Starting your OB/GYN residency? Or just trying to wrap your head around labor induction? Let’s break it all down in a way that’s easy to understand—and clinically useful.

Before we dive in, if you’re a fourth-year med student who just matched into OB/GYN, I’ve created a free resource just for you:

The OB/GYN Residency Starter Pack: A 5-Step Guide for Incoming Interns

It’s designed to help you feel more prepared and less overwhelmed before day one. Download it here to get your copy.

What is Induction of Labor?

Induction of labor means stimulating uterine contractions before spontaneous labor begins. Why do we do this? When the benefits of delivery outweigh the risks of continuing the pregnancy (or electively after 39w0d).

To review the common indications, check out ACOG Practice Bulletin #831: Medically Indicated Late Preterm and Early Term Deliveries.

The Two Phases of Induction

Induction can be thought of in two phases:

Phase 1: Cervical Ripening

The goal here is to soften, thin, and slightly dilate the cervix to prepare it for effective contractions.

We use the Bishop Score to assess how “favourable” the cervix is. It evaluates:

Dilation
Effacement
Station
Position
Consistency

There’s no universally agreed-upon “favorable” score—some studies use 6, others use 8—but generally, a score between 6–8 means the cervix is ready for Phase 2.

Phase 2: Induction of Labor

Once the cervix is favourable, we move to actually initiating labor with medications or procedures to start or strengthen contractions.

Phase 1: Cervical Ripening

Medical Methods

Misoprostol (Cytotec)

Synthetic prostaglandin E1
Administered orally, sublingually, or vaginally

Dinoprostone (Cervidil)

Synthetic prostaglandin E2
Vaginal insert or gel

Mechanical Methods

Single or Double Balloon Catheters (Foley or Cook)

Inserted through the cervix and inflated
Generally requires at least fingertip dilation
Can be combined with medication

Osmotic Dilators (Laminaria, Dilapan-S)

Expand in the cervical canal over time

Extra-Amniotic Saline Infusion (EASI)

Infuses saline between uterus and membranes

Membrane Stripping

Technically an induction method, but often done during ripening if cervix is dilated enough

Common Clinical Approach:

Start with misoprostol every 3-6 hours
Once patient reaches ~1 cm dilation, place a Foley or Cook balloon (and strip membranes if possible)
Balloon falls out at ~3–4 cm → move to Phase 2

Phase 2: Inducing Labor

Medical Methods

Oxytocin (Pitocin)

IV infusion
Generally titrated every 30 minutes
Goal: 5 contractions in 10 minutes or adequate MVUs if using an IUPC

Mechanical Methods

Amniotomy (Artificial Rupture of Membranes)

No strict rules about timing
Early amniotomy may shorten labor without increasing cesarean risk in patients with a favourable cervix

Nipple Stimulation

Not commonly used in hospitals
Mostly studied in low-risk pregnancies

Fun fact: One of my patients once nipple-stimmed her way from closed to 4 cm because she declined all other interventions!

Induction Scenarios (Clinical Examples)

1. G1P0, Induction for Preeclampsia Without Severe Features

Closed cervix → 4 vaginal misoprostol doses
Foley + membrane strip at 1 cm
Foley falls out → Bishop score 6
Pitocin + amniotomy → vaginal delivery

2. G4P3003, Induction for Advanced Maternal Age

Initial exam: 2/50/-3 → Foley + misoprostol
Balloon falls out → Bishop 5
Another miso dose → Bishop 7
Pitocin started → SROM → delivery

Anecdotal tip: Multiparous patients often don’t need perfect Bishop scores to respond to Pitocin + amniotomy!

3. G2P0101, Elective Term Induction

Closed cervix → Cervidil for 12 hours
1.5/20/-3 → Balloon + oral miso
Balloon falls out → Bishop 6
Amniotomy → contractions slow → Pitocin started → delivery

Key Takeaways

Induction = 2 phases: ripening (Phase 1) and actual induction (Phase 2)
Medical methods: misoprostol, dinoprostone, oxytocin
Mechanical methods: balloons, amniotomy
Bishop Score is your guide to timing and transition
Start with cervical ripening if cervix is unfavourable
Use Pitocin and/or amniotomy once favourable
Don’t forget to grab your free OB/GYN Residency Starter Pack—a 5-step guide to help you prepare before July 1.
Download it here