Fetal Fibronectin versus Cervical Length as Predictors of Preterm Birth in Twin Pregnancy with or without 17-Hydroxyprogesterone Caproate

Objective The objective of this study was to compare cervicovaginal fetal fibronectin (FFN) versus transvaginal sonographic cervical length as predictors of preterm birth in twin pregnancy and to test whether 17-hydroxyprogesterone caproate (170HPc) modifies the predictive value of FFN. Study Design Secondary analysis of a randomized trial of 170HPc versus placebo in dichorionic-diamniotic twins, analyzing the subset with screening FFN (N = 198) and/or cervical length (N = 214) at 24 to 26 weeks of gestation. Results Positive FFN was found in 7%, cervical length <= 25 mm in 8%, and both positive FFN and cervical length <= 25 mm in 3%. Birth <32, <34, and <37 weeks occurred in 8, 30, and 67%, respectively. In logistic regression analysis controlling for FFN, cervical length, prior preterm birth, and treatment group, positive FFN was significantly associated with birth <30 and <32 weeks (odds ratio 55.0 [95% confidence interval 5.2-582], 18.1 [3.3 99], respectively, p < 0.001 for both) but cervical length <= 25 mm was not (odds ratio 0.1 [0.002-1.6], 0.6 [0.1-4.3]). Conclusion Positive FFN was stronger than cervical length <= 25 mm in predicting early preterm birth in twins, regardless of 170HPc use. Treatment with 170H Pc did not appear to alter the predictive value of FFN.