CHPTER 18 DYSTOCIA 부산백병원 산부인과 R1 이은숙

ABNORMAL LABOR AND FETOPELVIC DISPROPORTION

Etiological classification of dystocia literally, difficult labor abnormally slow progress of labor m/c contemporary indication of primary c/sec Abnormalities of the expulsive forces Uterine forces insufficiently strong or inappropriately coordinated to efface & dilate the cervix (uterine dysfunction) Inadequate voluntary muscle effort during the second stage of labor Abnormalities of presentation, position, or development of the fetus Abnormalities of the maternal bony pelvis Abnormalities of the reproductive tract that form an obstacle to fetal descent

Dystocia Today, expression such as cephalopelvic disproportion and failure to progress are often used to describe these dysfunctional labor when cesarean delivery is necessary Cephalopelvic disproportion (CPD) Disparity between the dimensions of the fetal head and maternal pelvis to preclude vaginal delivery True CPD is rare and most CPD are due to malposition of the fetal head : asynclitism or extension of the bony diameters of the fetal head Inability to achieve vaginal delivery after reaching complete dilatation is a significant marker of true dystocia because it is likely to recur

Dystocia Failure to progress This term include lack of progressive cervical dilatation or lack of descent The CPD and failure to progress are not precise terms and we should use more Practical terms, such as protraction or arrest The woman must be in the active phase of labor to diagnose either of these disorders Active phase arrest in 5 % of term nulliparas, this incidence has not changed since the 1950s ( Freidman 1978, Handa and Laros 1993) Inadequate uterine contractions ( < 180 Montevideo units ) were diagnosed in 80 % of women with active-phase arrest

Overdiagnosis of dystocia CPD (cephalopelvic disproportion) Most disproportions are due to malposition of fetal head, or to ineffective uterine contracture Factors leading to increased use of c/sec for dystocia Incorrect diagnosis of dystocia Epidural analgesia Fear of litigation Obstetrician convenience Variability in the criteria for diagnosis – major determinant Almost 25% of the c/sec performed annually in the USA for the lack of progress were in women with cervical dilatation of only 0 to 3 cm

Labor Diagnosis The strict definition of labor - uterine contractions that bring about demonstrable effacement and dilatation of the cervix Recognizing its start to instruct the woman to quantify contractions for some specified period define labor onset as the clock time when painful contractions become regular : very subjective to define the onset of labor to begin at the time of admission to the labor unit Admission criteria ( by National Maternity Hospital in Dublin ) painful uterine contractions accompanied by any one of the following ; ruptured membranes bloody show complete cervical effacement : in US, 3-4 cm or greater

Normal labor Criteria of Normal Labor Concept of 3 functional divisions of labor by Friedman Preparatory division latent & acceleration phases sensitive to sedation & conduction analgesia little cervical dilatation occurs, but considerable changes take place in the ground substance of cervix (collagen & other connective tissue component) Dilatational division phase of maximum slope of cervical dilatation most rapid rate of dilatation occur  unaffected by sedation or conduction analgesia Pelvic division deceleration phase & second stage cardinal fetal movements in the cephalic presentation take place principally during this phase

Normal labor Pattern of Cervical Dilatation ; 2 phases of cervical dilatation Latent phase           subject to sensitive changes by extraneous factors          (sedation → prolongation,  myometrial stimulation → shortening) Active phase ① Acceleration phase        usually predictive of the outcome of a particular labor ② Phase of maximum slope       good measure of the overall efficiency of the machine ③ Deceleration phase     more reflective fetopelvic relationship            2nd stage of labor commences after complete cervical dilatation            → only progressive descent of fetal presenting part is available                 to assess the progress of labor

Latent Phase commences with maternal perception of regular contractions accompanied by progressive & slow cervical dilatation and ends at between 3 and 5 cm of dilatation Prolonged latent phase > 20 hr in the nullipara and > 14 hr in the parous woman Factors that affect duration of the latent phase excessive sedation or conduction analgesia poor cervical condition false labor Management : rest and strong sedatives -> 85 % begin active labor -> 10 % cease contractions -> 5 % recur an abnormal latent phase -> oxytocin stimulation Amniotomy was discouraged during this phase Fetal and Maternal Effect of prolongation : not influence morbidity and mortality

Active Labor A rapid change in the slope of cervical dilatation between 3 & 4 cm the mean duration of active phase labor in nulliparas was 4.9 hours the rate of dilatation 1.2 cm/hr is the minimum normal rate in the nullipara 1.5 cm/hr is the minimum normal rate in the multipara active labor phase abnormalities – m/c abnormalities of labor incidence : in nullipara, 25% vs in multipara, 15% classification : protraction, arrest (Friedman 1972) associated factors of active labor phase abnormalities . excessive sedation or conduction analgesia . fetal malposition (e.g., persistent occiput posterior) The majority of active phase disorders did not result in cesarean delivery -only about 2 % of the 500 women studies (Friedman 1955)

Abnormal labor pattern Diagnostic criteria Nulliparas Multiparas Prolongation disorder (Prolonged latent phase) > 20 hr >14hr Protraction disorders 1. Protracted active phase dilatation 2. Protracted descent < 1.2 cm/hr < 1.0 cm/hr < 1.5 cm/hr < 2 cm/hr Arrest disorders 1.Prolonged deceleration phase 2. Secondary arrest of dilatation 3. Arrest of descent 4. Failure of descent > 3 hr > 2 hr > 1 hr No descent in deceleration phase or second stage

Second Stage of Labor begin when cervical dilatation is complete and ends with fetal expulsion median duration : in nulliparas - 50 min, in multiparas - 20 min average second stage labor was lengthened about 25 minutes by regional analgesia limit of the length of the second stage in nulliparas : 2 hrs & extended to 3 hrs when regional analgesia in multiparas : 1 hr & extended to 2 hrs with regional analgesia The relationship between the duration of second stage labor and pregnancy outcome maternal effects : postpartum hemorrhage & infection increased but incidence is quite small infant effects They concluded that there is no compelling reason to intervene with a possibly difficult forceps or vacuum extraction but after 3 hours in the second stage, delivery by cesarean or other operative method increased

1st & 2nd stage of normal labor

Inadequate labor Uterine dysfunction Fetopelvic disproportion Ruptured membranes without labor

Uterine Dysfunction Characterized by lack of progress In the latent phase, the diagnosis is difficult One of the most common errors is to treat women for uterine dysfunction who are not yet in active labor There have been three significant advances in the treatment of uterine dysfunction: improvement of perinatal morbidity and mortality dilute intravenous infusion of oxytocin more frequent use of cesarean delivery rather than difficult midforceps delivery

Uterine Dysfunction The lower limit of contraction pressure required to dilate the cervix is 15 mmHg (Caldeyro-Barcia, 1950) Normal spontaneous contractions often exert pressures of about 60 mmHg (Hendricks,1959) Two types of uterine dysfunctions hypotonic uterine dysfunction hypertonic uterine dysfunction or incoordinate uterine dysfunction

Types of uterine dysfunction Hypotonic uterine dysfunction There is no basal hypertonus Uterine contractions have a normal gradient pattern (synchronous) The slight rise in pressure during a contraction is insufficient to dilate the cervix. Hypertonic uterine dysfunction Basal tone is elevated appreciably the pressure gradient is distorted perhaps by contraction of the midsegment of the uterus with more force than the fundus by complete asynchronism of the impulses originating in each cornu a combination of these two

Reported causes of uterine dysfunction Epidural analgesia Lengthening of both first- and second-stage labor as well as slowing of the rate of fetal descent Chorioamnionitis Maternal intrapartum infection plays a role in the development of abnormal uterine activity Maternal position during labor Walking during labor have been reported to shorten labors, decrease the need for augmentation with oxytocin, decrease the need for analgesia, and lower the frequency of instrumental vaginal delivery Contraction frequency & intensity have been reported to increase with sitting or standing (Miller 1983) Uterine contractions occur more frequently but with less intensity in the supine position compared with lying on her side. There is no conclusive evidence that upright maternal posture or ambulation improves labor (Lupe and Gross 1986)

Reported causes of uterine dysfunction Birthing position in second-stage labor Russell(1969) described a 20 to 30 percent increase in the area of the pelvic outlet with squatting compared with the supine position Crowley (1991) compared to deliver in an obstetrical birth chair with to deliver in bed : there were no advantages with use of the birthing chair, but hemorrhage was increased in the group. De jong(1997) found no increase in hemorrhage with the sitting position The benefits of the upright position : less maternal pain and enhanced maternal satisfaction with the birthing experience Immersion in water Advocated as a means of relaxation (Odent, 1983) Not alter the rate the rate of cervical dilatation, length of labor, route of delivery, or analgesia use (Schorn, 1993)

Fetopelvic disproportion This arises from either diminished pelvic size, excessive fetal size, or more usually, a combination of both. Pelvic capacity Any contraction of the pelvic diameters that diminishes the capacity of the pelvis can create dystocia Contractions of the pelvic inlet, the midpelvis, the pelvic outlet and combinations of these.

Fetopelvic disproportion Contracted Pelvic Inlet  Definition AP diameter  < 10 cm or transverse diameter  < 12 cm Diagonal conjugate < 11.5 cm Both AP diameter (< 10cm) and transverse diameter (< 12cm) are contracted -> dystocia is much greater Cervical dilatation is facilitated by hydrostatic action of the unruptured membranes or, after their rupture, by direct application of the presenting part against the cervix. In contracted pelvis, however, when the head is arrested in the pelvic inlet, the entire force exerted by the uterus acts directly upon the portion of membranes that overlie the dilating cervix. Consequently, early spontaneous rupture of the membranes is more likely to result.  Fetal presentation and position face and shoulder presentation ( x3) & cord prolapse ( x4-6)

Three anteroposterior diameters of the pelvic inlet

Fetopelvic disproportion Average midpelvis measurements Transverse (interspinous) 10.5cm Anteroposterior (from the lower border of the symphysis pubis to the junction of the fourth and fifth sacral vertebrae) 11.5cm Posterior sagittal (from the midpoint of the interspinous line to the same point on the sacrum) 5cm Contracted Midpelvis Definition The interischial spinous diameter + posterior sagittal diameter  < 13.5 cm The interischial spinous diameter < 8 cm Suggestive findings The ischial spines are prominent The pelvic side walls converge The sacrosciatic notch is narrow

Transverse diameter of the midpelvis

Fetopelvic disproportion Contracted Pelvic Outlet Definition The interischial tuberous diameter < 8 cm Outlet contraction without concomitant midplane contraction is rare. Prognosis Diminution in the intertuberous diameter with consequent narrowing of the anterior triangle must inevitably force the fetal head posteriorly. Depend on the size of the posterior triangle on the interischial tuberous diameter& posterior sagittal diameter of outlet Production of perineal tears

Fetopelvic disproportion

Pelvic fractures and rare pelvic contraction Trauma from automobile collisions: most common cause of pelvic fractures Bilateral fractures of the pubic rami :compromise of birth canal capacity by callus formation or malunion Careful review of previous of previous x-ray and possibly computed tomographic pelvimetry later in pregnancy, unless c/sec is performed for another reason. Rare pelvic contraction : dwarfs, poliomyelitis, kyphoscoliosis

Estimation of pelvic capacity Clinical estimation Narrow pelvic arch (<90 degrees) : narrow pelvis Unengaged fetal head -> excessive fetal head size or reduced pelvic inlet capacity X-ray pelvimetry 5 factors that determines successful vaginal deliveries. size and shape of the bony pelvis size of fetal head force of uterine contractions moldability of the fetal head presentation and position of the fetus Indications for X-ray pelvimetry for trial of vaginal delivery in case of breech presentation and previous injury or disease likely to affect bony pelvis

Estimation of pelvic capacity Computed tomographic scanning Advantages Reduction in radiation exposure Greater accuracy Easier to perform Comparable cost Magnetic resonance imaging Lack of ionizing radiation Accurate pelvic measurements Complete fetal imaging Providing the potential for evaluating reasons for soft tissue dystocia

Excessive fetal size Although the fetal weight threshold decreased from 5000g to 4500g, has been that fetal size seldom is a suitable explanation for failed labor. The greatest obstetrical concern was not that the fetal head might fail to traverse the pelvic passage, but, rather that the shoulders might not fit through the pelvic inlet or outlet. Selection of a fetal size threshold to predict fetopelvic disproportion and prevent obstructed labor, is not possible because most cases of disproportion occur in fetuses whose weight is well within the range of the general obstetric population. Two thirds of infants requiring c/sec at Parkland Hospital after an attempt at forceps delivery failed, weighed less than 3700g Thus, fetopelvic disproportion usually is not associated with excessive fetal size.

Estimation of fetal head size Clinical estimation - Muller method In an occiput presentation, the brow and the suboccipital region are grasped through the abdominal wall with the fingers and firm pressure is directed downward in the axis of the inlet. Fundal pressure by an assistant usually is helpful. The effect of the forces on the descent of the head can be evaluated by concomitant vaginal examination. No disproportion -> the head readily enters the pelvis, and vaginal delivery can be predicted. Inability to push the head into the pelvis does net necessarily indicate that vaginal delivery is impossible. Flexed fetal head that overrides the symphysis pubis -> presumptive evidence of disproportion No relation between dystocia and failure of descent of the head

Ruptured membranes without labor Membrane rupture without spontaneous uterine contractions occurs in about 8 % of terms Management stimulation of contractions when labor did not begin after 6 to 12 hours because of amnionitis Almost 75 % of those observed entered labor spontaneously within 24 hours The cesarean delivery rate was almost tripled in women undergoing labor induction ( Duff 1984 ) In contrast, there was no advantage to delaying intervention because of neonatal infections ( Wagner 1989 ) Prostaglandin E2 to reduce the admission-to-delivery interval in non-laboring women after membrane rupture at term (Chua 1995, Mahood and Dick 1995) Labor induction with intravenous oxytocin was the preferred management (Hannah 1996)

Diagnosis of inadequate labor Active-phase disorders : neither failure to progress nor cephalopelvic disproportion are precise terms (ACOG, 1995) A more practical classification is to divide labor abnormal into either slower-than-normal (protraction disorder) or complete cessation of progress (arrest disorder). The woman must be the active phase of labor (cervix dilated 3 to 4 cm or more) to diagnose either these. Active-phase arrest( no dilatation for 2 hours or more) in 5 percent of term nulliparas. Inadequate uterine contractions, defined as less than 180 Montevideo units were diagnosed in 80 percent of women with active-phase arrest. A labor management in which protraction is defined as less than 1cm/hr cervical dilatation for a minimum of 4 hours. (WHO,1994)

Diagnosis of Active Phase Labor Disorders To effectively induce or augment labor with oxytocin, 90 percent of women achieve 200 to 225 Montevideo units, and 40 percent achieve at least 300 Montevideo units. Before the diagnosis of arrest during first stage labor is made, both of these criteria should be met : The latent phase has been completed, with the cervix dilated 4cm or more. A uterine contraction pattern of 200 Montevideo units or more in a 10-minute period has been present for 2 hours without cervical change 2-hour rule on the grounds that a longer time, i.e., at least 4 hours, is necessary before concluding that the active phase of laber has failed.

Fetal station at onset of active labor Both protraction and arrest labor disorders in women with fetal head stations above +1cm & that the higher the station at the onset of labor in nulliparas, the more prolonged the labor. (Friedman and Sachtleben , 1965) The fetal station at the time of arrested labor was also a risk factor for dystocia. The prognosis for dystocia ,however, was not related to incremen- tally higher fetal head stations above the pelvic midplane (0 station) 86 percent of nulliparous women without fetal head engagement at diagnosis of active labor delivered vaginally. Thus, lack of engagement at the onset of labor, although a statistical risk factor for dystocia, should not be assumed to necessarily predict fetopelvic disproportion

Second-stage disorder With achievement of full cervical dilatation, the great majority of women cannot resist the urge to “ bear down” or “push” each time the uterus contract Coaching women to push forcefully, compared with letting them follow their own urge to bear down, has been reported to offer no advantage (Parnell , 1993)

Cause of inadequate expulsive forces Heavy sedation or conduction analgesia-lumbar epidural, caudal, or intrathecal-are likely to reduce the reflex urge to push, and at the same time may impair ability to contract the abdominal muscles sufficiently. Careful selection of the kind analgesia & timing of its administration are important to avoid comprise of voluntary expulsive efforts. Continuous epidural analgesia -> the paralytic efforts to wear off so that the woman can generate intra-abdominal pressure sufficient to move the fetal head into position appropriate for outlet forceps delivery. For the woman who cannot bear down appropriately with each contraction because of great discomfort, analgesia is likely to be of considerable benefit

Maternal-fetal effects of dystocia Maternal effects Intrapartum infection Uterine rupture Pathological retraction ring Fistula formation due to pressure necrosis Pelvic floor injury

Differentiation of Uterine Activity During active labor, uterus differentiates into 2 distinct parts        Upper segment actively contracting , becomes thicker as labor advances quite firm or hard on abdominal palpation1  Lower segment relatively passive develops into a much thinly walled passage for the fetus much less firm on abdominal palpation     Physiologic retraction ring : As labor progresses -> thinning of the lower uterine seg- ment and the concomitant thickening of upper segment -> the boundary between the two is marked by a ridge on inner uterine surface  Pathologic retraction ring (the ring of Bandle) In obstructed labor -> lower uterine segment’s extreme thinning -> the ring is very prominent

Pathological retraction ring

Maternal-fetal effects of dystocia Prolonged membrane rupture & intrauterine infection Caput succedaneum The caput may reach almost to the pelvic floor while the head is not engaged. Fetal head molding Tentorial tears, laceration of fetal blood vessels and fetal intracranial hemorrhage

Labor Management Protocols Active management of labor (O'Driscoll 1984) : amniotomy and oxytocin Labor is diagnosed : painful uterine contractions + complete cervical dilatation, bloody show, or ruptured membranes Pelvic examination : Performed each hour for the next 3 hours -> at 2 hour intervals When dilatation has not increased by at least 1 cm ->amniotomy Progress is again assessed at 2 hours, If not significant progress (i.e., 1 cm/hr) -> high-dose oxytocin infusion

Parkland Hospital Labor Management Protocol Pelvic examinations be performed approximately every 2 hours When the cervix does not dilate within about 2 hours of admission -> amniotomy In women whose labors do not progress -> an intrauterine pressure catherter Hypotonic contractions and no cervical progress -> high-dose oxytocin regimen Cesarean rates in nulliparous and parous women were 8.7 and 1.5 %, respectively These labor interventions and the relatively infrequent use of cesarean delivery did not jeopardize the fetus-newborn infant

Labor management protocols at Parkland Hospital

Precipitate labor and delivery Definition Expulsion of the fetus in less than 3 hours Causes An abnormally low resistance of the soft parts of the birth canal Abnormally strong uterine and abdominal contractions The absence of painful sensations

Precipitate labor and delivery Maternal effects Uterine rupture Extensive lacerations of the cervix, vagina, vulva, or perineum Amnionic fluid embolism Postpartum hemorrhage from uterine atony

Precipitate labor and delivery Effects on fetus and neonate Increased perinatal mortality and morbidity Intracranial trauma Erb-Duchenne palsy The infant may fall to the floor and be injured. Resuscitation is not immediately available.

Precipitate labor and delivery Treatment The use of tocolytic agents such as magnesium sulfate is unproven in these circumstances. Use of general anesthesia with agents that impair uterine contractibility is often excessively heroic. Certainly, any oxytocin agents being administered should be stopped immediately.