Objective: To examine serum relaxin as a predictor of spontaneous preterm delivery.
Study design: A prospective study of 2846 women with singleton pregnancies, from which a matched case-control study (84 cases of spontaneous preterm delivery before 37 weeks gestation and 175 controls) and a cohort (84 preterm and 399 term deliveries) were extracted.
Results: In the women with a subsequent preterm delivery the relaxin level decreased by 0.9% per week as compared to 1.9% per week (t-test, p=0.004) in the women with term deliveries. From the cohort the course of S-relaxin during pregnancy in both preterm and term deliveries were fitted and graphed. S-relaxin level was raised in women who were hormonally stimulated to obtain pregnancy (p=0.0001), and lower in women with pre-pregnancy overweight (BMI> or =25, p=0.01) as well as in women, who had previously been pregnant (p=0.008). A longitudinal adjusted model for the prediction of preterm delivery based on the change in S-relaxin was established.
Conclusions: S-relaxin levels decrease less rapidly in women who subsequently deliver preterm; this results in elevated S-relaxin levels in the second and the third trimesters.