What is induction of labor?
Induction of labor is the use of medications or other methods to
start uterine
contractions before the natural onset of labor in order to have a vaginal
delivery.
Why is induction of labor done?
Induction of labor is usually considered
when continuing the pregnancy would increase the risks to the baby or mother without giving any benefit to either.
Some Medical Reasons for Induction [1-3]
Nonmedical (Elective) Reasons for Induction
- The mother is uncomfortable or anxious
- Partner soon leaving town (including
military deployment)
- Family in town
-
The
mother has rapid deliveries.
- Mother lives a long distance from the hospital,
The National Institute of Child Health and Human
Development, Society for Maternal-Fetal Medicine, and American College of
Obstetricians and Gynecologists recommend[4]
-
Labor induction should be performed only for medical
indications
- If done for nonmedical indications, the gestational age should be 39 weeks or more, and the
cervix should be favorable (Bishop score 8 or higher), especially in a woman
who has never given birth (nulliparous).
- Cervical ripening may be considered when there is a
medical indication for induction.
-
Since inductions without medical indication should not be done with an unripe
cervix, cervical ripening would not be an option
What is a Bishop Score and what is
a favorable (ripe) or an unfavorable (unripe) cervix?
[1,5]The Bishop Score (also known as Pelvic Score) is the most
commonly used method to assess the readiness of the cervix for induction of
labor. The Bishop Score gives points to 5 components of the pelvic examination
dilation, effacement of the cervix, station of the fetus, consistency of the
cervix, and position of the cervix.
CERVICAL EXAM |
SCORE |
0 |
1 |
2 |
3 |
Dilation (cm) |
Closed
|
1-2 cm
|
3-4cm
|
5 -6 cm
|
Effacement (%) |
0-30%
|
40-50%
|
60-70%
|
80%
|
Station |
-3
|
-2
|
-1 or 0
|
+1, +2
|
Consistency |
Firm
|
Medium
|
Soft
|
|
Position |
Posterior |
Mid |
Anterior |
|
If the Bishop score is 8 or greater the chances of having a vaginal delivery are
good and the cervix is said to be favorable or "ripe" for induction.
If the
Bishop score is 6 or less the chances of having a vaginal delivery are low and
the cervix is said to be unfavorable or "unripe" for induction.
See Bishop Score
Calculator for more on the Bishop Score
What is cervical ripening?
Cervical ripening is the process where the cervix becomes ready for labor
by becoming softer , thinner and opening (dilating) during the last few weeks of
pregnancy. Medications or mechanical dilators are sometimes used to artificially
ripen the cervix before induction to make the cervix more favorable and a
vaginal delivery more likely.
What are some methods that are used to ripen the cervix?[1,
7-16, 30]
What are some methods that can be used to induce
labor? [1]
-
Oxytocin is a hormone that is made in the brain and causes the uterus to
contract Oxytocin is released naturally into the blood
during labor, nipple stimulation, and sex.
Synthetic oxytocin (Pitocin) is used to begin or stimulate labor [6]
-
Amniotomy also known as artificial rupturing of the membranes (AROM) or
breaking your water. The procedure is sometimes done using a plastic
device that looks like a crochet needle (AmniHook® ) to open the
water bag that surrounds the baby. Amniotomy used alone for inducing
labor can be unpredictable . Amniotomy is more effective in speeding up the
progress of labor when used with oxytocin. [31,32]
What are the risks of inducing labor?
-
The induction may fail and you will need to be delivered by cesarean
section.
Failed induction was found to be more likely with an unfavorable cervix in a
woman who has never given birth (nulliparous) in some but not all studies
[37].
The NICHD, SMFM, and ACOG recommend
"The diagnosis of failed induction should only be made after an adequate
attempt. Failed induction is defined as failure to generate regular (eg, every 3
minutes) contractions and cervical change after at least 24 hours of oxytocin
administration, with artificial membrane rupture if feasible."
- Abnormal contraction pattern.
Prostaglandins and oxytocin may
cause contractions that last too long are too strong or are too close
together. The abnormal contractions can cause your baby's heart
rate to drop.
-
Cord prolapse [33]
The umbilical cord is the tube-like structure attached to your
developing baby's belly that supplies nutrients and oxygen to your baby.
Sometimes after the membranes have ruptured the baby's umbilical cord may
pass through the cervix (the opening of the uterus) in front of the head or
body of your baby. This called cord prolapse. Pressure on the
umbilical cord can decrease the blood flow to the baby causing the baby's
heart rate to drop.
- Bleeding and Pain [34]
Bleeding and pain may be caused by mechanical methods such as the foley
catheter or dilators.
- Infection
An increased risk for maternal and neonatal infections has been reported
in connection with the use mechanical devices
-
Uterine Rupture
[17,18]
Uterine rupture is a tear through the entire thickness of the uterine wall.
Uterine rupture usually occurs in a woman who has had an operation on her uterus such as a
cesarean section, myomectomy (removal of fibroids) , or metroplasty (repair of
uterine malformation). Although uterine rupture may occur even with
natural labor the chances of uterine rupture occurring iare greater if
prostaglandins are used to induce
labor.
-
Amniotic Fluid Embolism [19-21]
Amniotic fluid embolism (AFE ) is a rare unpredictable condition in which
amniotic fluid , the fluid around the baby, enters the mother's blood stream and
causes heart and lung failure with uncontrolled bleeding. AFE has been associated
with advanced maternal age, polyhydramnios, cervical laceration, uterine
rupture, placenta previa , abruption, eclampsia, fetal distress , cesarean
delivery, and in some studies induction of labor.
Can you be induced if you are having a vaginal birth after
cesarean delivery (VBAC)?[22-36]
Induction of labor
for medical reasons may be an option for women who wish to attempt a vaginal
birth after having had a cesarean delivery (VBAC) . If you are attempting a VBAC
you should know that you are more likely to have a cesarean section with
induction of labor. In addition induction of labor with oxytocin or
prostaglandins has been associated with an increased risk of uterine rupture in
women attempting VBAC in some studies. ACOG recommends "Misoprostol should
not be used for third trimester cervical ripening or labor induction in patients
who have had a cesarean delivery or major uterine surgery." The Society of
Obstetricians and Gynaecologists of Canada. (SOGC) considers cervical ripening
with a transcervical foley catheter a safer option in women planning VBAC.
However, the risk of uterine rupture is not entirely eliminated with the use of
the Foley catheter .
More Questions
Reviewed by Mark Curran, M.D. FACOG
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