Human preterm birth is associated with systemic and local changes in progesterone/17β-estradiol ratios

OBJECTIVE: The purpose of this study was to determine whether human preterm birth is associated with changes in 17β-estradiol and progesterone concentrations in maternal plasma and amniotic fluid. STUDY DESIGN: Forty healthy women in preterm labor with singleton pregnancies and intact membranes at 32 to 36 weeks of gestation who underwent amniocentesis for evaluation of the microbiologic status of the amniotic cavity were classified into the following two groups: 20 women who were delivered within 1 week from the amniocentesis (preterm delivery group) and 20 who were delivered at term (term delivery group). Maternal plasma and amniotic fluid concentrations of progesterone and 17β-estradiol were measured with sensitive and specific commercially available radioimmunoassay kits. RESULTS: The median amniotic fluid concentration of 17β-estradiol was significantly higher in women delivered prematurely than in those who were delivered at term (1.5 ng/ml vs 0.9 ng/ml, p = 0.0001). Moreover, the median plasma 17β-estradiol concentration was also significantly higher in the preterm delivery group than in the term group (14.1 ng/ml vs 6.9 ng/ml, p = 0.022). In contrast, no significant difference was found in amniotic fluid and plasma concentrations of progesterone between these two groups (24.5 ng/ml vs 27.5 ng/ml and 132.0 ng/ml vs 107.5 ng/ml, respectively). The median amniotic fluid progesterone/17β-estradiol ratio was significantly lower in the preterm delivery group than in those delivered at term (18.4 vs 33.6, respectively, p = 0.0017). Moreover, the median plasma progesterone/17β-estradiol ratio was also significantly lower in the preterm delivery group than in the term group (9.8 vs 17.0, respectively, p = 0.016). CONCLUSION: Human preterm birth is associated with significantly lower progesterone/17β-estradiol ratios than those of women with preterm labor delivered at term.