Detection of fetal fibronectin as a predictor of preterm delivery in high risk asymptomatic pregnancies

Authors


Correspondence: Dr S. C. Leeson, Department of Obstetrics and Gynaecology, Saint Mary's Hospital, Hathersage Road, Manchester M13 9PT, UK.

Abstract

Objective The study was designed to determine whether fetal fibronectin would predict delivery before 37 weeks in women at high risk of preterm delivery.

Study methods Forty-three women considered at risk of preterm delivery were recruited antenatally into a blind longitudinal study. Quantitative assays of fetal fibronectin were obtained from sequential high vaginal swabs taken fortnightly from 24 to 34 weeks of gestation. Fibronectin concentrations of 0.05 μg/ml or more were considered as positive.

Results Results were calculated by swab and by subject. The sensitivity of an individual fibronectin swab in predicting preterm delivery within 14 days of testing was 71% and the specificity was 93Yo. The overall positive predictive value was 31% and the negative predictive value was 99%. The sensitivity of the fibronectin swab in predicting delivery before 37 weeks was 17% and the specificity was 93 Oh. The positive predictive value was 50% and the negative predictive value was 73%. For a woman who has had a positive swab the sensitivity in predicting preterm delivery within 14 days of testing was 80% and the specificity was 83 %; a woman was counted as positive only if the final swab was positive and preceded delivery by not more than 14 days. The positive predictive value was 36% and the negative predictive value was 97%. For a woman who has had a positive swab the sensitivity in predicting delivery before 37 weeks was 54%. The specificity, the positive predictive value and the negative predictive value were 85%, 64% and 79%, respectively. Women were counted as positive if any swab in the sampling sequence was positive. Fibronectin swabbing when calculated by patient did predict preterm delivery within 14 days of testing (P= 0.01) and before 37 weeks (P= 0.01). Analysis of the accuracy of predicting delivery from 7 to 28 days after sampling revealed that the best prediction for delivery was within the following 14 days.

Conclusion Serial fetal fibronectin assessment from 24 to 34 weeks of gestation anticipated preterm delivery within 14 days of testing and before 37 weeks for high risk asymptomatic women. Such testing should be performed every two weeks.

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