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Ch.20 Induction and Augmentation of labor

부산백병원 산부인과R2 서영진

Common indications for induction :membrane rupture without spontaneous onset of labor maternal hypertension nonreassuring fetal status postterm pregnancy

GENERAL CONCEPTS Elective induction :not recommended -increase c/sec (especially, nulliparas)

:when benefits -mother or fetus > continuing the pregnancy

:emergent indication -ruptured membranes with chorioamnionitis severe preeclampsia

GENERAL CONCEPTS

:relative indication -at term with history of rapid labor reside an appreciable distance from hospital (mountain, winter)

:complication -increase chorioamnionitis and c/sec c/sec: poorly prepared for labor (ex. unripe cervix or a myometrium unable to achieve effective synchronous contraction)

CONTRAINDICATIONS Uterine contraindications :prior disruption (classical incision or uterine surgery) placenta previa Fetal contraindication :macrosomia fetal anomaly- hydrocephalus, malpresentation nonreassuring fetal status

Maternal contraindication :maternal size, pelvic anatomy ,medical condition (ex.genital herpes)

PREINDUCTION CERVICAL RIPENING Important factor of labor induction :the condition or favorability of the cervix :physical characteristics of the cervix and lower seg. :presenting part, station

Quantifiable method ‘BISHOP SCORE’ :if score > 9, usually successful :IV oxytocin stimulation

PREINDUCTION CERVICAL RIPENING Phamacological techniques :Prestaglandin E2 (PGE2) -local application of PGE2 gel (dinoprostone) -Cx ripening -dissolution of collagen bundle increase submucosal water content -low-dose PGE2 (1988) increase successful induction decrease prolonged labor reduce total and maximal oxytocin dose

PREINDUCTION CERVICAL RIPENING -PGE2 gel (Prepidil): 2.5-mL sylinge contains dinoprostone(0.5mg) less uterine activity greater efficacy in women with very unripe Cx -Crevidil(10-mg dinoprostone vaginal insert) slower release than gel shorten the interval from induction-to-delivery can be removed (when hyperstimulation occur)

:Patient selection -Bishop score < 4

PREINDUCTION CERVICAL RIPENING :Administration -continuous Ut activity & FHR monitoring -remain recumbent for at least 30 min -observation 30 min~2hrs -contraction occur in the first hour and show peak in the first 4 hrs FHR and V/S recording -minimum safe time interval (PGE2oxytocin) ;not be established usually, 6 to 12 hrs

PREINDUCTION CERVICAL RIPENING :Side effect -Ut hyperstimulation (>6 contraction in 10 min for a total of 20 min) begins within 1 hr remove irrigation of Cx, vagina: not be helpful

-systemic effect nausea, vomiting, diarrhea glaucoma, hepatic and renal ds, asthma

PREINDUCTION CERVICAL RIPENING

: Prostaglandin E1 (PGE1) -Misoprostol (Cytotec) ` available as a 100 ㎍ tablet for prevention of ulcer ` preinduction cervical ripening and labor induction → inexpensive stable at room temperature easily administered olrally placed into the vagina but not cervix ` ACOG (1999) → intravaginal 25 ㎍ every 3 to 6 hr

: vaginal misoprostol -misoprostol PV > intracervical PGE2 gel -ACOG (1999) `recommend 25 ㎍ dose PV →decrease the need for oxytocin higher rates of vaginal delivery within 24hrs reduce induction-to-delivery intervals →caution : hyperstimulation with fetal heart rate change

` if 50 ㎍ dose, -tachysystole, meconium passage & aspiration increased c/sec rate (hyperstimulation)

: prior uterine surgery – risk of uterine rupture → not use Misoprostol

: oral Misoprostol - Windrim(1997) orally administration = intavaginal (cervical ripening,labor induction) - Bennett(1998) but more frequent FHR abnormal - Adair(1998) 200 ㎍ oral; more frequent abnormal Ut contractility - Wing (1999) 50 ㎍ oral < 25 ㎍ vagina (cervical ripening,labor induction) 100 ㎍ oral = 25 ㎍ intravagina

Mechanical techniques : EASI (extra-amnionic saline infusion) -foley catheter with 30cc ballooning -rapid improvement in Bishop score shorter labor -c/sec rate 4~46% : variable report -Schreyer (1989) Bishop score ( > vag PGE2) -Vengalil (1998) c/sec, del time ( = vag PGE1 q 4hr) -Hemlin & Moller (1998) Cx ripening ( > intraCx PGE2)

: Guinn (2000) -intracervical PGE2 laminaria + IV oxytocin EASI + oxytocin →c/sec rate : similar del time : 24.8 hrs vs 21.5 hrs vs 18hrs

Hygroscopic cervical dilators : rapid improvement of cervical status : no beneficial effect on c/sec rate or delivery

interval : low cost, ease of placement, quickly removed : longer interval-to-delivery time (compare with

EASI) : some benefit for initiation for cervical dilation

Membrane stripping : performed by inserting the index finger as far through the internal os as possible and rotating twice through 360 degrees to separate the membranes from the lower segment : safe and decreased incidence of postterm gestation : not increase-membrane rupture, infection, bleeding : increased plasma prostaglandins : benefit- < 48hrs, < 1 week , < 41 weeks

LABOR INDUCTION AND AUGMENTATION WITH OXYTOCIN Oxytocin : first polypeptide hormone synthesized : following delivery to induce or augment labor Induction : stimulation of contraction before the spontaneous onset of labor, with or without ruptured membranes Augmentation : stimulation of spontaneous contractions that are considered inadequate because of failure of progressive dilatation and descent

- oxytocin IV infusion to augment inadequate labor due to uterine dysfunction exclude fetopelvic disproportion - fetal heart rate and contraction pattern be obsreved closely

Technique for administration of intravenous oxytocin : variety of methods : the goal → produce cervical change fetal descent : avoiding hyperstimulation and nonreassuring (hyperstimulation: >5 in 10 mins or >7 in 15 mins ) ( >60~90 seconds ) : if hyperstimulation oxytocin stop!!! -rapidly decreases the frequency of contractions concentration in plasma rapidly falls half-life is approximately 5 minutes

: uterine response- whthin 3~5 mins steady state- 40 mins →depends on preexisting uterine activity sensitivity cervical status : uterine response - GA 20~30 weeks : increase GA 34 ~ at term : unchanged but, sensitivity ↑ : important factors of oxytocin dosage -cervical dilatation, parity, gestational age

: methods – diluted into 1000ml of a balanced salt solution ( lactated Ringer solution) by infusion pump avoid bolus only IV route typically, 10~20 unit in 1000 ml (10,000~20,000mU → 10~20 mU/ml)

: oxytocin is avoided -abnormal fetal presentation uterine overdistention (hydramnios, large fetus, or multiple fetus) high parity ( >6 ) previous uterine scar

-not contraindication → prior cesarean delivery dead fetus unless CPD

Oxytocin dosage :high-dose(4~6mU/min) vs low-dose (0.5~1.5 mU/min) :at Parkland Hospital (satin, 1992) - low-dose → 1mU/min, interval 20 mins high-dose → 6mU/min, interval 20 mins Max 42mU/min if hyperstimulation, reduce 3mU/min this flexible high-dose protocol : delivery time ↓ forceps delivery ↓ chorioamnionatis ↓ neonatal sepsis ↓ but, c/sec ↑ (fetal disteress, 3% → 6%)

Increasing dosage intervals : vary from every 15 to 40 minutes : Satin (1994) – begin 6mu/min, incremental 6mU/min 20 min interval vs. 40 min interval *c/sec for dystocia 8% vs. 12% Ut hyperstimulation 40% vs. 31% : other regimen -Frigoletto & Xenakis (1995) 4mU/min every 15mins Merril & Zlatnik (1999) 4.5mU/min every 30 mins Univ. of Alabama : begin at 2mU every 15 mins (4,8,12,16,20,25,30 mU/min)

Risk versus benefits : uterine rupture- uncommon today rare in parous women, unless scarred

: water intoxication -oxytcin is similar to arginine vasopressin antidiuretic action renal free water clearance decrease adequate water + oxytocin → convulsion, coma death

Uterine contraction pressures with oxytocin stimulation :spontaneous laboring women- 90~390 Montevideo unit vaginal delivery- 140~150 Montevideo units :in the arrest of active-phase labor -decide the safe upper range of uterine activity (effective and safe protocol for labor augmentation) 200~225 Montevideo unit :ACOG(1995) -arrest of first-stage labor : no cervix change exceed 200 M. unit for 2hrs

Duration of oxytocin administration : when arrest in first-stage labor - usually 2-hr limits - using 4-hr limit, c/sec rate: 1.3%↓ 1/3: vaginal delivery - up to 6-hr limit, 92% vagianl delivery → reducing c/sec rate → regarding the efficacy and safety

Amniotomy : artificial rupture of the membrane commonly used to induce or augment labor : amniorrhexis- rupture only amnion, not chorion

: other indication of amniotomy -internal monitoring when fetal jeopardy intrauterine assessment of contractions when labor has been unsatisfactory

: nonintervention group -60% : > 8cm dilatation before membrane rupture -38% : amniotomy due to internal monitoriong labor augmentation : prevent risk of cord prolapse - fundal and suprapubic pressure rupture during a contraction fetal monitoring

Elective amniotomy : 5cm dilatation accelerated spontaneous labor within 1 to 2 hrs without increasing c/sec and need of oxytocin

Amniotomy induction :used to induce labor but, it implies a firm commitment to delivery :disadvantage -the unpredictable and occasionally long interval to the onset of labor

:amniotomy (+ oxytocin) > oxytocin alone early amniotomy (1~2cm) > late amniotomy (5cm) :chorioamnionitis (23%), cord compresson (12%)

Amniotomy for augmentation : when spontaneous labor is abnormally slow dysfunctional labor

: with oxytocin- shortened labor by 44 minutes