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Chapter 15

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McGill University
NUR1 233
Sonia Elizabeth Semenic

Chapter 15: Labor and Birth Processes Factors affecting labor Passenger: fetus and placenta Passageway: birth canal Powers: contractions Position of mother Psychologic response Passenger Size of fetal head, fetal presentation, fetal lie, fetal attitude, fetal position Placenta: passenger too rarely impedes process of labor in normal vaginal birth exception is placental previa Size of fetal head o Fetal skull: two parietal bones, two temporal boens, frontal bone and occipital bone o Sutures: sagittal, lambodial, coronal, and frontal membranous unite fetal skull bones o Fontanels: membrane-filled spaces located where sutures intersect Anterior: larger diamond shaped 3cm x 2cm at junction of sagittal, coronal, and frontal sutures closes by 18 months after birth Posterior: smaller triangular shaped 1cm x 2cm at junction of sutures of two parietal bones and occipital bone - closes by 6-8 weeks after birth o Sutures and fontanels make skull flexible to accommodate the infant brain, which continues to grow for some time after birth o Molding: bones not firmly united slight overlapping of the bones or molding of shape of head after labor Provides adaptation to the various dimeters of the maternal pelvis Head assumes normal shape within 3 days after birth o During labor, after rupture of membranes, palpation of fontanels and sutures during vaginal examination reveals fetal presentation, position, and attitude o Shoulder: diameter smaller than skull, facilitating passage through the birth canal o Hips: circumference small enough as well Fetal presentation o Part of the fetus that enters the pelvic inlet first and leads through the birth canal during labor at term o 3 main presentations Cephalic: head first 96% - usually occiput When presenting part is occiput, the presentation is noted as vertex Breech: buttocks or feet first 3% - usually sacrum Shoulder: 1% - usually scapula o Factors that determine the presenting part: fetal lie, fetal attitude, extension or flexion of head Fetal lie o Relation of the long axis (spine) of fetus to the long axis (spine) of mother o Longitudinal lie (vertical): long axis of the fetus is parallel with the long axis of the mother Either cephalic or breech, depending on fetal strucuture that first enters the mothers pelvis o Transverse lie (horizontal or oblique): long axis of the fetus is at the right angle diagonal to the long axis of the mother Has to be C-section Oblique lie: long axis of the fetus is lying at an angle to the long axis of the mother less common and usually converts to a longitudinal or transverse lie during labor Fetal attitude o Relation of the fetal body parts to one another o Fetus assumes a characteristic posture (attitude) in utero partly because of the mode of fetal growth and partly because of the way the fetus conforms to the shape of the uterine cavity o General flexion: back of fetus is rounded so that chin flexed on chest, thighs flexed on abdomen, and legs flexed at knees arms crossed over thorax, and umbilical cord between arms and legs Deviations from this may cause difficulties during childbirth o Cephalic presentation: fetal head may be extended or flexed in a manner that presents a head diameter that exceeds the limits of the maternal pelvis, leading to prolonged labor, forceps or vacuum-assisted birth, or cesarean o Certain crtical diameters of head measured Biparietal diameter: 9.25cm at term is largest transverse diameter and an important indicator of fetal head size In a well-flexed cephalic presentation the bipariental diameter is the widest part of the head entering the pelvic inlet Anteroposterior diameters: many of them Suboccipitobregmatic diameter: smallest and most critical 9.5cm at term when head in complete flexion, this diameter allows fetal head to pass through true pelvis easily As head more extended, anteroposterior diameter widens and the head may not be able to enter the true pelvis Fetal position o Position is the relation of the presenting part (occiput (lower back of head), sacrum, mentum (chin), sinciput (front of head), vertex (back of head)), to the four quadrants of the mothers pelvis o Denoted by three-letter abbreviation o First letter: denotes the location of the presenting part in the right (R) or left (L) side of the pelvis o Middle letter: specific presenting part of the fetus (O for occiput, S for sacrum, M for mentum, and Sc for scapula) o Third letter: location of the presenting part in relation to the anterior (A), posterior (P) or transverse (T) portion of the maternal pelvis o Ex. ROA: occuput is the presenting part and is located in the right anterior quadrant of the maternal pelvis o Station: relation of the presenting part of the fetus to an imaginary line drawn between the maternal ischial spines and is a measure of the degree of descent of the presenting part of the fetus through the birth canal Placement of the presenting part is measured in cm above or below the ischial spines Lowermost portion of the presenting part is 1cm above spines: station is -1 Presenting part at the level of the spines: station is 0 Presenting part 1cm below the spines: station is +1 Birth is imminent when the presenting part is at +4/+5 Station of the presenting part should be determined when labor begins so that the rate of descent of the fetus during labor can be accurately determined o Engagement: used to indicate the largest transverse diameter of the presenting part (usually the biparietal diameter) has passed through teh maternal pelvic brim or inlet into the true pelvis and usually corresponds to station 0 Occurs in the weeks just before labor begins in nulliparas and may not occur before or during labor in multiparas Can be determined by abdominal or vaginal examination Passageway Composed of mothers rigid bony pelvis and the soft tissues of the cervix, pelvis floor, vagina, and introitus (external opening to the vagina) Maternal pelvis: plays greatest role in labor process because the fetus must successfully accommodate itself to the relatively rigid passageway o Its size and shape must be determined before labor begins Bony pelvis o Formed by fusion of the ilium, ischium, and sacral bones o Four pelvic joints: symphysis pubis, right and left sacroiliac joints, and the sacrococcygeal joint o Separated by brim, or inlet, into two parts False pelvis: part above the brim and plays no part in childbrearing True pelvis: part involved in birth, divided into 3 planes inlet or brim, midpelvis or cavity, and outlet Pelvic inlet: upper border of the true pelvis formed anteriorly by upper margins of the pubic bone, laterally by the iliopectineal lines along the innominate bones, and posteriorly by anterior, upper margin of the sacrum and sacral promontory Pelvic cavity: curved passage with a short anterior wall and a longer concave posterior wall bounded by the posterior aspect of the symphysis pubis, the ischium, a portion of the ilium, the sacrum, and the coccyx Pelvic outlet: lower border of the true pelvis it is ovoid, somewhat diamond shaped and bounded by the pubic arch anteriorly, the ischial tuberosities laterally, and the top of the coccyx posteriorly The latter part of pregnancy, the coccyx is movable o Pelvic canal varies in size and shape at various levels o The diameters at the plane of the pelvic inlet, midpelvis, and outlet, plus the axis of the birth canal determine whether vaginal birth is possible and the manner by which the fetus may pass down the birth canal o Subpubic angle: determines the type of pubic arch o The fetus must first pass beneath the pubic arch, a narrow subpubic angle is less accommodating than a rounded wide arch o 4 basic types of pelves are classified as follows: Gynecoid: classical female type most common, with major gynecoid pelvic features in 50% of all women Android: resembling male pelvis less common Anthropoid: resembling the pelvis of anthropoid apes less common Platypelloid: flat pelvis least common Mixed types of pelves are more common than are pure types o Assessment of bony pelvis can be performed during the first prenatal evaluation and need not be repeated if the pelvis is of adequate size and suitable shape o 3 trimester: examination
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