Follistatin-free activin A is not associated with preterm birth

OBJECTIVE: The purpose of this study was to determine whether follistatin-free activin A (an inhibin-related protein with rising serum levels before term labor) is associated with spontaneous preterm birth in an outpatient population. STUDY DESIGN: From 10 centers, 2929 women were enrolled in the Preterm Prediction Study. Plasma was isolated from blood samples obtained at 24 and 28 weeks of gestation and stored. A nested case-controlled study was performed; there were 197 women with spontaneous preterm birth before 37 weeks of gestation with 24-week samples and 142 cases with 28-week samples that were matched to an equal number of term control samples from each time point. A follistatin-free activin A enzyme-linked immunosorbent assay was performed, with results interpreted as positive or negative (defined as a value less than the assay limit of sensitivity). A comparison of follistatin-free activin A with other tests that were associated with spontaneous preterm birth (α-fetoprotein, alkaline phosphatase, cortisol, granulocyte colony-stimulating factor, fetal fibronectin, and cervical interleukin-6) was also performed. RESULTS: The odds ratio for associated spontaneous preterm birth at <37 weeks of gestation if the follistatin-free activin A result was positive was 1.16 at 24 weeks (95% CI, 0.62-2.17) and 1.39 at 28 weeks (95% CI, 0.68-2.84). A positive follistatin-free activin A result at either 24 or 28 weeks was not associated with a positive test for any of the other laboratory tests, except granulocyte colony-stimulating factor at 28 weeksʹ gestation. CONCLUSION: Follistatin-free activin A is not associated with spontaneous preterm birth in an asymptomatic outpatient population. Follistatin-free activin A may not be an appropriate screening marker for spontaneous preterm birth in the office setting. (Am J Obstet Gynecol 2002;186:464-9.)