The concentration of surfactant protein-A in amniotic fluid decreases in spontaneous human parturition at term.
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.
Chaiworapongsa
Tinnakorn
T
Perinatology Research Branch, NICHD/NIH/DHHS, Bethesda, Maryland, USA.
Hong
Joon-Seok
JS
Hull
William M
WM
Kim
Chong Jai
CJ
Gomez
Ricardo
R
Mazor
Moshe
M
Romero
Roberto
R
Whitsett
Jeffrey A
JA
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*
D037662:Pulmonary Surfactant-Associated Protein A; D037701:Pulmonary Surfactant-Associated Protein B