The concentration of surfactant protein - A in amniotic fluid decreases in spontaneous human parturition at term

Abstract

Objective. The fetus is thought to play a central role in the onset of labor. Pulmonary surfactant protein (SP)-A, secreted by the maturing fetal lung, has been implicated in the mechanisms initiating parturition in mice. The present study was conducted to determine whether amniotic fluid concentrations of SP-A and SP-B change during human parturition. Study design. Amniotic fluid SP-A and SP-B concentrations were measured with a sensitive and specific ELISA in the following groups of pregnant women: (1) mid-trimester of pregnancy, between 15 and 18 weeks of gestation (n=29), (2) term pregnancy not in labor (n=28), and (3) term pregnancy in spontaneous labor (n=26). Non-parametric statistics were used for analysis. Results. SP-A was detected in all amniotic fluid samples. SP-B was detected in 24.1% (7/29) of mid-trimester samples and in all samples at term. The median amniotic fluid concentrations of SP-A and SP-B were significantly higher in women at term than in women in the mid-trimester (SP-A term no labor: median 5.6g/mL, range 2.2-15.2g/mL vs. mid-trimester: median 1.64g/mL, range 0.1-4.7g/mL, and SP-B term no labor: median 0.54g/mL, range 0.17-1.99g/mL vs. mid-trimester: median 0g/mL, range 0-0.35g/mL; both p0.001). The median amniotic fluid SP-A concentration in women at term in labor was significantly lower than that in women at term not in labor (term in labor: median 2.7g/mL, range 1.2-10.1g/mL vs. term no labor: median 5.6g/mL, range 2.2-15.2g/mL; p0.001). There was no significant difference in the median amniotic fluid SP-B concentrations between women in labor and those not in labor (term in labor: median 0.47g/mL, range 0.04-1.32g/mL vs. term no labor: median 0.54g/mL, range 0.17-1.99g/mL; p=0.2). Conclusion. The amniotic fluid concentration of SP-A decreases in spontaneous human parturition at term.