Association between raised serum relaxin levels during the eighteenth gestational week and very preterm delivery.

Objective: Our aim was to evaluate a possible association between serum relaxin levels in the 18th gestational week and preterm delivery.

Study Design: We conducted a nested case-control study that was based on serum samples obtained in the 18th week of gestation from 1545 unselected healthy primiparous women. Eleven case subjects were delivered very early (9 spontaneously, 2 by indicated cesarean delivery) and 42 moderately early (41 spontaneously, 1 by indicated cesarean delivery); 123 control subjects (121 having spontaneous labor, 2 undergoing indicated cesarean delivery) were randomly selected among the women with delivery at term.

Results: The serum relaxin concentration during the 18th gestational week was 63% higher among subjects with very preterm deliveries than among control subjects (P = .01, Mann-Whitney test). High relaxin levels during the 18th gestational week were associated with an increased risk of very preterm delivery (odds ratio, 11.3; 95% confidence interval, 2.14-59.1) and spontaneous very preterm delivery (odds ratio, 5.5; 95% confidence interval, 1.3-23). There was a negative correlation for case subjects and control subjects between serum relaxin concentrations during the 18th gestational week and gestational age at delivery (P < .05).

Conclusion: Serum relaxin may be an independent predictor when identification of women at risk of very preterm delivery is attempted in the 18th gestational week.