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CURRENT PRACTICE

The majority of inductions in the West Midlands are done using prostaglandin E2 (Prostin) for cervical ripening and amniotomy followed by oxytocin infusion. According to the Cochrane (1) review, PGE2 improves the Bishop's Score whilst decreasing the length of labour and the Caesarian section rate. The manufacturer's recommendation of repeat application have found their way into many labour ward protocols but may contribute to the frequent instances of uterine hyperstimulation (see below). A randomised comparison (2) found no clinical advantages in applying two vs one dose only of PGE2, and observed that two doses were more likely to result in passage of meconium and admission to neonatal intensive care.

OTHER METHODS

Mechanical methods such as hygroscopic dilators (3) and Foley's catheters (4) - appear as effective as intracervical gels at ripening the cervix . Regular 'stretch and sweep' from 39 weeks may reduce the number of women who reach 41 weeks gestation (5) but can result in discomfort and bleeding, and a recent systematic review (6) failed to find appreciable benefits.

NEW METHODS

Dinoprostone (Propess (7), Cervidil) has a mechanism which slowly releases 10mg of prostaglandin E2 over 12-24 hours. It has a thread which enables it to be removed if uterine hyperstimulation occurs. It has been used in America, but its hoped application as an outpatient cervical ripening agent is doubtful because of high removal rates after onset of contractions (8).

Mifepristone (RU486) is a progesterone antagonist used in therapeutic abortions. There is recent work to suggest that its cervical softening properties can also be applied for induction of labour (9) at term. A recent randomized trial (10) showed a modest effect on cervical ripening when given 24 hours before labor induction, appearing to reduce the need for misoprostol and oxytocin compared with placebo. However, there were also more non-reassuring fetal heart rate patterns and uterine contractile abnormalities occurred in mifepristone-treated subjects (11)

Misoprostol is a PGE1 analogue which is being used for 1st and 2nd trimester terminations, although it is not yet licensed for this use. For induction of labour, there is evidence of shorter labour-to-induction intervals with less need for formal amniotomy and oxytocin augmentation, but also a higher incidence of uterine hyperstimulation. ( 12 13). A large RCT is awaited to determine the optimum dosage. Misoprostol is heat stable and, unlike Prostin, does not require refrigeration and has a long shelf life. This and its lower unit cost would make it particularly attractive for use in developing countries.

References

1. Oxford Database of Perinatal Trials. Cochrane Pregnancy and Child Birth Data Base:  Oxford.

2. MacKenzie IZ, Burns E (1997) "Randomised trial of one versus two doses of prostaglandin E2 for induction of labour:1. Clinical outcome." Br J Obstet Gynaecol 1997 Sep;104(9):1062-7,Abstract

3. Sanchez-Ramos L, Kaunitz AM, Connor PM, (1992), "Hygroscopic cervical dilators and prostaglandin E2 gel for preinduction cervical ripening. A randomized, prospective comparison," J Reprod Med 1992 Apr;37(4):355-9, Abstract

4. St Onge RD, Connors GT, (1995), "Preinduction cervical ripening: a comparison of intracervical prostaglandin E2 gel versus the Foley catheter." Am J Obstet Gynecol, Feb;172(2 Pt 1):687-90, Abstract

5. Cammu H, Haitsma V, (1998), Sweeping of the membranes at 39 weeks in nulliparous women: a randomised controlled trial. Br J Obstet Gynaecol Jan;105(1):41-4, Abstract

6. Boulvain M, Irion O, (2000), Stripping/sweeping the membranes for inducing labour or preventing post-term pregnancy. Cochrane Database Syst Rev 2000;(2):CD000451, Abstract

7. Calder AA. Review of prostaglandin use in labour induction. Br J Obstet Gynaecol 104(S15):1997;8-12.

8. Rayburn WF, Tassone S, Pearman C, (2000), "Is cervidil appropriate for outpatient cervical ripening?" Obstet Gynecol, Apr 1;95(4 Suppl 1):S63, Abstract

9. Elliott CL, Brennand JE, Calder AA, (1998),The effects of mifepristone on cervical ripening and labor induction in primigravidae. Obstet Gynecol Nov;92(5):804-9, Abstract

10. Wing DA, Fassett MJ, Mishell DR, (2000), Mifepristone for preinduction cervical ripening beyond 41 weeks' gestation: a randomized controlled trial. Obstet Gynecol Oct 1;96(4):543-548, Abstract

11. Wing DA, Fassett MJ, Mishell DR, (2000), Mifepristone for preinduction cervical ripening beyond 41 weeks' gestation: a randomized controlled trial. Obstet Gynecol Oct 1;96(4):543-548, Abstract

12. Wing DA, 1999,Labor induction with misoprostol. Am J Obstet Gynecol Aug;181(2):339-45, Abstract

13. Sanchez-Ramos L, Kaunitz AM, Wears RL, Delke I, Gaudier FL, (1997), "Misoprostol for cervical ripening and labor induction: a meta-analysis." Obstet Gynecol Apr;89(4):633-42, Abstract