Prediction of spontaneous preterm birth using quantitative fetal fibronectin after recent sexual intercourse.

Objective: The purpose of this study was to determine the effect of sexual intercourse on the accuracy of quantitative fetal fibronectin (qfFN) in the prediction of spontaneous preterm birth (sPTB) in asymptomatic high-risk women.

Study Design: This was a prospective masked predefined subanalysis of a larger study of cervicovaginal fluid qfFN concentration in high-risk women asymptomatic of preterm labor. Women who had sexual intercourse within 48 hours of qfFN testing (n = 61; 18(+0)-34(+6) weeks' gestation) were compared with controls from the same database without a history of pretest sexual intercourse, matched according to gestational age at testing and delivery, risk factor for sPTB, and ultrasonographic cervical length measurement.

Results: The median concentration of qfFN in women who had sexual intercourse within 48 hours of testing was 53 ng/mL (quartiles 6, 189), compared with 5 ng/mL (quartiles 2, 12) in the control group. The average qfFN concentration was 6.36 (95% confidence interval [CI], 3.43-11.8) times higher in the sexual intercourse group compared with controls (P < .0001). The false-positive rate was 56% (27 of 50) compared with 6% (3 of 52) in the control group (risk difference, 48%; 95% CI, 33-63; P < .001). The false-negative rate was 45% (5 of 11) vs 89% (8 of 9) in the control group (risk difference, -43%; 95% CI, -79 to -8; P = .043).

Conclusion: Sexual intercourse within 48 hours of testing is associated with increased levels of fetal fibronectin in vaginal secretions and an increased rate of false-positive results in the prediction of sPTB in asymptomatic women.