Induction of Labor

Induction of labor

1) membrane rupture without spontaneous onset of labor
2) maternal hypertension
3) nonreassuring fetal status
4) postterm gestation

1) uterine contraindications: prior distruption such as a classical incision or uterine surgery, placenta previa
2) fetal contraindications: appreciable macrosomia, some fetal anomalies such as hydrocephalus, malpresentations, or nonreassuring fetal status
3) maternal contraindications: maternal size, pelvic anatomy, and selected medical conditions such as active genital herpes

-preinduction cervical ripening
*Bishop score: dilatation, effacement, station, consistence, and position of the cervix
successful: score of 9 or greater
1. pharmacological techniques
1) prostaglandin E2 (dinoprostone)
: histological changes; dissolution of collagen bundles
increase in submucosal water content
: use of low-dose; increases the chances of successful induction
decreases the incidence of prolonged labor
reduces total and maximal oxytocin doses
: administration
① remains recumbent for at least 30 minutes following application
② from 30 minutes to 2 hours: prudent observation period
-no change in uterine activity or fetal heart rate
? transferred or discharged
-contractions occur ? usually apparent in the first hour
? show peak activity in the first 4 hours
if regular contractions persist? FHR monitoring, V/S record
* oxytocin induction: delayed for 6 to 12 hours
: side effects
-uterine hyperstimulation (1% for intracervical gel, 5% for intravaginal gel)
-fever, vomiting, diarrhea ? negligible
-caution: pts with glaucoma, severe hepatic or renal impairment, or asthma
2) prostaglandin E1 (misoprostol; Cytotec)
: inexpensive
: stable at room temperature and easily administered orally or placed into the vagina, but not the cervix
: vaginal misoprostol
-25 ug dose;
decrease the need for oxytocin
achieve higher rates of vaginal delivery within 24 hrs of induction
significantly reduce induction-to-delivery intervals
-50 ug dose;
increased tachysystole, meconium passage, and meconium aspiration
increased incidence of cesarean delivery due to uterine hyperstimulation
: oral misoprostol
-oral and vaginal applications were of similar efficacy but that an oral dosage of 200 ug was associated with more frequent abnormal uterine contractility
-100 ug oral dose was as effective as the 25 ug intravaginal dose
2. mechanical techniques
: extra-amnionic saline infusion after Foley catheter placement and inflated 30mL-balloon
2) hygroscopic cervical dilators
: low cost, ease of placement, and their ability to be quickly removed
3) membrane stripping
: safe and associated with a decreased incidence of postterm gestation
: significantly increased levels of plasma prostaglandins with membrane stripping

-Labor induction with oxytocin
1. Techniques for intravenous oxytocin
* Goal: effect uterine activity that is sufficient to produce cervical change and fetal descent while avoiding uterine hyperstimulation and/or development of a nonreassuring fetal status
: Contractions persist as greater than 5 in a 10-minute period or 7 in a 15-minute period ? contractions evaluated continually and oxytocin discontinued
: oxytocin dosage
Regimen Starting dose
(mU/min) Incremental increase
(mU/min) Dosage interval
(min) Maximal dose
Low-dose 0.5-1
1-2 1
2 30-40
15 20
High-dose 6 6,3,1 15-40 42

: Risks versus Benefits
1) uterine rupture: uncommon today
2) water intoxication: oxytocin has amino-acid homology similar to arginine vasopressin ? antidiuretic action ? convusions, coma, and even death
: Uterine contraction pressures with oxytocin stimulation
-arrest of first stage labor: the uterine contraction pattern should exceed 200 Montevideo units for 2 hours without cervical change
2. Amniotomy
1) Elective amniotomy
: artificial membrane rupture with the intention of accelerating labor
: amniotomy at about 5 cm dilatation accelerated spontaneous labor 1 to 2 hours
2) Amniotomy induction
: amniotomy alone or combined with oxytocin was superior to oxytocin alone
: early amniotomy was increased incidence of chorioamnionitis(23%) and cord compression monitoring patterns(12%)