RESULTS	Positive fetal fibronectin assays at 28 weeks but not at 20-24 weeks were associated with lower mean birthweight ( 199 g , P < .001 ) ; lower mean gestational age ( 2 weeks , P < .001 ) ; six-fold higher rate of preterm birth less than 32 weeks ( 10.8 % compared with 1.9 % , odds ratio 6.3 , 95 % confidence interval 3.2-12 .3 ) and a two-fold higher rate of preterm birth less than 37 weeks ( 38.7 compared with 22.0 % , odds ratio 2.3 , 95 % confidence interval 1.5-3 .3 ) .\