Induction of Labor
Induction of labor refers to stimulation of uterine contractions prior to the onset of spontaneous labor.
Indications for labor induction:
A. Preeclampsia/eclampsia, and other hypertensive diseases
B. Maternal diabetes mellitus
C. Prelabor rupture of membranes
E. Intrauterine fetal growth restriction (IUGR)
G. In-utero fetal demise
H. Postterm pregnancy
Absolute contraindications to labor induction:
A. Prior classical uterine incision
B. Active genital herpes infection
C. Placenta or vasa previa
D. Umbilical cord prolapse
E. Fetal malpresentation, such as transverse lie
Requirements for induction
Prior to undertaking labor induction, assessments of gestational age, fetal size and presentation, clinical pelvimetry, and cervical examination should be performed. Fetal maturity should be evaluated, and amniocentesis for fetal lung maturity may be needed prior to induction.
Clinical criteria that confirm term gestation:
Fetal heart tones documented for 30 weeks by Doppler.
Thirty-six weeks have elapsed since a serum or urine human chorionic gonadotropin (hCG) pregnancy test was positive.
Ultrasound measurement of the crown-rump length at 6 to 11 weeks of gestation or biparietal diameter/femur length at 12 to 20 weeks of gestation support a clinically determined gestational age equal to or greater than 39 weeks.
Assessment of cervical ripeness:
A cervical examination should be performed before initiating attempts at labor induction.
The modified Bishop scoring system is most commonly used to assess the cervix. A score is calculated based upon the station of the presenting part and cervical dilatation, effacement, consistency, and position.
The likelihood of a vaginal delivery after labor induction is similar to that after spontaneous onset of labor if the Bishop score is >8.
Induction of labor with oxytocin
The uterine response to exogenous oxytocin administration is periodic uterine contractions.
B. Oxytocin regimen (Pitocin)
Oxytocin is given intravenously. Oxytocin is diluted by placing 10 units in 1000 mL of normal saline, yielding an oxytocin concentration of 10 mU/mL.
Cervical ripening agents
A ripening process should be considered prior to use of oxytocin use when the cervix is unfavorable.
Membrane stripping is a widely utilized technique, which causes release of either prostaglandin F2-alpha from the decidua and adjacent membranes or prostaglandin E2 from the cervix. Weekly membrane stripping beginning at 38 weeks of gestation results in delivery within a shorter period of time (8.6 versus 15 days).
is an effective method of labor induction when performed in women with partially dilated and effaced cervices. Caution should be exercised to ensure that the fetal vertex is wellapplied to the cervix and the umbilical cord or other fetal part is not presenting.
Local administration of prostaglandins to the vagina or the endocervix is the route of choice because of fewer side effects and acceptable clinical response. Uncommon side effects include fever, chills, vomiting, and diarrhea.
contains 0.5 mg of dinoprostone in 2.5 mL of gel for intracervical administration. The dose can be repeated in 6 to 12 hours if there is inadequate
cervical change and minimal uterine activity following the first dose. The maximum cumulative dose is 1.5 mg (ie, 3 doses) within a 24-hour period. The time interval between the final dose and initiation of oxytocin should be 6 to 12 hours because of the potential for uterine hyperstimulation with concurrent oxytocin and prostaglandin administration.
is a vaginal insert containing 10 mg of dinoprostone in a timed-release formulation. The vaginal insert administers the medication at 0.3 mg/h and should be left in place for 12 hours. Oxytocin may be initiated 30 to 60 minutes after removal of the insert.
An advantage of the vaginal insert over the gel formulation is that the insert can be removed in cases of uterine hyperstimulation or abnormalities of the fetal heart rate tracing.
Complications of labor induction
Hyperstimulation and tachysystole
may occur with use of prostaglandin compounds or oxytocin. Hyperstimulation is defined as uterine contractions lasting at least two minutes or five or more uterine contractions in 10 minutes. Tachysystole is defined as six or more contractions in 20 minutes.
If oxytocin is being infused, it should be discontinued to achieve a reassuring fetal heart rate pattern. Placing the woman in the left lateral position, administering oxygen, and increasing intravenous fluids may also be of benefit.