Pelvic birth canal

Pelvic types sometimes have a significant impact on the delivery process. According to the pelvic entrance morphology of pelvic X-ray photography, pelvis can be divided into four types: female type, male type, anthropoid type and flat type. (pictured)

1. Female pelvis: This type belongs to normal pelvic morphology, accounting for about 52%-58.9% in China. The female pelvic entrance is round or oval, the edge of the back half is round, and the front half is round but wide. The posterior sagittal diameter of the entrance is slightly shorter than the anterior sagittal diameter. The pelvic side wall is straight down, the ischial spine is not prominent, the sacrum curvature is appropriate, and the ischial notch is wide and round, so the middle pelvis is wide.

2. Male pelvis: This kind of pelvis is relatively rare, accounting for about 1%-3.7% in China. The posterior part of male pelvis is nearly wedge-shaped, and the anterior part is also narrow triangle. The anterior sagittal diameter of the entrance is obviously longer than the posterior sagittal diameter. There is cohesion on both sides of the pelvis, and the ischial spine protrudes, so the middle part of the pelvis is narrow. The entire pelvis is funnel-shaped. In the process of delivery, the fetal head often enters the basin in occipital transverse position or uneven inclination, which is easy to cause persistent occipital transverse position and outlet stenosis in the middle of pelvis, so there are more chances of dystocia.

3. Ape pelvis: This type of pelvis accounts for about 14.2%- 18% in China. Its characteristic is that the entrance is oval, but the first half is narrow, and the front and rear diameter of the entrance is longer than the transverse diameter. Both sides of the pelvis are adducted, the ischial notch is large, the ischial spine is prominent, the sacrum is straight and backward, and the posterior half exit is large. Therefore, the fetus can generally be delivered through the vagina.

4. Flat pelvis: This type of pelvis accounts for about 23.2%-29% in China. The transverse diameter of this type of pelvis entrance is the same as that of normal female pelvis, but the transverse diameter of the entrance is relatively short and long. Therefore, it is often difficult to connect the fetal head, and uneven inclination is often used. Once the fetal head enters the basin, the fetus can be delivered from the vagina because of the large middle pelvis and outlet.