Introduction: Vitamin D binding protein (VDBP) has been previously identified in amniotic fluid and the cervicovaginal fluid (CVF) of pregnant women. Proteomic analysis of CVF has also reported increased VDBP in women who experience spontaneous preterm birth.1 The biological functions of VDBP include acting as a carrier protein for vitamin D metabolites, the clearance of actin monomers released during tissue injury and the augmentation of the inflammatory immune response. It is hypothesised that the concentration of VDBP will be altered in the CVF of women approaching parturition.
Aim: To determine: (i) the relationship between VDBP in the CVF concentration in asymptomatic women with impending spontaneous term labour and (ii) the utility of VDBP to predict labour within 3 days of onset.
Methods: Serial CVF samples were collected weekly from 67 healthy women with a singleton pregnancy at 36 weeks’ gestation until labour onset. VDBP was measured by ELISA. Binary logistic regression analysis was performed on 43 women using two samples collected at 3-4 weeks and up to 1 week before labour onset.
Results: VDBP concentration was 2.2 to 16.9-fold significantly increased in labour compared samples collected at 4-7, 8-14, 15-21, 22-28 and ≥29 days before labour (n=176 samples; p<0.05). VDBP measured at 0-3 days was significantly increased 2.8 to 7.9-fold compared to 8-14, 15-21, 22-28 and ≥29 days before labour (p<0.05). VDBP was significantly increased with advancing gestation (p<0.001). The predictive efficacy of VDBP to predict spontaneous term labour onset within 3 days provided a sensitivity and specificity of 98.6% and 93.8% (ROC curve area=0.988; 95% CI=0.970-1.000; p<0.01).
Conclusion: This longitudinal study of asymptomatic women suggests that VDBP in the CVF may be a useful predictor of labour. Studies are currently in progress to evaluate the efficacy of VDBP to predict spontaneous preterm birth.