Can abnormal pelvic tilt lead to dystocia?

The pelvic tilt is the angle between the pelvic inlet plane and the ground when a woman stands flat on the ground. The normal pelvic tilt is 60 degrees. ~70. The height difference between the sacral promontory and the upper edge of the pubic symphysis is 9.5 to 10 cm. A pelvic tilt within a certain normal range is conducive to smooth delivery. In the absence of other obstetric complications and birth canal abnormalities, pregnant women can usually give birth normally vaginally.

Factors that cause excessive pelvic tilt:

1. Genetic factors: If one parent is born with a body shape that is too tilted pelvis, their children may have a similar or identical body shape.

2. Environmental factors When the pelvis is not yet mature, especially during the pelvic development stage (15 to 25 years old), unreasonable body position, posture, and gait can cause deformation of the pelvis through the action of the three forces of body gravity, the inward and upward support of the lower limbs, and the cohesive force of the pubic symphysis, leading to abnormal pelvic tilt. For example, the professional ballet dancers and women who wear high heels too early mentioned above, the reason for the increase in pelvic tilt is directly related to women wearing high heels for a long time during the stage of pelvic maturation.

Diagnosis of excessive pelvic tilt:

1. Long history of wearing high heels or practicing ballet professionally.

2. Physical signs: ① The pregnant woman's abdominal skin is loose, the uterus is overly protruding and tilted forward, presenting a hanging abdomen; ② The junction of the lumbar sacral cone on the pregnant woman's back is deeply sunken inward, and the sacrum is upturned; ③ The pubic symphysis is low, and when the pregnant woman is in a supine position, the lower edge of the pubic symphysis is 1 to 2 cm lower than that of a normal pregnant woman; ④ Most patients have high arch deformities in both feet and well-developed gastrocnemius muscles in both lower limbs.

3. Physical examination: ① Abdominal examination may show a positive trans-pubic sign. However, when the fetal head is pressed by hand, or the pregnant woman's position is changed to a semi-recumbent position with both lower limbs flexed, or the pregnant woman lies supine with both lower limbs flexed as far as possible toward the abdominal wall, the trans-pubic sign becomes negative, indicating that the fetal head cannot adapt to the angle of the pelvic population plane; ② The pregnant woman lies flat on a hard bed. If the examiner's fist can pass between the pregnant woman's lumbar sacral part and the bed surface, it should be highly suspected that the pelvic tilt is too large; ③ The pregnant woman stands upright, with a vertical hanging line placed in the middle of the back below the buttocks. The distance from the line to the skin measured at the level of the lumbar sacral joint should be more than 5 cm.

4. Pelvic measurement: X-rays are performed before or during late pregnancy to observe the pelvic shape and to rule out other pelvic abnormalities such as a flat pelvis or a deformed pelvis. Alternatively, use a Martin's external pelvic measuring device to measure the sacral pubic external diameter and read the pelvic tilt at the same time.

Prevention and treatment: For acquired abnormal pelvic tilt, the most important thing is prevention. During the period of pelvic development, try to wear flat shoes, pay attention to correcting incorrect walking and standing postures, strengthen nutrition, supplement calcium, avoid single physical exercise, and ensure the normal development of the pelvis. Pregnant women with excessive pelvic tilt should try to adopt a semi-recumbent position starting 2 to 4 weeks before the expected date of delivery to increase the chance of the fetal head entering the pelvis. During delivery, the mother should also adopt a semi-recumbent position, or flex both lower limbs as much as possible to correct the pelvic tilt to normal so that the fetus can pass through the pelvic population plane smoothly.

It is particularly important to note that when the pelvic tilt is >70°, the pelvic tilt is too large. The sacrum shifts forward and upward, the pubic arch shifts backward and downward, and the position of the pubic symphysis is lowered, resulting in a shortening of the effective anterior-posterior diameter of the pelvis and a deviation of the birth axis from the normal direction, which affects the fetal delivery mechanism.