Bishop Score Calculator

SUMMARY:

The purpose of induction of labor is to stimulate uterine contractions before onset of spontaneous labor for vaginal delivery.  The rates of induction of labor have significantly increased during the last decades. In 1990, less than 10% of pregnancies underwent induction of labor, vs 30% by 2019.  Currently, induction of labor is one of the most frequently performed obstetric procedures. A recent RCT comparing elective induction of labor at 39 weeks gestation with expectant management in nulliparous people (the ARRIVE trial – see below in ‘Related ObG Topics’), showed no increase in perinatal morbidity and mortality rates with lower rates of cesarean delivery. These results may lead to an increase in induction rates in the near future.

Indications

Indications include but are not limited to the following

• Maternal conditions
  • Antepartum: Abruptio placentae | Chorioamnionitis | Fetal demise | Gestational hypertension | Preeclampsia | Eclampsia | PROM | Postterm pregnancy
  • Pregestational: Diabetes mellitus | Renal disease | Chronic pulmonary disease | Chronic hypertension | Antiphospholipid syndrome
• Fetal compromise
  • Fetal growth restriction | Isoimmunization | Oligohydramnios
• Logistical reasons >39 weeks
  • Risk of rapid labor | Distance to hospital | Psychosocial indications

Note: See summary of guidance on timing of delivery for medical indications below in ‘Related ObG Topics’

Contraindications 

• Similar to contraindications for vaginal delivery
  • Vasa previa or complete placenta previa
  • Transverse fetal lie
  • Umbilical cord prolapse
  • Previous classical cesarean delivery
  • Active genital herpes infection
  • Previous myomectomy entering endometrial cavity

Cervical Preparation

Bishop Score

• A Bishop score of ≤6 is associated with low rate of successful induction with oxytocin alone, and the use of cervical ripening agents are recommended

Cervical Ripening Agents

• Misoprostol (PGE1 analogue) given intravaginally, orally or sublingually
  • Initial dose: 25 mcg every 3 to 6 hours
  • Delay oxytocin 4 hours after last dose
  • Available evidence supports safety and efficacy
  • Higher rates of tachysystole
    • When compared to PGE₂
    • With dosing ≥50 mcg
  • Contraindications: Prior cesarean and/or uterine surgery due to risk for uterine rupture
• Dinoprostone (PGE₂ preparations) given vaginally via gel or insert
  • 0.5 mg in 2.5 ml syringe gel or 10 mg vaginal insert
  • Second dose after 6 to 12 h (maximum dose of 1.5 mg in 24 hours)
  • Delay oxytocin 6 to 12 hours after last application of gel or 30 to 60 min after insert

Note: After prostaglandin use (misoprostol or dinoprostone), patient should remain recumbent for at least 30 minutes | Fetal heart tracing should be monitored continuously for 30 minutes to 2 hours | FHR monitoring should be continued if regular uterine contractions are persistent

• Mechanical dilators
  • Foley catheter ( 30 to 80 ml): Reasonable and effective option for cervical ripening
  • Double balloon device
  • Others dilator options: Hygroscopic dilation | Osmotic dilators (Laminaria japonicum) | Extra amniotic saline infusion

Methods of Induction 

Oxytocin

• Pitocin is synthetic formulation for oxytocin, with both low-dose and high-dose regimens
  • Low-dose regimen: 0.5 to 2 mU with increasing rate of 1 to 2 mU/min every 15 to 40 minutes
  • High-dose regimen: 6 mU with increasing rate of 3 to 6 mU/min every 15 to 40 minutes
• High-dose regimen:
  • Shorter labor | Less chorioamnionitis | Less cesarean
  • More tachysystole with FHR changes
• Myometrium becomes more sensitive to oxytocin increases with advancing gestation
• Management of tachysystole with FHR changes
  • Decrease/discontinue oxytocin
  • Corrective measures: Turn patient on side | Oxygen | Fluids | Terbutaline

Membrane Stripping

• Mechanical technique
  • Insertion of one or two fingers into the cervix | Continuous circular sweeping motion detaches the inferior pole of the membranes from the lower uterine segment
• Reduces rates of formal induction (2.3% vs 3.1%) and increases rates of spontaneous labor (72% vs 60%)
• Positive GBS – insufficient data for recommendation

Amniotomy

• Better when cervix is favorable
• In combination with oxytocin: Reduces interval from induction to delivery by approximately 5 hours
• Risks: Cord prolapse | Chorioamnionitis
• Avoid, if possible: HIV, hepatitis B or hepatitis C
• Positive GBS: No data to suggest increased risk for neonatal disease when appropriate intrapartum antibiotic prophylaxis is given

Nipple Stimulation

• Increase likelihood of labor when cervix is favorable
• Only studied in low-risk populations
• In meta-analysis
  • Decrease in women not in labor after 72 hours
  • Decrease in PPH
  • No impact on meconium-stained amniotic fluid or cesarean delivery
  • Due to association with an increased trend toward association with perinatal death “this practice is not recommended in an unmonitored setting”

Specific Clinical Scenarios 

Ruptured Membranes

• Induction with oxytocin is associated with decreased
  • Interval between PROM and delivery
  • Frequency of chorioamnionitis
  • Postpartum febrile morbidity
• Prostaglandins appear safe and effective

Intrauterine Fetal Demise

ACOG 2020

• <28 weeks
  • Misoprostol 400 to 600 mcg vaginally every 4 to 6 hours
• >28 weeks
  • Standard obstetric protocol for labor induction
• Prior uterine scar
  • <28 weeks: Lower doses of Misoprostol (200 mcg) may be preferred
  • >28 weeks: Foley for cervical ripening
• Prior classical incision
  • Limited data to guide clinical practice

SFP 2013

• <28 weeks
  • Misoprostol-only: 100 to 200 mcg vaginally every 4 hours
  • Misprostol-mifepristone regimen: Mifepristone 200 mcg or 600 mcg, followed by misoprotol 36 to 48 hours later | Misoprostol 200 mcg or 400 mcg every 4 hours
  • Addition of mifepristone may shorten the time to expulsion
• Prior uterine scar
  • Consider using 200 mcg or less per dose of misoprostol
  • Insufficient data to advise change in dosing interval

KEY POINTS:

• Prior to starting an induction of labor, contraindications should be reviewed
• Cervical ripening is recommended with a Bishop score of ≤6
• Predictors of induction success
  • Lower BMI | Greater dilation | Higher parity | Term gestational age
• Pharmacologic and non-pharmacologic methods can be used for induction based on the patient’s characteristics
• Misoprostol regimens are recommended for intrauterine fetal demise including TOLAC
• There is no strong consensus to define failed induction
  • At least 12 to 18 hours of latent labor with oxytocin and AROM should be allowed before diagnosing failed induction

Learn More – Primary Sources:

ACOG Practice Bulletin 107: Induction of Labor

Society of Family Planning: Interruption of nonviable pregnancies of 24–28 weeks’ gestation using medical methods

Related ObG Topics:

The ARRIVE Trial and Professional Guidance: Elective 39 Week Induction to Reduce the Risk of Cesarean Section

ACOG Recommendations: When to Deliver Medically Complicated Pregnancies

Stillbirth Management: The ACOG SMFM Consensus Document

Induction vs Expectant Management At and Beyond Term – the Cochrane Review

2020 Cochrane Review Update: How Does Membrane Sweeping Compare to Other Methods of Induction?

2021 Cochrane Review: Oral Misoprostol vs Other Labor Induction Methods

Cochrane Review Update: Safety and Effectiveness of Mechanical vs Pharmacological Methods of Labor Induction

Meta-analysis: Safety of Balloon Catheter for Induction in the Setting of Ruptured Membranes