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Cochrane Database Syst Rev. 2001;(2):CD003103.

Relaxin for cervical ripening and induction of labour.

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Clinical Effectiveness Support Unit, Royal College of Obstetricians and Gynaecologists, 27 Sussex Place, Regent's Park, London, UK, NW1 4RG.



Relaxin is a protein hormone composed of two amino acid chains. The role played by relaxin in human pregnancy and parturition is unclear. Its use and involvement as a cervical ripening agent has been debated since the 1950s. Because the main source of human relaxin is the corpus luteum of pregnancy much of the early work on induction of labour has focused on porcine or bovine preparations. With the advent of DNA recombinant technology human relaxin has become available for evaluation. Relaxin is thought to have a promoting effect on cervical ripening. Due to a possible inhibitory effect on human myometrial activity, relaxin may not be associated with the concomitant increase in the rate of uterine hyperstimulation seen with other induction agents. This is one of a series of reviews of methods of cervical ripening and labour induction using a standardised methodology.


To determine the effects of relaxin (both purified porcine and recombinant human) for third trimester cervical ripening or induction of labour in comparison with other methods of induction.


The Cochrane Pregnancy and Childbirth Group trials register, the Cochrane Controlled trials register and bibliographies of relevant papers. Last searched: November 2000.


(1) clinical trials comparing relaxin used for third trimester cervical ripening or labour induction with placebo/no treatment or other methods listed above it on a predefined list of labour induction methods; (2) random allocation to the treatment or control group; (3) adequate allocation concealment; (4) violations of allocated management not sufficient to materially affect conclusions; (5) clinically meaningful outcome measures reported; (6) data available for analysis according to the random allocation; (7) missing data insufficient to materially affect the conclusion.


A strategy has been developed to deal with the large volume and complexity of trial data relating to labour induction. This involves a two-stage method of data extraction.


In total, nine studies were considered; five have been excluded and four included examining a total of 267 women. There were no reported cases of uterine hyperstimulation with fetal heart rate changes in any of the studies. The rate of caesarean section was not different in those women given relaxin compared with placebo (15.3% versus 14.2%; relative risk (RR) 0.79, 95% confidence interval (CI) 0.42,1.50). There was a reduction in the risk of the cervix remaining unfavourable or unchanged with induction with relaxin (21.9% versus 49.3%; RR 0.45, 95% CI 0.28,0.72). There were no reported cases of uterine hyperstimulation without FHR changes.


The place of relaxin, either purified porcine or recombinant human, as an induction or cervical priming agent is unclear. Further trials are needed to estimate the true effect of relaxin within current clinical practice.

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