Pelvic measurement is mandatory for all pregnant women. This is a quick, painless and absolutely harmless procedure, the implementation of which is an indispensable condition for obtaining a pregnant woman’s card when a woman first contacts a gynecologist. Based on this, you can plan the management of childbirth: naturally or surgically (caesarean section). Timely choice of tactics allows you to avoid many complications that pose a threat to the life of a woman and her baby. A properly planned birth is a guarantee that the birth of a child will be easy and safe.
The true conjugate is the shortest promontory and the most protruding point into the pelvic cavity on the inner surface of the symphysis. Normally this distance is 11 cm.
What's happened
The pelvis as an anatomical formation is represented by two pelvic bones and the distal spine (sacrum and coccyx). In obstetrics, only that part of it that is called the small pelvis is important. This is the space limited by the lower sections of the sacrum and coccyx. It contains the following organs: the bladder, uterus and rectum. There are four main planes in its structure. Each of them has several sizes that are important in obstetric practice.
Parameters of entry into the pelvis
- The size is straight. This indicator has other names - obstetric conjugate and true conjugate. Equal to 110 mm.
- Transverse size. Equal to 130-135 mm.
- The dimensions are oblique. Equal to 120-125 mm.
- Diagonal conjugate. Equal to 130 mm.
Parameters of the wide part of the small pelvis
- The size is straight. Equal to 125 mm.
- Transverse size. Equal to 125 mm.
Parameters of the narrow part of the small pelvis
Pelvic outlet parameters
- The size is straight. During childbirth, it may increase, as the fetal head moving along the birth canal bends the tailbone posteriorly. It is 95-115 mm.
- Transverse size. Equal to 110 mm.
Measuring the pregnant pelvis
The above indicators are anatomical, that is, they can be determined directly from the pelvic bones. It is not possible to measure them on a living person. Therefore, in obstetric practice the most important parameters are:
- The distance between the awns located at the anterior edge of the ridge.
- The distance between the points of the iliac crests that are separated from each other by the maximum distance.
- The distance between the protrusions of the femurs in the area where their upper part transitions to the neck.
- (distance from to the lumbosacral cavity).
Thus, the normal dimensions of the pelvis are 250-260, 280-290, 300-320 and 200-210 millimeters, respectively.
Clarification of these parameters is mandatory when registering a pregnant woman. The measurement is carried out with a special instrument (pelvic meter), which, by the way, can also be used to measure the head of a newborn baby.
It is important to understand that the volume of soft tissue does not affect the result of the study. The parameters of the pelvis are assessed by bony protrusions, and they do not shift anywhere when losing weight or, on the contrary, gaining weight. The size of the pelvis remains unchanged after a woman reaches the age when bone growth stops.
To diagnose pelvic narrowing, two more conjugates are important - true (obstetric) and diagonal. However, it is not possible to measure them directly; their size can only be judged indirectly. The diagonal conjugate in obstetrics is usually not measured at all. More attention is paid to the obstetric conjugate.
The determination of the true conjugate is carried out according to the formula: the size of the outer conjugate minus 9 centimeters.
What is a narrow pelvis?
Before talking about the definition of this term, it should be noted that there are two types of narrow pelvis - anatomical and clinical. These concepts, although not identical, are closely related to each other.
We should talk about an anatomically narrow pelvis when at least one of the parameters is smaller than the normal dimensions of the pelvis. There are degrees of narrowing when the true conjugate is less than normal:
- by 15-20 mm.
- 20-35 mm.
- 35-45 mm.
- more than 45 mm.
The last two degrees indicate the need for surgical intervention. A true conjugate of the 1st-2nd degree allows the possibility of continuing childbirth naturally, provided that there is no threat of a condition such as a clinically narrow pelvis.
Clinically, a narrow pelvis is a situation when the parameters of the fetal head do not correspond to the parameters of the mother’s pelvis. Moreover, all dimensions of the latter can be within normal limits (that is, from an anatomical point of view, this pelvis is not always narrow). The opposite situation may also occur, when an anatomically narrow pelvis completely corresponds to the configuration of the fetal head (for example, if the child is small), and in this case there is no question of a diagnosis of a clinically narrow pelvis.
The main reasons for this condition:
- On the maternal side: anatomically small pelvis, irregular pelvic shape (for example, deformation after injury).
- From the side of the fetus: hydrocephalus, large size, tilting of the head when the fetus enters the pelvis.
Depending on how pronounced the difference is between the parameters of the maternal pelvis and the fetal head, three degrees of clinically narrow pelvis are distinguished:
- Relative disparity. In this case, spontaneous childbirth is possible, but the doctor must be ready to make a timely decision on surgical intervention.
- Significant discrepancy.
- Absolute discrepancy.
Childbirth with a clinically narrow pelvis
The second and third degrees are an indication for surgery. Independent childbirth in this situation is impossible. The fetus can only be delivered by caesarean section.
If there is a relative discrepancy, natural childbirth is acceptable. However, one should remember the danger of changing the situation for the worse. The doctor should consider the severity of the discrepancy during the period of contractions in order to promptly decide on further tactics. Delayed diagnosis of conditions when delivery should be resolved only surgically can lead to serious difficulties with the removal of the fetal head. If there is a pronounced discrepancy, the latter will be driven into the pelvic cavity by the contracting uterus, which will lead to severe head injury and death. In advanced cases, it is impossible to extract the fetus alive from the pelvic cavity even if a cesarean section is performed. In such cases, childbirth has to be completed with a fetal destruction operation.
Let's sum it up
It is necessary to know the size of the pelvis. This is necessary in order to promptly suspect such pathological conditions as an anatomically and clinically narrow pelvis. A decrease in normal size can be of varying degrees of severity. In some cases, spontaneous childbirth is even possible; in other situations, it becomes necessary to perform a cesarean section.
Clinically narrow pelvis is a very insidious condition. It is not always combined with the concept of an anatomically narrow pelvis. The latter may have normal parameters, but the possibility of a discrepancy between the size of the head and the size of the pelvis still exists. The occurrence of such a situation during childbirth can cause dangerous complications (first of all, the fetus will suffer). Therefore, timely diagnosis and quick decision-making on further tactics are so important.
The bony pelvis consists of a large and small pelvis. The border between them: behind is the sacral promontory; on the sides - innominate lines, in front - the upper part of the pubic symphysis.
The bony basis of the pelvis is made up of two pelvic bones: the sacrum and the coccyx.
The female pelvis is different from the male pelvis.
A large pelvis is not important in obstetric practice, but it is available for measurement. The shape and size of the small pelvis are judged by its size. An obstetric pelvisometer is used to measure the large pelvis.
Basic female pelvis sizes:
In obstetric practice, a fundamental role is played by the small pelvis, which consists of 4 planes:
- The plane of entry into the pelvis.
- The plane of the wide part of the small pelvis.
- The plane of the narrow part of the pelvic cavity.
- The plane of exit from the pelvis.
Plane of entry into the pelvis
Borders: behind - the sacral promontory, in front - the upper edge of the pubic symphysis, on the sides - innominate lines.
Direct size is the distance from the sacral promontory to the upper edge of the false articulation 11 cm. The main size in obstetrics is coniugata vera.
The transverse size is 13 cm - the distance between the most distant points of the nameless lines.
Oblique dimensions are the distance from the sacroiliac joint on the left to the false protrusion on the right and vice versa - 12 cm.
The plane of the wide part of the pelvis
Borders: in front - the middle of the false articulation, behind - the junction of the 2nd and 3rd sacral vertebrae, on the sides - the middle of the acetabulum.
It has 2 sizes: straight and transverse, which are equal to each other - 12.5 cm.
Straight size is the distance between the gray area of the pubic symphysis and the junction of the 2nd and 3rd sacral vertebrae.
The transverse dimension is the distance between the middles of the acetabulum.
The plane of the narrow part of the pelvic cavity
Borders: in front - the lower edge of the pubic symphysis, behind - the sacrococcygeal joint, on the sides - the ischial spines.
Direct size is the distance between the lower edge of the pubic symphysis and the sacrococcygeal joint - 11 cm.
The transverse dimension is the distance between the ischial spines - 10.5 cm.
Plane of exit from the pelvis
Borders: in front - the lower edge of the symphysis pubis, in the back - the apex of the coccyx, on the sides - the inner surface of the ischial tuberosities.
Straight size is the distance between the lower edge of the symphysis and the tip of the coccyx. During childbirth, the fetal head deviates the coccyx by 1.5-2 cm, increasing the size to 11.5 cm.
Transverse size - the distance between the ischial tuberosities - 11 cm.
The pelvic inclination angle is the angle formed between the horizontal plane and the plane of the entrance to the pelvis, and is 55-60 degrees.
The wire axis of the pelvis is a line connecting the vertices of all straight dimensions of the 4 planes. It is not shaped like a straight line, but concave and open at the front. This is the line along which the fetus passes when it is born through the birth canal.
Pelvic conjugates
External conjugate – 20 cm. Measured with a pelvic meter during an external obstetric examination.
Diagonal conjugate – 13 cm. Measured by hand during internal obstetric examination. This is the distance from the lower edge of the symphysis (inner surface) to the sacral promontory.
The true conjugate is 11 cm. This is the distance from the upper edge of the symphysis to the sacral promontory. Not measurable. It is calculated by the size of the outer and diagonal conjugate.
According to the external conjugate:
9 is a constant number.
20 – external conjugate.
Along the diagonal conjugate:
1.5-2 cm is the Solovyov index.
The thickness of the bone is determined around the circumference of the wrist joint. If it is 14-16 cm, then 1.5 cm is subtracted.
If 17-18 cm, 2 cm is subtracted.
Michaelis's rhombus is a diamond-shaped formation located on the back.
It has dimensions: vertical – 11 cm and horizontal – 9 cm. In total (20 cm), giving the size of the external conjugate. Normally, the vertical size corresponds to the size of the true conjugate. The condition of the small pelvis is judged by the shape of the diamond and its size.
Table of contents of the topic "The pelvis from an obstetric point of view. Physiology of the female reproductive system.":2. Dimensions of the plane of the wide part of the small pelvis. Dimensions of the plane of the narrow part of the small pelvis.
3. Wired pelvic axis. Pelvic inclination angle.
4. Physiology of the female reproductive system. Menstrual cycle. Menses.
5. Ovaries. Cyclic changes in the ovaries. Primordial, preantral, antral, dominant follicle.
6. Ovulation. Yellow body. Female hormones synthesized in the ovaries (estradiol, progesterone, androgens).
7. Cyclic changes in the uterine mucosa (endometrium). Proliferation phase. Secretion phase. Menstruation.
8. The role of the central nervous system in the regulation of menstruation. Neurohormones (luteinizing hormone (LH), follicle-stimulating hormone (FSH).
9. Types of feedback. The role of the feedback system in the regulation of menstrual function.
10. Basal temperature. Pupil symptom. Karyopyknotic index.
Big pelvis for the birth of a child is not significant. The bony basis of the birth canal, which represents an obstacle to the fetus being born, is the small pelvis. However, by the size of the large pelvis one can indirectly judge the shape and size of the small pelvis. The inner surface of the large and small pelvis is lined with muscles.
Rice. 2.7. Female pelvis (sagittal section).1 - anatomical conjugate;
2 - true conjugate;
3 - direct dimension of the plane of the wide part of the pelvic cavity;
4 - direct dimension of the plane of the narrow part of the pelvic cavity;
5 - direct size of the pelvic outlet with the normal position of the coccyx;
6 - direct size of the pelvic outlet with the tailbone bent posteriorly;
7 - wire axis of the pelvis.
Pelvic cavity is the space enclosed between the walls of the pelvis, limited above and below by the planes of inlet and outlet of the pelvis. It has the appearance of a cylinder, truncated from front to back, with the front part facing the womb almost 3 times lower than the back part facing the sacrum. Due to this shape of the pelvic cavity, its various parts have different shapes and sizes. These sections are imaginary planes passing through identification points of the inner surface of the pelvis. In the small pelvis, the following planes are distinguished: the entrance plane, the wide part plane, the narrow part plane and the exit plane (Table 2.1; Fig. 2.7).
Plane of entry into the pelvis passes through the upper inner edge of the pubic arch, the innominate lines and the apex of the promontory. In the entrance plane, the following dimensions are distinguished (Fig. 2.8).
Straight size- the shortest distance between the middle of the upper inner edge of the pubic arch and the most prominent point of the cape. This distance is called true conjugata (conjugata vera); it is equal to 11 cm. It is also customary to distinguish the anatomical conjugate - the distance from the middle of the upper edge of the pubic arch to the same point of the promontory; it is 0.2-0.3 cm longer than the true conjugate (see Fig. 2.7).
Transverse size- the distance between the most distant points of the nameless lines of opposite sides. It is equal to 13.5 cm. This size intersects the true conjugate at a right angle eccentrically, closer to the cape.
Rice. 2.8. Dimensions of the plane of entry into the small pelvis.
1 - direct size (true conjugate);
2 - transverse size;
3 - oblique dimensions.
Oblique dimensions - right and left. The right oblique dimension goes from the right sacroiliac joint to the left iliopubic tubercle, and the left oblique dimension goes from the left sacroiliac joint to the right iliopubic tubercle. Each of these sizes is 12 cm.
As can be seen from the given dimensions, the entrance plane has a transverse oval shape.
The plane of the wide part of the pelvic cavity passes in front through the middle of the inner surface of the pubic arch, on the sides - through the middle of the smooth plates located under the fossae of the acetabulum (lamina acetabuli), and behind - through the articulation between the II and III sacral vertebrae.
Table 2.1 Planes and dimensions of the small pelvisSMALL PELVIS.
BIG PELIN
The large pelvis is much wider than the small one. Limited:
From the sides by the wings of the iliac bones,
Posteriorly – the last lumbar vertebrae,
In front - the lower part of the abdominal wall.
The pelvis is the bony part of the birth canal.
The posterior wall of the pelvis consists of:
Sacrum and coccyx,
The lateral ones are formed by the ischial bones,
anterior – pubic bones and symphysis
Pelvic sections:
Cavity
In the pelvic cavity there are a wide and a narrow part.
In accordance with this, four planes of the pelvis are considered:
I – plane of entrance to the pelvis,
II – plane of the wide part of the pelvic cavity,
III – plane of the narrow part of the pelvic cavity,
IV – plane of exit of the pelvis.
I. Plane of entry into the pelvis has the following boundaries:
In front - the upper edge of the symphysis and the upper inner edge of the pubic bones,
On the sides there are nameless lines,
Behind is the sacral promontory.
The entrance plane has the shape of a kidney or a transverse oval with a notch corresponding to the sacral promontory.
There are three sizes at the entrance to the pelvis:
Transverse,
Two obliques.
Straight size– the distance from the sacral promontory to the most prominent point on the inner surface of the symphysis pubis. This size is called obstetric, or true conjugate(conjugata vera). There is also an anatomical conjugate - the distance from the promontory to the middle of the upper inner edge of the symphysis; the anatomical conjugate is slightly (0.3-0.5 cm) larger than the obstetric conjugate. Obstetric, or true conjugate is 11 cm.
Transverse size– the distance between the most distant points of nameless lines. This size is 13-13.5 cm.
Oblique dimensions: right and left, which are equal to 12-12.5 cm.
Right oblique dimension - the distance from the right sacroiliac joint to the left iliopubic tubercle,
The left oblique dimension is from the left sacroiliac joint to the right iliopubic tubercle.
II. The plane of the wide part of the pelvic cavity has the following boundaries:
in front - the middle of the inner surface of the symphysis,
on the sides - the middle of the acetabulum,
behind – the junction of the II and III sacral vertebrae.
In the wide part of the pelvic cavity, two sizes are distinguished: straight and transverse.
Straight size - from the junction of the II and III sacral vertebrae to the middle of the inner surface of the symphysis; equals 12.5 cm.
Transverse size – between the tips of the acetabulum; equals 12.5 cm.
There are no oblique dimensions in the wide part of the pelvic cavity because in this place the pelvis does not form a continuous bone ring. Oblique dimensions in the widest part of the pelvis are conditionally allowed (length 13 cm).
III. The plane of the narrow part of the pelvic cavity limited:
anteriorly by the lower edge of the symphysis,
from the sides - the spines of the ischial bones,
behind – the sacrococcygeal joint.
There are two sizes: straight and transverse.
Straight the size goes from the sacrococcygeal joint to the lower edge of the symphysis (apex of the pubic arch); equal to 11-11.5 cm.
Transverse size connects the ischial spines; equal to 10.5 cm.
IV. Pelvic exit plane has the following boundaries:
In front - the lower edge of the symphysis,
From the sides - the ischial tuberosities,
At the back is the tip of the coccyx.
There are two sizes of the pelvic outlet: straight and transverse.
Straight the size of the pelvic outlet goes from the top of the coccyx to the lower edge of the symphysis; it is equal to 9.5 cm. When the fetus passes through the small pelvis, the tailbone moves away by 1.5-2 cm and the direct size increases to 11.5 cm.
Transverse the size of the pelvic outlet connects the internal surfaces of the ischial tuberosities; = 11 cm.
FEMALE PELVIS from an obstetric point of view.
The bony pelvis consists of two pelvic bones, the sacrum and the coccygeal bone, which are firmly connected through cartilaginous layers and connections.
The pelvic bone is formed from the fusion of three bones: longitudinal, ischial and pubic. They connect at the acetabulum.
The sacrum consists of 5-6 motionlessly connected vertebrae that merge into one bone.
The coccygeal bone consists of 4-5 underdeveloped vertebrae.
The bony pelvis in the upper section is open forward. This part is called the large pelvis. Bottom part- this is a closed bone formation - the small pelvis. The border between the large and small pelvis is the terminal (nameless) line: in front - the upper edge of the symphysis and pubic bones, on the sides - the arcuate lines of the ilium, behind - the sacral prominence. The plane between the large and small pelvis is the entrance to the small pelvis. The large pelvis is much wider than the small pelvis, it is limited on the sides by the wings of the ilium, behind by the last lumbar vertebrae, and in front by the lower part of the anterior abdominal wall.
All women have their pelvis measured. There is a relationship between the sizes of the large and small pelvis. By measuring a large pelvis, we can draw conclusions about the size of a small one.
Normal sizes of the female pelvis:
- distantia spinarum - the distance between the anterior upper bones of the longitudinal bone - 25-26 cm;
- distantia cristarum - the distance between distant points of the iliac crests - 28-29 cm;
- conjugata externa - (external conjugate) - the distance from the middle of the upper edge of the symphysis to the upper corner of the Michaelis rhombus (measurements are carried out with the woman lying on her side) - 20-21 cm.
Michaelis rhombus- this is an expansion of the depression in the sacral region, the limits of which are: above - the fossa under the spinous process of the fifth lumbar vertebra (supracrigian fossa), below - the points corresponding to the posterosuperior spine of the iliac bones. The average length of a rhombus is 11 cm, and its diameter is 10 cm.
Diagonal conjugate— the distance from the lower edge of the symphysis to the most protruding point of the promontory of the sacral bone is determined during vaginal examination. With normal pelvic sizes it is 12.5-13 cm.
The size of the true conjugate (direct size of the entrance to the small pelvis) is determined by subtracting 9 cm from the length of the external conjugate or subtracting 1.5-2 cm from the length of the diagonal conjugate (depending on the Solovyov index).
Solovyov index - the circumference of the wrist-carpal joint, divided by 10. The index allows you to have an idea of the thickness of a woman’s bones. The thinner the bones (index = 1.4-1.6), the greater the capacity of the small pelvis. In these cases, 1.5 cm is subtracted from the diagonal conjugate to obtain the length of the true conjugate. With the Solovyov index
I, 7-1.8 - subtract 2 cm.
Pelvic tilt angle — the angle between the plane of the entrance to the small pelvis and the horizon is 55-60 °. Deviations in one direction or another can negatively affect the course of labor.
The normal height of the symphysis is 4 cm and is measured with the index finger during vaginal examination.
Pubic angle - with normal pelvic sizes is 90-100 °.
Small pelvis - This is the bony part of the birth canal. The posterior wall of the small pelvis consists of the sacrum and coccyx, the lateral ones are formed by the ischium, and the anterior wall is formed by the pubic bones and the symphysis. The small pelvis has the following sections: inlet, cavity and outlet.
In the pelvic cavity there are wide and narrow parts. In this regard, four planes of the pelvis are determined:
1 - plane of entrance to the small pelvis.
2 - plane of the wide part of the pelvic cavity.
3 - plane of the narrow part of the pelvic cavity.
4 - plane of exit from the pelvis.
The plane of entry into the pelvis passes through the upper inner edge of the pubic arch, the innominate lines and the apex of the promontory. The following dimensions are distinguished in the entrance plane:
- Direct size - the distance from the sacral protrusion to the point that most protrudes on the upper inner surface of the symphysis - this is the obstetric, or true conjugate, equal to 11 cm.
- Transverse size is the distance between the distant points of the arcuate lines, which is 13-13.5 cm.
- Two oblique dimensions - from the iliosacral junction on one side to the iliopubic tubercle on the opposite side of the pelvis. They are 12-12.5 cm.
The plane of the wide part of the pelvic cavity passes through the middle of the inner surface of the pubic arch, on the sides through the middle of the trochanteric cavity and behind - through the connection between the II and III sacral vertebrae.
In the plane of the wide part of the small pelvis there are:
- Direct size - from the middle of the inner surface of the pubic arch to the junction between the II and III sacral vertebrae. It is 12.5 cm.
- The transverse dimension runs between the middles of the acetabulum. It is 12.5 cm.
The plane of the narrow part is through the lower edge of the pubic junction, on the sides - through the gluteal spines, behind -
through the sacrococcygeal joint.
In the plane of the narrow part they are distinguished:
1. Straight size - from the lower edge of the symphysis to the sacrococcygeal joint. It is equal to II.5cm.
2. Transverse size between distant points of the inner surface of the ischial spines. It is equal to 10.5 cm.
The plane of exit from the small pelvis passes in front through the lower edge of the symphysis, from the sides - through the tops of the gluteal tuberosities, and from behind - through the crown of the coccyx.
In the plane of exit from the small pelvis there are:
1. Straight size - from the tip of the coccyx to the lower edge of the symphysis. It is equal to 9.5 cm, and when the fetus passes through the pelvis it increases by 1.5-2 cm due to the deviation of the apex of the coccyx of the presenting part of the fetus.
2. Transverse size - between distant points of the internal surfaces of the ischial tuberosities; it is equal to 11cm.
The line connecting the midpoints of the straight dimensions of all planes of the pelvis is called the leading axis of the pelvis, and has the shape of a concave line forward. It is along this line that the leading point passes through the birth canal.
The main differences between the female and male pelvis:
- The bones of the female pelvis are thin and smooth;
- The female pelvis is relatively wider, lower and larger in volume;
- The wings of the ilium in women are more developed, so the transverse dimensions of the female pelvis are larger than those of men;
- The entrance to the pelvis of a woman has a transverse oval shape, and in men it has the shape of a card heart;
- The entrance to the small pelvis in women is larger and the pelvic cavity does not narrow downward into a funnel-shaped cavity, as in men;
- The pubic angle in women is obtuse (90-100°), and in men it is acute (70-75°);
- The pelvic tilt angle in women is greater (55-60°) than in men (45°).
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