It is divided into three parts – inlet, cavity and outlet (Figure 1). The true pelvis is shallow anteriorly, formed by the symphysis pubis (4–5 cm), and deep posteriorly, formed by the sacrum and coccyx (10 cm). The significance of the false pelvis is to support the pregnant uterus the true pelvis is a bony passage for fetus to pass during labor. The pelvic brim extends from the sacral promontory, along the ilium on each side circularly along the ridge divides the pelvis into upper false pelvis and lower true pelvis. The bones are articulated together by four joints: anteriorly symphysis pubis, two sacroiliac joints posteriorly and the sacrococcygeal joint inferiorly. The maternal pelvis is made of five bones (Figure 1): the sacrum and coccyx posteriorly, two innominate bones on each side, and the pubic bone anteriorly. Maternal pelvis (passage)īony pelvis: ilium, ischium, pubis, sacrum and coccyx. 2, 3, 4 MECHANISM OF NORMAL LABORįor a successful normal labor a coordinated interaction of the uterine activity (power), maternal pelvis (passage) and fetus (passenger) is required. The onset of labor is also associated with an increase in prostaglandin production in the placental and cervix, furthering inducing their receptors and facilitating cervical ripening (PGE 2) and uterine contractions (PGF 2a). 1 This potentiates oxytocin receptors in the myometrium, reduces the progesterone/estrogen ratio and upregulates myometrial gap junctions to facilitate uterine contractions. Fetal dehyroepiandrosterone sulfate (DHEAS) is converted to estriol and estradiol by the placenta. Complex interactions of hormones between uterus, placenta and fetus. The factors that trigger labor at term are not clearly understood it is postulated that it is a result of changes in the hypothalamic–pituitary–adrenal axis, increasing fetal cortisol, and placental enzymatic functions. World Health Organization defines normal labor as starting spontaneously at term (37 completed weeks of gestation) for a fetus with cephalic presentation, progressing without maternal or fetal complication, and resulting in the delivery of fetus followed by placenta and membranes. The mechanism of normal labor is series of events that take place in the genital organ that allow the birth of a viable fetus at term followed by expulsion of placenta and membrane from the vagina. 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
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