S-relaxin as a predictor of preterm delivery in women with symptoms of preterm labour.

Objective: To evaluate whether serum relaxin (S-relaxin) can predict spontaneous delivery before 34 weeks of gestation in high risk pregnancies.

Design: A prospective cohort study.

Setting: Calculated sample size was reached over a two-year period, during which 9507 women gave birth. Of these, 157 healthy women were eligible for the study as they were admitted with symptoms of delivery before 34 weeks of gestation. Ninety-three women were included. Overall participation rate was 59%.

Population: Healthy women with singleton pregnancies with symptoms of delivery before 34 weeks of gestation.

Methods: S-relaxin was measured using a standard sandwich ELISA.

Main Outcome Measures: End points were preterm delivery before 34 weeks of gestation and delivery within three days from initiation of symptoms. The best possible prediction of preterm delivery was established using logistic regression for risk factors individually associated with preterm delivery before 34 weeks of gestation. S-relaxin was dichotomised to obtain best possible fit and then entered into the model. The same analyses were done for delivery within three days.

Results: Median S-relaxin levels varied significantly in the women with preterm prelabour rupture of membranes (PPROM) (316 pg/mL), contractions (222 pg/mL) or ripe cervices (203 pg/mL) (P < 0.05). S-relaxin above the 80th centile (> or = 300 pg/mL) was associated with an increased risk of preterm delivery [crude OR = 4.8; (95% CI: 1.9-12)]. Likelihood ratio of a positive test is 2.6 (1.5-4.9) and S-relaxin resulted in a post-test probability of preterm delivery of 0.72, compared with a pre-test probability of 0.49. S-relaxin contributed to the identification of delivery within three days [adj. OR = 11 (95% CI: 1.8-64)].

Conclusion: S-relaxin may be a useful predictor in women with symptoms of delivery before 34 weeks of gestation.