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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Post-term Pregnancy and Induction of Labor
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8 Induction
Depending on the cervical change effected by the ripening agent you’ve chosen, a plan for induction may be made. It is prudent to electronically monitor all post-term patients, although this may be done intermittently if the initial monitoring is reassuring.
Amniotomy
Women who have experienced significant dilation and effacement, in whom the cephalic presenting part is at a safe station, may undergo amniotomy (“surgical induction”). Some of these women will proceed into active labor with that intervention alone, whereas others will need further stimulation.
Oxytocin
Oxytocin may be given via a low dose protocol beginning at 2 mU/min and increasing by 2 mU/min every 15 minutes until effective contractions are occurring every 2-5 minutes.
Alternatively it may be given in an "active management" protocol (begin at 6 mU/min and increase by 6 mU/min q 15 minutes until 7 contractions in 15 minutes are achieved). Patient characteristics (parity, uterine over-distention, uterine scar) should dictate which dosing schedule is more appropriate for a particular patient.
Prostaglandins
If, on the other hand, the cervical changes have been less dramatic, and the cervix is softened, but still relatively thick and not dilated, misoprostol may be the more appropriate choice of agent. Vaginal misoprostol 25-50 micrograms (1/4 to1/2 of a 100 mcg tablet of Cytotec) high in the vaginal fornix q4h is usually safe and effective.
Vaginal misoprostol 25-50 micrograms (1/4 to1/2 of a 100 mcg tablet of Cytotec) high in the vaginal fornix q4h is usually safe and effective. Patients should remain recumbent for 1 hour after the tablet fragment is placed. The absorption of the tablet may be impaired by lubricating gel, so simply moistening it with tap water is recommended prior to insertion.
Alternatively, misoprostol at a dose of 25-100 mcg may be given orally q2h. Danielsson et al found that oral misoprostol reaches peak levels in 30-60 minutes, and is essentially gone by 2 hours, whereas vaginally administered misoprostol doesn’t reach peak levels until 1 hour, and these levels are then sustained for 4-6 hours. Vaginal and oral misoprostol should probably not be given simultaneously, because of these absorption kinetics.
Patients who do not have a good response to misoprostol may be switched to oxytocin after a 4-hour hiatus. Serial induction may be considered on a case by case basis, taking into consideration patient preference.
Uterine tachysystole vs Uterine hyperstimulation
Uterine hyperstimulation is always a concern when labor is stimulated. There is a difference between uterine tachysystole, which just means frequent contractions, and uterine hyperstimulation, which connotes an adverse effect on the FHR tracing. There is often disagreement about the exact definitions.
On the other hand the best definitions may not actually matter if the pattern concerns your colleagues on L/D….but let’s try to use a standardized definition, so that we are “comparing apples to apples”.
Crane et al defines:
- uterine tachysystole as a contraction frequency of more than five within 10 minutes for two consecutive 10-minute periods.
- uterine hyperstimulation as exaggerated uterine response with late FHR decelerations or fetal tachycardia greater than 160 beats per minute or other worrisome FHR changes.
Tachysystole or hyperstimulation was judged by Crane et al to occur if at least two of three graph MFM reviewers agreed with the diagnosis
If fetal intolerance of induced labor should occur, the oxytocin should be discontinued, or the misoprostol tablets removed (if they have not already dissolved), and fluids, lateralization, and a tocolytic such as terbutaline 0.25 mg IV or SQ should be given.
