Theories of Labor Onset Labor is a coordinated sequence of involuntary, intermittent uterine contractions. It is the series of events that expels the fetus and placenta out of of the mother¶s body. This is made possible possible by the presence of uterine contractions and abdominal pressure that push the fetus out during the expulsion period of delivery. Regular contractions result to gradual cervical effacement and dilatation. Adequate pressure from abdominal muscles allows the baby to be pushed outside the mother¶s womb. Labor and delivery require a woman to utilize her coping methods psychologically and physiologically. Normally, labor begins when the fetus reaches a mature age (38-42 weeks age of gestation). This is to ensure survival of the fetus with the extrauterine life. The mechanism that converts Braxton Hicks Contractions (painless contractions) to strong and coordinated uterine contractions is unknown. In some cases, labor occurs before the fetus reaches the mature age (preterm birth) while in others it is delayed (postterm birth). Although the exact mechanism that initiates labor is unknown. Theories have been proposed to explain how and why labor occurs. Stretch theory The idea is based on the co ncept that any hollow body organ when stretched to its capacity will inevitably contract to expel its contents. The uterus, which is a hollow muscular organ, becomes stretched due to the growing fetal structures. In return, the pressure increases causing physiologic changes (uterine contractions) that initiate labor.
Uterine
Oxytocin theory Pressure on the cervix stimulates the hypophysis to release oxytocin from the maternal posterior pituitary gland. As pregnancy advances, the uterus becom es more sensitive to oxytocin. Presence of this hormone causes the initiation of contraction of the smooth muscles of the body (uterus is composed of smooth muscles).
deprivation theory Progesterone is the hormone designed to promote pregnancy. It is believed that presence of this hormone inhibits uterine motility. As pregnancy advances, changes in the relative effects estrogen and progesterone encourage the onset of labor. A marked increase in estrogen level is noted in relation to progesterone, making the latter hormone less effective in controlling rhythmic uterine contractions. Also, in later pregnancy, rising fetal cortisol levels inhibit progesterone production from the placenta. Reduce progesterone formation initiates labor.
Progesterone
Prostaglandin theory In the latter part of pregnancy, fetal membranes and uterine decidua increase prostaglandin levels. This hormone is secreted from the lower area of the fetal membrane (forebag). A decrease in progesterone amount also elevates the prostaglandin level. Synthesis of prostaglandin, in return, causes uterine contraction thus, labor is initiated.
Theory of Aging Placenta Advance placental age decreases blood supply to the uterus. This event triggers uterine contractions, thereby, starting the labor.
SIGNS of LABOR
Preliminary/Prodromal
Signs of Labor
1. Ligthening ± setting of fetal head into pelvic brim occurs approximately 10-14 days before labor begins gives the woman relief from diaphragmatic pressure and shortness of breath occurs early in primiparas mother may experience: shooting leg pains from the increased pressure on the sciatic nerve, increased amounts of vaginal discharge and urinary frequency from pressure on the bladder 2. Increased in Level of Activity ± related to an increase in epinephrine release that is initiated by a decrease in progesterone produced by the pl acenta 3. Braxton Hicks Contractions ± painless irregular contractions, sometimes strong that may cause discomfort 4. Ripening of the cervix ± Goodell¶s sign: the cervix feels softer than normal similar to earlobe throughout pregnancy; at term cervix is described butter-soft Signs of TR UE LABOR:
1. Uterine Contractions ± surest sign that labor has begun 2. Show ± the blood mixed with mucus, takes on a pink tinge. It is when mucus plug is expelled and capillaries are exposed. 3. Rupture of the membranes ± experienced either as a sudden gush or as a scanty, slow seeping of clear fluid from the vagina. False Labor:
Irregular contractions Pain is confined to the abdominal No increase in duration, frequency, and intensity. Pain disappears with ambulating No cervical change Sedation stops contractions
True Labor:
Regular contractions Pain on the lower back to the abdomen Increase in duration, frequency and intensity Pain not relieved upon ambulating Accompanied with effacement and dilatation Sedation does not stop contraction
CHARACT ERISTICS
1. 2.
of CONTRACTIONS
Mild ± uterine muscle are somewhat tense but can be indented by a gentle pressure Moderate ± uterus is moderately firm and a firmer pressure is needed to indent
3.
Strong ± the uterus becomes very firm that at the height of contraction cannot be indented.
COMPONENTS
1.
of LABOR
Passage ± refers to the shape and measurement of maternal pelvis and distensibility of birth canal refers to the route a f etus must travel from the uterus through the cervix and vagina to the external perineum. Elastic to expand and accommodate 4 Basic Classification of Pelvis: a. Gynecoid ± best pelvis; half of the population b. Android ± common in men, 20% in women; heart shape and difficult for vaginal delivery c. Anthropoid ± common in men; 20-30%, pelvic inlet oval d. Platypelloid ± flat pelvis; least common; 5% of the population, long sacrum
2.
Passenger ± refers to the fetus, its size, presentation, and position.
3.
Power ± forces acting together to expel fetus from the uterus 2 TYPES of POWER
a. Primary Powers ± involuntary contractions of the uterus b. Secondary Powers- voluntary bearing down efforts of the mother
4. Psyche ± reflects the woman¶s frame of mind in dealing with the labor experience Structure of the fetal skull
Cranium ± uppermost portion of the skull, comprises eight bones. - the four bones: the frontal (actually 2 fused bones), 2 parietal and occipital. - The other four: sphenoid, ethmoid, and 2 temporal bones
The Suture Lines:
Sagittal suture- joins the 2 parietal bones of the skull Coronal suture ± the line of juncture of the f rontal bones and the 2 parietal bones Lambdoid suture ± the line of juncture of the occipital bone and 2 parietal bones.
Fontanelles: - significant membrane-covered spaces that are f ound at the junction of the main suture lines
Anterior Fontanelle ± referred to as bregma; lies at the junction of the coronal and sagittal sutures
-
diamond-shape anteroposterior diameter is 3-4cm transverse diameter is 2-3cm
Posterior Fontanelle ± lies at the junction of the lambdoidal and sagittal sutures.
-
triangular smaller than the anterior Fontanelle only 2cm across its widest part
Vertex ± the space between two fontanelles Sinciput ± the area over the frontal bone Occiput ± the area over the occipital bone
Suboccipitobregmatic ± narrowest diameter 9.5cm; from the inferior aspect of the occiput to the center of the anterior fontanelle
Occipitofrontal ± measured from the bridge of the nose to the occipital prominence is 12cm
Occipitomental ± the widest which is 13.5cm; measured from the chin to the posterior fontanelle
Molding ± the change in shape of t he fetal skull produced by the force of uterine contractions pressing the vertex of the head against the not-yet-dilated cervix.
FETAL
PRESENTATION
and
POSITION
Attitude ± describes the degree of flexion a fetus assumes during labor or the relation of fetal parts to each other
1) Good Attitude (complete flexion) ± the spinal column is bowed forward that the chin touches the sternum, the arms are flexed and folded on chest, the thighs are flexed onto the abdomen and the calves are pressed against the posterior aspect of the thighs. 2) Moderate flexion ± the chin is not touching the chest but is in an alert or military position 3) Poor flexion ± the back is arched, the neck in extended and a fetus is in complete extension, presenting the occipitomental diameter of the head to the birth canal (face presentation) Engagement ± refers to the settling of t he presenting part of a fetus f ar enough into the pelvis to be at the level of the ischial spines.
Floating ± a presenting part that is not engaged Dipping ± one that is descending but has not yet reached the ischial spines
Station ± refers to the relationship of the presenting part of a f etus to the level of ischial spines
0 station ± presenting part of a fetus is at the level of the ischial spines -4 station ± head is at outlet +4 station ± head is floating
FETAL LIE ± the relationship between the long axis of the body and the long axis of a woman¶s body
2 Primary Lie 1. Longitudinal 2. Transverse
FETAL PRESENTATIONS ± denote the body part that will first contact the cervix of be born first. - this is determined by a c ombination of fetal lie and the degree of flexion
3 Main Presentations
a. Cephalic ± the fetal head is the body part that will first contact the cervix - the four types of cephalic presentation: vertex, brow, face and mentum
b. Breech ± either the buttocks or the f eet are the first body part that will contact the cervix - the 3 type of breech presentation: complete, frank, and footling)
c. Shoulder ± the presenting part is usually one of the shoulders (acromion process, an iliac crest, a hand, or an elbow
POSITION ± the relationship of the presenting part to a specific quadrant of a woman¶s pelvis
UTERINE CONTRACTIONS:
Origins Labor contractions begin a ³pacemaker´ point located in the myometrium near one of the uterotubal junctions In some women, contractions appear to originate in the lower uterine segment rather than in the fundus.
Phases
3 Phases: increment, acme, decrement Increment- when the intensity of the contraction increases Acme- when the contraction is at its strongest Decrement- when the intensity decreases As labor progresses the relaxation intervals decrease from 10 minutes to 2 ± 3 minutes The duration also changes from 20-30 sec to a range of 60-90 sec
Contour Changes
Upper segment becomes thicker and active, preparing it to be able to exert the strength necessary to expel the fetus when the ex pulsion phase of labor is reached The lower segment becomes thin-walled, supple, and passive so that the fetus can be pushed out of the uterus easily Physiologic retraction ring ± a ridge on the inner uterine surface that marks the boundary between the 2 portions Pathologic retraction ring (Bandl¶s ring) ± it is a danger sign that signifies impending rupture of the lower uterine segment if the obstruction to labor is not relieved
Cervical Changes
Effacement
Shortening and thinning of the cervical canal Normally the canal is 1-2cm With effacement the canal virtually disappears because of longitudinal traction from the contracting uterine fundus
Dilation
Refers to the enlargement or widening of the cervical canal from an opening of few millimeters wide to one large enough (10cm). First reason why dilation occurs is uterine contractions gradually increase the diameter of the cervical canal lumen by pulling the cervix up ov er the presenting part of the fetus Second, the fluid-filled membranes press against the cervix As dilation begins there is large amount of vaginal secretions (show) because the last of the operculum or mucus plug in the cervix is dislodged and capillaries in the cervix rupture
