![]() After having entered the maternal bony pelvis in either an oblique or transverse diameter, in view of the narrow anteroposterior diameter at the pelvic inlet as a result of the projecting sacral promontory, the human fetus has to undergo an “internal rotation” in the larger “mid cavity” of the maternal pelvis. The evolutionary changes in the diameters of the human pelvis necessitated by the assumption of the erect posture by our human ancestors, have had a direct impact on the fetus during second stage of labor. Note the larger transverse diameter at the inlet (black arrow) as compared to the outlet (blue arrow). ![]() In contrast, due to the projection of the large ischial tuberosities, as a result of the need to provide attachments to the powerful muscles of thigh which were essential for running and hunting, the pelvic outlet has developed a smaller transverse diameter (Figure 1). The female bony birth canal is no longer cylindrical, but, has a narrower anteroposterior diameter at the level of the pelvic inlet due to the projection of the sacral promontory to aid weight-bearing. Unlike other “four-legged” mammals, the human pelvis has undergone significant evolutionary changes in view of the erect posture. It is important to appreciate that the pelvis is richly supplied by a network of blood vessels with significant anastomoses, as well as nerve fibers and nerve plexuses. The latter is composed of ligaments, muscles of the pelvic floor and of the pelvic sidewall, and the muscles of the perineum covered by the skin and subcutaneous tissue. The maternal birth passage consists of a bony pelvis comprising of the ilium, the ischium and the pubis, articulating with the sacrum and the coccyx posteriorly, as well as the soft tissues. This chapter addresses the anatomy of the female pelvis, mechanism of labor, fetal monitoring specific to the second stage of labor, the conduct of operative vaginal births and measures to avoid complications. The second stage of labor is very important because it is associated with increased maternal and perinatal morbidity and mortality as a result of the rapidity of onset of hypoxic stress to the fetus, as well as perineal trauma to the mother owing to the mechanical forces operating during the final stages of labor as the hand and bony fetal head traverse the maternal soft tissues that comprise the birth canal. It is further divided into a “passive” phase which involves a progressive descent and rotation of the presenting part, and an ”active” phase of maternal expulsive efforts. The second stage of labor refers to the period that elapses between the onset of full dilatation of the cervix, and delivery of the fetus. See end of chapter for details INTRODUCTION By completing 4 multiple-choice questions (randomly selected) after studying this chapter readers can qualify for Continuing Professional Development awards from FIGO plus a Study Completion Certificate from GLOWM
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |