Cervical insulin-like growth factor binding protein-1 (IGFBP-1) to predict spontaneous onset of labor and induction to delivery interval in post-term pregnancy.

OBJECTIVE To evaluate whether insulin-like growth factor binding protein-1 (IGFBP-1) assessed in cervical secretion can predict successful induction and spontaneous onset of labor in post-term pregnancy, compared to ultrasound measurement of cervical length and Bishop score. DESIGN Cohort study, originating from a randomized controlled trial. SETTING Obstetric department of a university and tertiary referral hospital, Norway. POPULATION Five hundred and eight post-term women who had been randomized to induction of labor or expectant management 1 week beyond estimated day of delivery (289 [±2] days of gestation). METHODS Time to delivery was related to presence of IGFBP-1 in cervical secretion, Bishop score and ultrasound measurement of cervical length recorded at inclusion. MAIN OUTCOME MEASURES Spontaneous onset of labor and delivery within 3 days in the expectant management, and delivery within 24 hours of induction in the induction group. Test characteristics (sensitivity, specificity and negative and positive values and likelihood ratios) for IGFBP-1, Bishop score and cervical length were calculated. Logistic regression and Cox regression were used to account for parity and body mass index. RESULTS With expectant management, IGFBP-1 predicted spontaneous labor onset and delivery within 72 hours with low sensitivity and high specificity (0.45 and 0.80, respectively), as did Bishop score (0.24, 0.92). Cervical length was more sensitive (0.67, 0.58). IGFBP-1 predicted successful induction within 24 hours with low sensitivity and high specificity (0.30, 0.85), such as Bishop score (0.06, 1.00) and cervical length (0.45, 0.76). Parity enhanced successful induction. CONCLUSION IGFBP-1 predicts both spontaneous labor onset and successful induction in post-term pregnancy. Bishop score and cervical length performed equally well.