title: 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.
  
  
  METHODS
  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 5.6 microg/mL, range 2.2-15.2 microg/mL vs. mid-trimester: median 1.64 microg/mL, range 0.1-4.7 microg/mL, and SP-B term no labor: median 0.54 microg/mL, range 0.17-1.99 microg/mL vs. mid-trimester: median 0 microg/mL, range 0-0.35 microg/mL; both p < 0.001). 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 2.7 microg/mL, range 1.2-10.1 microg/mL vs. term no labor: median 5.6 microg/mL, range 2.2-15.2 microg/mL; p < 0.001). 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 0.47 microg/mL, range 0.04-1.32 microg/mL vs. term no labor: median 0.54 microg/mL, range 0.17-1.99 microg/mL; p = 0.2).
  
  
  CONCLUSIONS
  The amniotic fluid concentration of SP-A decreases in spontaneous human parturition at term.
authors.affiliation: Perinatology Research Branch, NICHD/NIH/DHHS, Bethesda, Maryland, USA.
authors.forename: Tinnakorn
authors.initials: T
authors.lastname: Chaiworapongsa
authors.forename: Joon-Seok
authors.initials: JS
authors.lastname: Hong
authors.forename: William M
authors.initials: WM
authors.lastname: Hull
authors.forename: Chong Jai
authors.initials: CJ
authors.lastname: Kim
authors.forename: Ricardo
authors.initials: R
authors.lastname: Gomez
authors.forename: Moshe
authors.initials: M
authors.lastname: Mazor
authors.forename: Roberto
authors.initials: R
authors.lastname: Romero
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Whitsett
mesh_terms: D000328:Adult; D000653:Amniotic Fluid / Q000378:metabolism*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D011247:Pregnancy / Q000378:metabolism*; D037662:Pulmonary Surfactant-Associated Protein A / Q000378:metabolism*; D037701:Pulmonary Surfactant-Associated Protein B / Q000378:metabolism*; D047929:Term Birth / Q000378:metabolism*
chemical_list: D037662:Pulmonary Surfactant-Associated Protein A; D037701:Pulmonary Surfactant-Associated Protein B