in adult men and women.

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When starting scientific work, the researchers put forward the following assumption: throughout life, the structure of the pelvis in women specifically changes, making it easier to give birth to children. To test their own hypothesis, a group of scientists invited 275 women of different ages up to 95 years to participate in the study. The authors of the work used computed tomography methods and also studied geometric morphometry, that is, they analyzed the relationship between the sizes and shapes of parts of the pelvis. The data obtained were compared with existing information on the structure of the pelvis in men.

The results obtained showed that before the onset of puberty, the structure of the pelvis in boys and girls shows virtually no differences, and all changes occur in the same way.

With the onset of active sexual development, which in some girls occurs already at the age of 10 years, the shape and size of the female pelvis changes according to its own unique laws.

The processes that prepare the female body for the birth of children are completed at approximately 25 years of age. Scientists note that the period when differences in the structure of the pelvis in women and men are most noticeable coincides with the peak of fertility. According to researchers, in women this age occurs on average from 25 to 30 years. Biologists have noticed a curious feature: at the age of 40 to 45 years, the structure of the female pelvis continues to develop, but the changes again proceed in a similar way to the male pelvis. Transformations lead to a reduction in the size of the birth canal (the birth canal is a canal formed by the bones of the small pelvis and the soft tissues located in it, through which the fetus and placenta pass during childbirth).

Swiss and Belgian scientists suggest that all changes in the shape and size of the female pelvis, depending on age, may be associated with the production of hormones during puberty and before the onset of menopause. According to biologists, estradiol, which is part of the group of female sex hormones - estrogens, takes the most active part. It depends on him how round the outlines of the female figure will be. Estradiol is often called the “pregnancy hormone”, as it regulates blood circulation in the pelvic cavity, controls the increase in the size of the uterus, and is also responsible for the formation of the placenta.