• Nathan Riley, MD

Obgyno Wino Podcast Episode 68 - Induction of Labor

“There is nothing absolute and final. If everything were ironclad, all the rules absolute and everything structured so no paradox or irony existed, you couldn't move. One could say that man sneaks through the crack where paradox exists." - Itzhak Bentov

Brut from Jaume Serra Cristalino

PB#107 - Published August 2009 (Reaffirmed 2019)

Five Pearls

1. Especially if it's her first baby, "ripening" the cervix is important before you try to generate regular contractions

2. A Bishop score 8 when you start oxytocin infusion carries an equal likelihood of vaginal delivery as you would see in spontaneous labor

3. Labor progression is often much slower for women undergoing IOL, so allow for a full 12-18 hrs of latent labor before diagnosis failed induction

4. Membrane stripping can be VERY uncomfortable. Please explicitly consent your patient before attempting this.

5. The ARRIVE trial is regularly misinterpreted as evidence that IOL at 39 wga is actually safer for mom and baby than expectant management.

When is labor induction indicated? (no absolutes here!)

- placental abruption

- chorioamnionitis

- fetal demise

- gestational HTN

- preeclampsia, eclampsia

- postterm pregnancy

- maternal medical conditions like DM, renal disease, COPD, chronic HTN, APS

- severe fetal growth restriction, isoimmunization, oligohydramnios

- logistical reasons (but only if you're SURE that the fetus is at least 39 wga: ultrasound confirmation of GA at <20 wks, 30 weeks of heart tone auscultation, or 36 wks or more since positive pregnancy test)

- mature fetal lung test should be obtained if any doubt about GA

**Two cents: using the ARRIVE trial as a means to justify earlier induction is lazy. Stop it. (Evidence-based birth did a nice review of this)

Contraindications to IOL

- vasa previa or complete placenta previa

- transverse fetal lie or breech presentation

- cord prolapse

- history of prior classical c-cesarean delivery

- active genital herpes lesions

- history of prior myomectomy in which the endometrial cavity was entered

What are my options?

- synthetic oxytocin (Pitocin) infusion, prostaglandin analogues (vaginal or buccal), membrane stripping, amniotomy, mechanical and osmotic dilators, and nipple stimulation

Cervical ripening is generally the first step

- especially if it's her first baby, "ripening" the cervix is important before you try to generate regular contractions

- ripening softens, thins, and dilates the cervix

- ripening also happens naturally as a result of the baby's head (or rump) bumping against the cervix before labor ensues (this is often the spark that ignites labor because the ripening process also stimulates the release of endogenous oxytocin from the pituitary!)

- this softening occurs as the result of collagen breakdown and remodeling, changes in glycosaminoglycans, and inflammation

- once the cervix has ripened and dilated to a Bishop score of ≥8, then the goal becomes to generate regular, strong contractions (waiting until Bishop score is 8 or more carries an equal likelihood of vaginal delivery as you would see in spontaneous labor)

**It's important to note that pharmacological ripening agents don't reduce the risk of c-section

Methods for ripening

- synthetic prostaglandins: prostaglandin E1 analogue (PGE1; misoprostol) and E2 analogue (PGE2; dinoprostone and cervidil)

- mechanical dilation: intracervical Foley or cervical ripening balloon (CRB)

- osmotic dilators: Laminaria japonicum (associated with higher risk of peripartum infections)

- extramniotic saline infusion

Misoprostol is the favorite prostaglandin in the U.S.

- adminstration options: vaginal, oral, sublingual, or buccal

- no evidence that misoprostol (or dinoprostone) has any long term consequence for mom or baby in the absence of fetal distress (e.g. uterine tachysystole caused by the agents)

- FDA approved for this use but doses and dose intervals not specified with regards to safety

- the majority of adverse effects were found in association with doses >25 mcg

- contraindicated if history of prior c-section (increased risk of uterine rupture)

- start with 25 mcg, then repeat dose in 3-4 hrs (OK to increase to 50 mcg but wait at least 6 hrs between doses)

- dinoprostone can be repeated 6-12 hrs (max dose of 1.5 mg over the course of IOL)

- wait until 4 hrs after last PGE1 administration before starting oxytocin

- wait 6 hrs after dinoprostone gel or 60 minutes after dinoprosteon slow-release tablet ("soap on a rope")

- hold off on repeating doses if uterus is contracting up a storm

- per the publication of this PB, buccal or sublingual misoprostol hasn't been well-studied, but there is definitely data out there (spoiler: vaginal wins, but oral is less likely to cause tachysystole)

Dinoprostone deets

- two forms: gel-filled syringe containing 0.5 mg or a vaginal insert contain 10 mg (slow-release compared to gel)

- manufacturer cautions about use in patients with asthma, severe hepatic or renal dysfunction, or glaucoma (unlikely to be a real issue, though; in fact, PGE2 is a bronchodilator)

- can cause low grade fever

Oxytocin for cervical ripening

- normally, we think of synthetic parenteral oxytocin infusion (i.e. Pitocin) as a means to generate strong, regular uterine contractions

- at low dose infusion rates, it can also facilitate cervical ripening

- kicks in around 3-5 minutes after starting the infusion; steady state reached by 40 minutes

- uterine receptors plateau by around 34 wga (meaning a weaker response at earlier GA)

Membrane stripping

- provider will use their hands to encircle the inside of the cervix in order to stimulate the release of endogenous phospholipase A2 and prostaglandin F2α

- increases likelihood of spontaneous labor within 48 hrs and reduce the need for other induction methods

- expect vaginal spotting

- no evidence that is increases risk of PROM

- insufficient guidance to guide counseling if patient is known to be GBS carrier

Note: membrane stripping can be VERY uncomfortable. Please please please explicitly consent your patient before attempting this!


- artificial rupture of membranes (AROM) could, in theory, get labor going

- no evidence that it works that well as it often leads to unpredictably long intervals until the onset of contractions

- efficacy may be improved if combined with low dose oxytocin infusion

- insufficient safety data to guide counseling is patient is known GBS carrier

- risk of cord prolapse, rapid descent (+/- tracing changes), chorioamnionitis, cord compression, rupture of vasa previa

Nipple stimulation

- pretty self-explanatory: massaging the breasts and/or nipples

- on that note, anything that makes you feel connected to your partner can also stimulate labor: make out sessions, intercourse, masturbation, or even playing with a puppy! (not evidence-based apart from anecdotally)

- the method has only been studied in low-risk populations, but Cochrane did not find an increased risk for uterine tachysystole, mec-stained fluid, or c-section on systematic review (in fact, it HAS been shown to decrease risk for postpartum hemorrhage!)

**Of note, the same review also found an increased trend in perinatal death in women who utilized nipple stimulation.

Which ripening method is better?

- little evidence comparing mechanical methods to prostaglandins

- intracervical Foley is cheaper than prostaglandins (but the CRB is more expensive)

- prostaglandins require special handling (e.g. dinoprostone must be kept refrigerated --> they are activated at body temp!) and carry higher risk of uterine tachysystole than Foley

- in patients with an unfavorable cervix, one study found that placement of intracervical Foley balloon prior to beginning oxytocin decreases the duration of labor and decreased the risk of c-section

- studies comparing intracervical Foley to dinoprostone have shown no difference in these outcomes

- the addition of parenteral oxytocin infusion to intracervical Foley (concurrently) has not been shown to shorten labor

- extraamniotic saline infusion compared to parenteral oxytocin infusion has no added benefit

- misoprostol (PGE1) has performed better than parenteral oxytocin or dinoprostone (PGE2) in several studies (shorter labor, less need for epidural BUT higher risk for uterine tachysystole)

Don't set up your patient for failure

- available data suggests that for nulliparous patients undergoing IOL with an unfavorable cervix (Bishop score <6), there is a 2x increased risk for c-section

- labor progression is often much slower for women undergoing IOL, so allow for a full 12-18 hrs of latent labor before diagnosis failed induction

- our tendency to diagnosis "failed induction of labor" is a primary reason for the super high primary c-section rate in our country (~25%)

- ripen the cervix to Bishop score of 8 or better before starting oxytocin infusion!!

- use mechanical and medical cervical ripening agents if need-be


How should a patient be monitored during IOL?

- intermittent monitoring is probably fine (20 minute strip every hour in latent phase), though it's generally recommended to monitor FHR for 30-60 min after the administration of prostaglandins as this is the most likely time frame for the development of uterine tachysystole (if a patient is on oxytocin, continuous monitoring is recommended)

- high risk patient should be continuously monitored

What happens if you detect uterine tachysystole?

- The art of labor induction lies in providing just enough push to get labor going without causing fetal distress

- "normal" contraction pattern: ≤5 contractions in a 10-minute over 30-minutes of observation

- tachysystole: >5 contractions in a 10-minute over 30-minutes of observation

- when you use the word tachysystole, you must ALWAYS further qualify them as to the presence or absence of associated FHR decelerations

- the presence of tachysystole WITHOUT tracing issues isn't necessarily an issue (though you could remove a sustained-release dinoprostone "soap on a rope" if the uterus begins contracting up a storm

- lower risk of tachysystole with lower doses of misoprostol (25 mcg versus 50 mcg) and with longer intervals between doses (6 hrs versus 3 hrs)

- if PGE2 tablet is in the vagina, pull it out; if oxytocin is infusing, stop it

- if tachysystole is accompanied by cat 3 tracing (1) sinusoidal pattern OR, 2) absent variability + recurrent variable or late decels or bradycardia, urgent c-section may be warranted (try conservative measures to improve the tracing first! --> hydration, correction of maternal blood sugars, maternal repositioning, etc.)

Can induction begin in the outpatient setting?

- insufficient data to guide prostaglandin use

- Foley bulbs or CRBs are safe in the outpatient setting

Which induction methods are OK in prelabor rupture of membranes (PROM)

- intravaginal prostaglandins have not been shown to increase risk of infection

- the PB claims that the use of intracervical Foley or CRB hasn't been studied in PROM, but it definitely has, and data (also this one along with this lovely prospective trial comparing FB to prostaglandins) suggests that it's totally safe (i.e. no increased risk of chorio)

- For more information on management of prelabor rupture of membranes...go to my show notes (PB#188)


- most of the data has been extrapolated from experience with managing 2nd trimester miscarriage

- in 2nd trimester, dilation and evacuation (D&E) is appropriate

- if provider trained in D&E is not available or if patient not willing, then IOL is also an option

- misoprostol is safe as early as 24 wga; at <28 wga, vaginal misoprostol is the most effective method of IOL for this purpose regardless of Bishop score

- higher doses of misoprostol are reasonable given we aren't concerned with uterine tachysystole: 200-400 mcg q4hr

- misoprostol is also OK even if history of prior c-section at <28 wga

- oxytocin and intracervical ripening balloons/Foley are also OK

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