Induction of Labor

Induction of labor can be

• Medically indicated (eg, for preeclampsia or fetal compromise)

• Elective (to control when delivery occurs)

Before elective induction, gestational age must be determined. Commonly, elective induction has been avoided at 39 weeks because of lack of evidence for perinatal benefit and concern about a higher frequency of cesarean deliveries and other adverse outcomes. This practice may be changing, partly because a 2018 study showed that induction of low-risk women at 39 weeks reduced the frequency of cesarean deliveries (but not perinatal adverse outcomes) compared with expectant management (1).

Contraindications to induction include having or having had the following:

• Transfundal uterine incision (eg, for a cesarean delivery or myomectomy)

• Myomectomy involving entry into the uterine cavity

• Prior classical (vertical) cesarean incision in the thickened, muscular portion of the uterus

• Open maternal-fetal surgery (eg, myelomeningocele closure)

• Active genital herpes

• Placenta previa or vasa previa

• Abnormal fetal presentation (eg, transverse lie, umbilical cord presentation, certain types of fetopelvic disproportion)

Multiple prior uterine scars and breech presentation are relative contraindications.

If the cervix is closed, long, and firm (unfavorable), the goal is to cause the cervix to open and become effaced (favorable). Various pharmacologic or mechanical methods can be used. They include

• Misoprostol 25 mcg vaginally every 2 to 4 hours or 25 to 50 mcg orally every 2 hours

• Prostaglandin E2 given intracervically (0.5 mg) or as an intravaginal pessary (10 mg [prostaglandins are contraindicated in women with prior cesarean delivery or uterine surgery because these drugs increase the risk of uterine rupture])

• Oxytocin in low or high doses

• Use of laminaria and transcervical balloon catheters, which may be useful when other methods are ineffective or contraindications exist

• Mechanical dilation with a Foley (ie, double-lumen latex) catheter plus misoprostol or oxytocin (1)

Once the cervix is favorable, labor is induced.

Constant IV infusion of oxytocin is the most commonly used method; it is safe and cost-effective. Low-dose oxytocin is given at 0.5 to 2 milliunits/minute, increased by 1 to 2 milliunits/minute, usually every 15 to 60 minutes. High-dose oxytocin is given at 6 milliunits/minute, increased by 1 to 6 milliunits/minute every 15 to 40 minutes to a maximum of 40 milliunits/minute. With doses>40 milliunits/minute, excessive water retention may lead to water intoxication. Use of oxytocin must be supervised to prevent uterine tachysystole (> 5 contractions in 10 minutes averaged over 30 minutes), which may compromise the fetus.

External fetal monitoring is routine; after amniotomy (deliberate rupture of the membranes), internal monitoring may be indicated if fetal status cannot be assessed externally. Amniotomy can be done to augment labor when the fetal head is applied to a favorable cervix and not ballotable (not floating).