Concentrations of serum total activin A and inhibin A in preterm and term labor patients: a cross-sectional study

To compare maternal serum levels of total activin A and inhibin A in preterm and term patients who are in labor or not in labor.

A cross-sectional study compared activin A and inhibin A in the following groups of patients: preterm and in labor (n = 65), preterm and not in labor (n = 96), term and in labor (n = 65), and term and not in labor (n = 65). Preterm was defined as 23-34 weeks' gestation and term as 37-42 weeks' gestation. Labor was defined as regular contractions with progressive cervical change or an initial examination revealing cervical dilation of 1-3 cm with 50% effacement or more. Follistatin levels were analyzed in a subset of 12 patients from each group. Analytes were measured by two-site enzyme-linked immunosorbent assays.

Activin A levels were higher in the preterm labor group (median 1.38 multiples of the median [MoM], interquartile range [IQR] 1.01 MoM) compared with the preterm nonlabor group (median 1.0 MoM, IQR 0.78 MoM, P <.05) and in the term labor group (median 1.37 MoM, IQR 1.74 MoM) compared with the term nonlabor group (median 1.0 MoM, IQR 0.87 MoM, P <.05). Inhibin A levels were higher in the preterm labor group (median 1.27 MoM, IQR 0.73 MoM) compared with the preterm nonlabor group (median 1.0 MoM, IQR 0.58 MoM, P <.05). Post-hoc analysis of activin A and inhibin A elevations in the preterm labor group revealed a significant effect only during 31-34 weeks' gestation. The total activin A:follistatin ratio, an indirect measure of free activin A, was similar between labor and nonlabor gestational age-matched patient groups.

Levels of total activin A and inhibin A were increased in patients during labor; however, based on the moderate degree and narrow gestational age range of the increased levels, these analytes are not likely to be clinically useful in predicting preterm labor.