Induction of labor is a common obstetric procedure performed for various medical reasons when continuing the pregnancy is riskier than delivering the baby. While many inductions result in vaginal deliveries, some end up requiring cesarean deliveries (C-sections). The rate of induction failures leading to C-sections varies depending on multiple factors.
What is labor induction?
Labor induction is the process of artificially starting labor before it begins naturally. It is performed when the benefits of delivering the baby outweigh the risks of continuing the pregnancy. Some common reasons for inducing labor include:
- The pregnancy lasting more than 42 weeks (post-term).
- Health issues in the mother such as high blood pressure or diabetes.
- Problems with the growth and development of the baby.
- Premature rupture of membranes without the onset of labor.
- Intrauterine fetal demise (the baby has passed away in the womb).
There are various methods used for labor induction including:
- Administering prostaglandin medications such as misoprostol.
- Breaking the amniotic sac (membranes) in a process called amniotomy.
- Using a Foley catheter balloon to mechanically dilate the cervix.
- Intravenous infusion of the hormone oxytocin (Pitocin) to cause contractions.
The method chosen depends on the condition of the cervix. If the cervix is already partially dilated and effaced, oxytocin augmentation alone may induce labor. With an unfavorable cervix, medications and mechanical dilators are generally needed first.
What percentage of inductions end in C-sections?
The rate of inductions resulting in C-sections varies between hospitals and patient populations but averages around 25%. Some key statistics on induction failure rates include:
- First-time mothers have a higher rate of emergency C-sections after induction compared to women who have had previous vaginal deliveries.
- One study found that 27.3% of first-time mothers undergoing induction required a C-section compared to 11.7% of women with previous vaginal deliveries.
- Women who have an unfavorable cervix at the start of induction are more likely to need a C-section. One study found a 39.1% C-section rate with an unfavorable cervix compared to 7.4% with a favorable cervix.
- Obesity and pregnancy complications like gestational diabetes also increase the likelihood that an induction will end in a C-section.
Overall, about one in four inductions fail to result in a vaginal delivery even after augmented labor. However, this rate varies significantly based on individual factors.
Factors that influence failed induction rates
Many factors impact whether an induction of labor will be successful or ultimately result in a C-section. The main factors include:
Parity
Parity refers to the number of previous viable pregnancies reaching 20 weeks. Women pregnant for the first time (nulliparous) have higher failed induction rates than multiparous women who have had previous births. Reasons include:
- The cervix of first-time mothers is less pliable and takes longer to efface and dilate.
- Previous vaginal deliveries encourage cervical ripening.
- Uterine muscles strengthen with successive pregnancies, increasing effectiveness of contractions.
Bishop score
The Bishop score is a pre-induction assessment of the cervix based on:
- Dilation – how much the cervix has opened, from 0-10 cm.
- Effacement – how much the cervix has thinned out, from 0%-100%.
- Station – the position of the presenting part in relation to the ischial spines, from -3 to +3.
- Consistency – firmness vs softness.
- Position – anterior vs posterior.
A higher Bishop score indicates a ripe, favorable cervix. Women with lower scores have higher C-section risks with induction.
Gestational age
The longer a pregnancy continues past 40 weeks, the higher the chance of successful induction due to increased uterine contractibility. Elective inductions before 39 weeks when the cervix is unfavorable have high failure rates.
Induction method
Some induction techniques like Foley catheters have higher C-section rates than medications like prostaglandins and oxytocin. Combining multiple methods (dual induction) increases the chance of vaginal delivery.
Birth weight
Babies with higher birth weights often fail to descend despite strong contractions. First-time mothers are at higher risk as the pelvic outlet has not been stretched by previous births.
Pregnancy complications
Conditions like gestational hypertension, preeclampsia, gestational diabetes and fetal growth problems increase emergency C-section risks due to distress.
Methods to reduce failed inductions
The following methods may help reduce failed labor inductions:
- Performing elective inductions only at 39 weeks or later for medical reasons.
- Using medications like prostaglandins to ripen the cervix before oxytocin induction.
- Having strict protocols for oxytocin administration and discontinuation if inadequate progress.
- Using deliberate, sequential induction steps matched to the Bishop score.
- Allowing longer labors in first-time mothers before diagnosing failure to progress.
- Encouraging operative vaginal deliveries like vacuum or forceps when appropriate.
- Having experienced obstetricians readily available for emergencies.
However, C-sections will still be necessary in many cases for maternal and fetal indications.
Risks of failed induction
Allowing labor to continue indefinitely after failed induction increases risks of complications including:
- Maternal exhaustion, emotional distress.
- Infection due to prolonged rupture of membranes.
- Postpartum hemorrhage due to uterine exhaustion.
- Fetal distress due to cord compression or placental insufficiency.
- Uterine rupture in women with previous C-sections attempting vaginal birth.
For this reason, time limits are set on the induction process before moving to a C-section if progress remains inadequate. This helps avoid potentially life-threatening complications.
Conclusion
Overall, approximately 25% of induced labors end in C-section, with higher rates among first-time mothers, unfavorable cervices, and pregnancy complications. Careful patient selection, standardized induction protocols, allowing longer labors in nulliparous women, and having experienced staff available can reduce the number of failed inductions. However, C-sections remain an important option when problems arise to prevent harm to both mother and baby.
