['We aimed to study vaginal fluid phosphorylated insulin-like growth factor binding protein-1 (phIGFBP-1) testing in early pregnancy to predict spontaneous preterm delivery (PTD).', 'Vaginal and cervical swab samples were collected from 5180 unselected women during the first-trimester (mean gestational age 13.1\u2009weeks) ultrasound screening. PhIGFBP-1 was measured in vaginal and cervical fluid by an immunoenzymometric assay. Concentrations of ≥10\u2009µg/L were considered elevated. The outcome measure was spontaneous PTD at <32 or <37\u2009weeks gestation.', 'The median concentrations of first-trimester vaginal and cervical phIGFBP-1 were higher in women with spontaneous PTD at <32 and <37\u2009weeks gestation. When 10\u2009µg/L of phIGFBP-1 was used as a cut-off level, the OR in predicting PTD at <32\u2009weeks gestation was 8.6 (95% CI 3.6-20.7) for vaginal samples and 3.6 (95% CI 1.7-7.9) for cervical samples. At <37\u2009weeks gestation, the OR in predicting PTD was 3.0 (95% CI 1.9-3.9) for vaginal samples and 1.9 (95% CI 1.4-2.5) for cervical samples. In multiple logistic regression analysis, both elevated vaginal and cervical fluid phIGFBP-1 levels were independent predictors of PTD both at <32 and <37\u2009weeks gestation.'] Does early pregnancy vaginal fluid phosphorylated insulin-like growth factor binding protein-1 predict preterm delivery?