Amniotic fluid concentration of retinol-binding protein 4 (RBP4) among women with spontaneous preterm labor and intact membranes (PTL). The median amniotic fluid RBP4 concentration was higher in patients with intra-amniotic infection/inflammation (IAI) than in women with PTL without IAI who delivered preterm [1268.9 ng/mL, interquartile range (IQR) 900.3-1970.1 vs. 815.8 ng/mL, IQR 592.4-1098.1; p<0.001], and than those with PTL without IAI who delivered at term (828.7 ng/mL, IQR 499.7-1119.6; p<0.001)). Among women with PTL without IAI, there was no difference in the median amniotic fluid concentration of RBP4 between those who delivered preterm and those who delivered at term (p=0.7). The black lines represent the median and IQR.