Full length article The effect of blood staining on cervicovaginal quantitative fetal fibronectin concentration and prediction of spontaneous preterm birth $ Natasha L. Hezelgrave, Katy Kuhrt*, Kate Cottam, Paul T. Seed, Rachel M. Tribe, Andrew H. Shennan Division of Women's Health, King's College London, Women's Health Academic Centre, King’s Health Partners, St Thomas' Hospital, London, England, UK A R T I C L E I N F O Article history: Received 13 September 2016 Received in revised form 23 November 2016 Accepted 27 November 2016 Available online xxx Keywords: Blood staining Fetal fibronectin Preterm birth A B S T R A C T Objective: Spontaneous preterm birth is the leading cause of neonatal morbidity and mortality. Cervicovaginal fetal fibronectin (fFN) has enhanced prediction of preterm birth and, more recently, quantified results have become available so that management can planned more effectively and targeted to individual women. Manufacture guidelines stipulate that fetal fibronectin (fFN) samples should be discarded in the presence of moderate to heavy vaginal bleeding but there hasn’t yet been any formal investigation into the effect of blood staining on fetal fibronectin concentration and subsequent preterm birth prediction. The objective for this study was to determine the impact of blood stained swabs on quantitative fetal fibronectin (qfFN) concentration and prediction of spontaneous preterm birth (sPTB) in asymptomatic high-risk women. Study design: Predefined blinded sub-analysis of a larger prospective study of qfFN in asymptomatic women at high-risk of preterm labour. Women with and without blood stained swabs were matched for gestational age at testing and delivery, risk factors and cervical length measurement. Results: Median fFN concentration in blood stained swabs (n = 58) was 66 ng/ml vs. 7.5 ng/ml in the controls (n = 58) (p < 0.0001). At 50 ng/ml threshold the false positive ratio (FPR) in blood stained was 25/33 (75.8%) vs. 8/15 (53%) in controls, (risk difference 22.4; 6.8 to 51.6, p = 0.18). At 50 ng/ml threshold the false-negative ratio (FNR) in blood stained was 2/25 (8.0%) vs. 1/43 (2.3%) in controls (risk difference 5.7; 17.2 to 5.9, p = 0.55). At each threshold 10, 50 and 200 ng/ml blood stained swabs had higher sensitivity but lower specificity for predicting preterm birth. Receiver Operating Characteristic (ROC) curve, the strongest global measure of test performance, for prediction of delivery at <34 weeks gestation was similar in blood stained vs. control groups. (0.78 vs. 0.84) in blood stained vs. control groups respectively. Conclusion: Blood stained swabs have elevated qfFN concentrations but may still have predictive value, and clinical utility. Very low fFN values (<10 ng/ml) are especially reassuring and indicate lower risk of delivery than non-blood stained swabs. The higher false positive rate must be noted and explained to the patient. © 2016 Published by Elsevier Ireland Ltd. Introduction Spontaneous preterm birth (sPTB), birth before 37 completed weeks’ of gestation), is the leading cause of neonatal morbidity and mortality [1]. Prediction of sPTB in symptomatic and asymptom- atic high-risk women has been enhanced in recent years by the use of cervicovaginal fluid (CVF) fetal fibronectin (fFN) testing, now widely used in clinical practice. fFN is a glycoprotein found at the interface between chorion and decidua [2] which is usually present in low levels in CVF from 18 weeks of gestation; high levels after $ Natasha L. Hezelgrave is funded by a National Institute for Health Research (NIHR) Doctoral Research Fellowship (DRF-2013-06-171). The views expressed are those of the authors and not necessarily those of Tommy's, the NHS, the NIHR or the Department of Health. * Corresponding author. E-mail address: katykuhrt24@gmail.com (K. Kuhrt). http://dx.doi.org/10.1016/j.ejogrb.2016.11.027 0301-2115/© 2016 Published by Elsevier Ireland Ltd. European Journal of Obstetrics & Gynecology and Reproductive Biology 208 (2017) 103–108 Contents lists available at ScienceDirect European Journal of Obstetrics & Gynecology and Reproductive Biology journal homepage: www.elsevier.com/locate/ejogrb