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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Post-term Pregnancy and Induction of Labor
Sponsored by The Indian Health Service Clinical Support Center
7 Preinduction
Prior to induction, the cervix should be assessed and a modified Bishop score assigned. Points of 0-3 are given for each of 5 factors (see below). As noted above, prostaglandin preparations may change these values significantly.
- Scores >8 are associated with a likelihood of vaginal delivery similar to those seen with spontaneous labor.
- Scores <4 are associated with prolonged labor and a high incidence of failed induction and cesarean delivery.
Bishop Score
| Score | Dilation (cm) | Effacement (%) | Station (-3 to +3) | Consistency | Position |
| 0 | closed | 0-25 | -3 | firm | posterior |
| 1 | 1-2 | 25-50 | -2 | medium | mid |
| 2 | 3-4 | 50-75 | -1/0 | soft | anterior |
| 3 | >5 | >75 | +1/+2 | ---- | ---- |
Various methods are available for ripening the unfavorable cervix.
Mechanical methods
Intracervical placement of mechanical dilators, either a Foley catheter with a 30 mL bulb, or hygroscopic dilators (laminaria), are effective.
Pharmacologic
Prostaglandin E2 preparations compounded locally in your pharmacy using 20mg suppositories are subject to significant variability in efficacy and are probably best avoided if possible. A gel is now available in a 2.5 mL syringe that contains 0.5 mg of dinoprostone (Prepidil) for intracervical use. The gel can also be administered intravaginally employing a 2-5 mg dose. A 10 mg dinoprostone vaginal insert (Cervidil) is also very convenient. These preparations are relatively expensive, but usually effective.
Misoprostol 25-50 micrograms (1/4-1/2 of a 100 mcg tablet of Cytotec) is inexpensive and effective, but it is sometimes difficult to cut the unscored tablet and get accurate dosing. Patients should be monitored for at least an hour after placement. The ripening agent is typically utilized for 6-12 hours prior to induction.
How about outpatient cervical ripening?
Only a few small trials of outpatient cervical ripening have been reported. Of these, 5 investigated the use of prostaglandin gel preparations, two looked at mechanical dilating agents, and two misoprostol. The two randomized trials investigated vaginal misoprostol at a dose of 25 mcg in a total of 84 women.
Women in the first trial (Stitely et al )were given misoprostol 25 mcg vaginally qd over 48 hours (2 doses 24 hours apart) as a ripening agent. Approximately 55% the patients went into labor within 24 hours, and 89% within 48 hours, with a mean first dose to delivery interval of 36 hours. If the patient did not go into spontaneous labor by 72 hours she was admitted for formal induction. Four hours of monitoring post administration was carried out. Two episodes of transient, spontaneously resolving FHR decelerations occurred in the miso group and one in the placebo group. This was comparable to the occurrence in the PGE studies and to the 7% rate seen in the largest 25 mcg misoprostol inpatient induction study (Wing et al
) Since vaginally administered misoprostol peaks in 1-2 hours (Danielsson et al), and maintains that level for up to 4 hours, the 4-hour monitoring period seems conservative and prudent and should provide safety.
The second trial by Incerpi et al randomized women to receive 25 mcg of vaginal misoprostol or placebo on days 1 and 4 of a 7-day outpatient protocol. Approximately half the women in each group went into labor over this interval, so this doesn’t seem like a terribly useful protocol, although it also was safe.
Bottomline for outpatient ripening
At this point there is very limited data on outpatient cervical ripening. If one wants to pursue this, then it can be accomplished in settings with appropriate infrastructure and clear clinical guidelines using low dose therapy with the criteria listed above. An ongoing quality assurance audit should also be initiated and monitored.
Prior cesarean delivery
Cervical ripening is not contraindicated in patients with a prior cesarean who desire a trial of labor, but caution should be employed. Lydon-Rochelle et al found use of prostaglandin preparations for patients with a scarred uterus is associated with a significant increase in the incidence of uterine rupture (1.3% vs. 0.4%). Although the type of prostaglandin utilized was not specified in these studies, dinoprostone (prostaglandin E2) is significantly less potent than misoprostol (prostaglandin E1), and may be safer, but no comparison trials have been done. Any of these agents, and especially misoprostol, may induce labor rather than ripen the cervix, and this is especially true for patients with intermediate Bishop scores (5-7).
Bottomline: prior cesarean delivery and cervical ripening
Mechanical ripening or oxytocin are better options for women with a prior cesarean delivery.
