In logistic regression analysis controlling for FFN , cervical length , prior preterm birth , and treatment group , positive FFN was significantly associated with birth < @ and < @ weeks ( odds ratio @ -LSB- @ % confidence interval @-@ -RSB- , @ -LSB- @-@ -RSB- , respectively , p < @ for both ) but cervical length @ mm was not ( odds ratio @ -LSB- @-@ @ -RSB- , @ -LSB- @-@ @ -RSB- ) .