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MEASURING Pelvis Dimensions for Pregnant Women

The study of the pelvis is important in obstetrics because its structure and size have a decisive influence on the course and outcome of labor. Normal pelvis is one of the main conditions for the correct course of labor. Deviations in the structure of the pelvis, especially the reduction of its size, impede the course of labor or represent insurmountable obstacles for them. The study of the pelvis produced by inspection, palpation and measurement of its size. On examination, attention is paid to the entire pelvic region, but the lumbosacral rhombus (Michaelis rhombus) is of particular importance. The Michaelis rhombus is called the shape of the sacrum, which has the contours of the rhomboid area. The upper corner of the rhombus corresponds to the spinous process of the V lumbar vertebra, the lower corner to the top of the sacrum (the place of discharge of the gluteus maximus muscles), the lateral angles to the upper-posterior spine of the iliac bones. Based on the shape and size of the rhombus, it is possible to assess the structure of the bone pelvis, to detect its narrowing or deformation, which is of great importance in the management of labor. In a normal pelvis, the rhombus corresponds to the shape of a square. Its dimensions are: the horizontal diagonal of the rhombus is 10-11 cm, the vertical diagonal is 11 cm. With various pelvic constrictions, the horizontal and vertical diagonals will be of different sizes, with the result that the shape of the rhombus will be changed.

In an external obstetric study, measurements are made with a centimeter tape (the circumference of the wrist joint, the size of the Michaelis rhombus, the abdominal circumference and the height of the uterus bottom above the lap) and the obstetric compass (tazomer) to determine the size of the pelvis and its shape.

A centimeter tape measures the largest abdominal circumference at the level of the navel (at the end of pregnancy it is 90-100 cm) and the height of the uterus floor is the distance between the upper edge of the pubic symphysis and the bottom of the uterus. At the end of pregnancy, the height of the uterus floor is 32-34 cm. Measuring the abdomen and the height of the uterus floor above the chest allows the obstetrician to determine the gestational age, the estimated weight of the fetus, to identify violations of fat metabolism, polyhydramnios, and multiple births. According to the external dimensions of the large pelvis, one can judge the size and shape of the small pelvis. Measurement of the pelvis produce a tazomerom. Only some dimensions (pelvic outlet and additional measurements) can be made with a measuring tape. Four pelvis sizes are usually measured - three transverse and one straight. The patient is in the supine position, the obstetrician is sitting on the side of her and facing her. Distantia spinarum - the distance between the most distant points of the anteroposterior iliac bones (spina iliaca anterior superior) - is 25-26 cm. Distantia cristarum - the distance between the most distant points of the iliac scallops (crista ossis ilei) is 28-29 cm. Distantia trochanterica - the distance between the greater trochanter of the femur (trochanter major) is 31–32 cm. Conjugata externa (outer conjugate) - the distance between the spinous process of the V lumbar vertebra and the upper edge of the pubic symphysis is equal to 20-21 cm. The patient turns to measure the outer conjugates on the side, the underlying leg flexes at the hip and knee joints, and the one above it pulls. The button of the tazomer is placed between the spinous process of the V lumbar and I sacral vertebra (supracarpal fossa) in the back and in the middle of the upper edge of the pubic symphysis in front. The size of the outer conjugate can be judged on the size of the true conjugates.
The difference between the outer and the true conjugate depends on the thickness of the sacrum, the symphysis and the soft tissues. The thickness of bones and soft tissues in women is different, so the difference between the size of the outer and true conjugate does not always exactly correspond to 9 cm. To measure the thickness of the bones, use the measurement of the circumference of the wrist joint and the Solovyov index (1/10 of the circumference of the wrist joint). Thin bones are considered thin if the circumference of the wrist joint is up to 14 cm and thick, if the circumference of the wrist joint is more than 14 cm. Depending on the thickness of the bones with the same external dimensions of the pelvis, its internal dimensions may be different. For example, with an outer conjugate of 20 cm and a Solovyov circumference of 12 cm (Solovyov’s index is 1.2), you must subtract 8 cm from 20 cm and obtain the true conjugate value of 12 cm. With a Solovyov circumference of 14 cm, you must subtract 20 cm from 20 cm at 16 cm subtract 10 cm - the true conjugate will be 9 and 10 cm respectively. The true size of the conjugates can be judged by the vertical size of the sacral rhombus and the size of the Frank. The true conjugate can be more accurately determined by the diagonal conjugate. The diagonal conjugate (conjugata diagonalis) is the distance from the lower edge of the symphysis to the most prominent point of the cape (13 cm). Diagonal conjugate is determined by vaginal examination of a woman, which is produced with one hand. The direct size of the pelvic outlet is the distance between the middle of the lower edge of the pubic symphysis and the tip of the coccyx. During the examination, the pregnant woman lies on her back with her legs apart and half bent at the hip and knee joints. The measurement is carried out with a tazomer This size, equal to 11 cm, is more than true by 1.5 cm due to the thickness of the soft tissues. Therefore, it is necessary to subtract 1.5 cm from the resulting figure of 11 cm, we obtain the direct size of the exit from the pelvic cavity, which is equal to 9.5 cm. The transverse size of the pelvic outlet is the distance between the internal surfaces of the sciatic tubercles. The measurement is carried out with a special tazomer or a measuring tape, which is applied not directly to the ischial tubercles, but to the tissues covering them; therefore, it is necessary to add 1.5-2 cm (thickness of soft tissues) to the obtained sizes of 9-9.5 cm. Normally, the transverse size is 11 cm. It is determined in the position of the pregnant woman on the back, and she presses her legs to the stomach as much as possible. Oblique pelvic dimensions have to be measured with skewed basins. To identify pelvic asymmetry, the following oblique dimensions are measured: the distance from the anterior upper spine of one side to the posterior upper spine of the other side (21 cm); from the middle of the upper edge of the symphysis to the right and left posterior-upper spines (17.5 cm) and from the supercrescent fossa to the right and left anteroposterior spines (18 cm). Oblique dimensions of one side are compared with the corresponding oblique dimensions of the other. With a normal pelvic structure, the size of paired oblique sizes is the same. A difference greater than 1 cm indicates pelvic asymmetry. The lateral dimensions of the pelvis are the distance between the anteroposterior and posterior anterior iliac bones of the same side (14 cm), measured by its tazomer. The lateral dimensions must be symmetrical and not less than 14 cm. With a lateral conjugate of 12.5 cm, labor is not possible. The angle of inclination of the pelvis is the angle between the plane of the entrance to the pelvis and the plane of the horizon. In the standing position of a pregnant woman, it is equal to 45-50. Determined using a special device - tazouglomera.
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