Prediction of spontaneous preterm birth using fetal fibronectin in women with a low-lying placenta

OBJECTIVE: To determine the effect of a low lying placenta on the concentration of quantitative fetal fibronectin (qfFN) in the cervicovaginal fluid (CVF), and predictive accuracy for spontaneous preterm birth in asymptomatic high-risk women (18(+0)-24(+0) weeks gestation).

METHODS: Median concentrations of qfFN were compared in women who had a low lying placenta, covering the cervical os (n = 61) to matched controls (n= 61) without a low lying placenta. Proportions of women with raised qfFN concentrations (>10ng/ml), and false positive and negative rates (FPR and FNR) for spontaneous preterm delivery were also compared.

RESULTS: The median concentration of qfFN in women with low lying placenta was 5.0 ng/mL, compared with 6.0 ng/mL in controls. Proportion of women with raised levels (>10 ng/mL), positive levels (>50ng/mL) and very high levels (>200ng/mL) were similar in both groups (62.3% vs 59.0%, 16.3% vs 22.0% and 6.5% vs 4.9%, p > 0.05 for all thresholds). The FPR and FNR rate for delivery before 34 and 37 weeks were also comparable (FPR 90.0% vs 85.7% and 80.0% vs 78.6%; FNR 5.8% vs 4.3% and 9.8% vs 8.5%) Conclusions: CVF qfFN concentrations in asymptomatic high-risk women are not affected by the presence of a low-lying placenta.