Fetal fibronectin, interleukin-6, and C-reactive protein are useful in establishing prognostic subcategories of idiopathic preterm labor

OBJECTIVE: Our purpose was to evaluate fetal fibronectin, interleukin-6, and C-reactive protein from patients with preterm labor to establish prognostic subcategories. STUDY DESIGN: Thirty-seven patients with preterm labor had cervical fetal fibronectin and plasma C-reactive protein sampled. Eighteen of these patients had amniotic fluid interleukin-6 levels measured. Outcome variables were (1) delivery before 34 week and (2) delivery within 48 hours. RESULTS: Detectable cervical fetal fibronectin identified 89% of patients who were delivered before 34 weeksʹ gestation. Interleukin-6>1500 pg/ml identified 88% of patients who were delivered within 48 hours. C-reactive protein>1.5 mg/dl correlated with elevated interleukin-6 levels (p< 0.001). CONCLUSIONS: Three subcategories of idiopathic preterm labor were evident: (1) fetal fibronectin nondetectable (37% likely to be delivered before 34 weeks), (2) fetal fibronectin detectable but interleukin-6 <1500 pg/ml (79% likely to be delivered before 34 weeks but 85% with>48 hoursʹ latency), and (3) fetal fibronectin present and interleukin-6>1500 pg/ml (91% likely to be delivered with <48 hoursʹ latency).