Objective: To investigate the effect of corticotropin-releasing hormone (CRH), cortisol and dehydroepiandrosterone sulfate in pathogenesis of preterm labor.

Methods: A cross-sectional study was conducted including 80 pregnant women in the following categories: (1) preterm delivery in labor (PL, n=26), (2) term in labor (TL, n=29), (3) term not in labor (n=25). The expression and localizations of CRH mRNA in placentas and fetal membranes in three groups respectively were examined by in situ hybridization. Radioimmunoassay was used to detect the levels of corticotropin releasing hormone, cortisol and dehydroepiandrosterone sulfate in fetal umbilical cord blood in three groups.

Results: (1) By in situ hybridization, we localized CRH mRNA to the syncytiotrophoblasts of placenta, the amniotic epithelial cells and chorion cells. (2) The positive index of expression of CRH mRNA in fetal membranes of PL (5.4 +/- 1.4) and TL, (5.4 +/- 1.5) was higher than that in term not in labor, (2.0 +/- 1.4, P<0.01). And there was no difference between PL and TL (P>0.05). The positive index of expression of CRH mRNA in placentas of PL (5.5 +/- 1.4) and TL (5.4 +/- 1.5) was higher than that in term not in labor (2.7 +/- 1.5, P<0.01). And there was no difference between PL and TL (P>0.05). The expression of CRH mRNA was not distinct between placentas and fetal membranes in three groups (P>0.05). (3) The levels of CRH and DHEA-S in umbilical cord blood of PL (7.8 +/- 3.3) ng/L, and (514 +/- 295) microg/L, respectively and of TL (7.7 +/- 4.1) ng/L, and (483 +/- 207) microg/L, were higher than that in term not in labor (4.8 +/- 2.4) ng/L, and (360 +/- 80) microg/L, respectively (P<0.05). And there was no difference between PL and TL (P>0.05). In PL, the level of CRH in umbilical cord blood and the expression of CRH mRNA in placentas and fetal membranes were correlated with each other (r=0.935 and 0.853, P<0.01). Also in TL, the levels of CRH and CRH mRNA were correlated with each other (r=0.902 and 0.825, P<0.01). (4) The level of cortisol in umbilical cord blood of PL (246 +/- 117) microg/L was higher than that in TL (172 +/- 72) microg/L (P<0.05) and term not in labor (126 +/- 60) microg/L (P<0.01). And the levels of cortisol in umbilical cord blood of TL were higher than that in term not in labor (P<0.05). In PL, the levels of CRH and cortisol and dehydroepiandrosterone sulfate in umbilical cord blood were correlated respectively with each other (r=0.523 and 0.424, P<0.05), and in TL the level of CRH was correlated with cortisol and dehydroepiandrosterone sulfate respectively (r=0.438 and 0.354, P<0.05).

Conclusions: (1) CRH may participate in onset of labor. Increase in CRH may be an important stimulator of preterm labor. (2) Cortisol and dehydroepiandrosterone sulfate play an important role in the initiation of labor.