Can fetal fibronectin testing and cervical length measurement direct appropriate prophylactic steroid use in high-risk, asymptomatic women?

Abstract

Introduction Antenatal corticosteroids to accelerate fetal lung maturation should be administered to women 24 to 34 weeks gestation with any symptoms of imminent delivery,1 with proven benefit up to 2 weeks and possibly 4 weeks after administration. There is concern as to potential harm caused by premature administration or repeated doses.23 Could fetal fibronectin (fFN) testing and ultrasound cervical length (CL) measurement, excellent predictors of preterm birth (PTB), be used to direct steroid administration in high-risk, asymptomatic women? Method Prospective analysis of 284 high-risk asymptomatic women between 22+0 and 32+6 weeks gestation, seen in preterm clinic. Results <1%(CI 0.1 to 3%) of fFN negative women delivered ≤4 weeks of testing, despite CL<25 mm in 43 of these women. 5% (CI 0.1 to 26%), 25%(CI 5 to 57%) and 38% (CI 17 to 64%) of women with positive fFN and CL≤25 mm, 15 to 25 mm and ≤15 mm respectively delivered ≤4 weeks of testing. 33% (CI 13 to 59%) of those with positive fFN and CL≤15 mm delivered prematurely, but >4 weeks from testing, as did 58%(CI 31 to 80%) and 21%(CI 6 to 45%) of fFN positive with CL 15 to 25 mm and ≤25 mm. Conclusions fFN has the potential to prevent the inappropriate use of steroids in screen-negative high-risk women, despite CL. CL adds additional value in screen-positive women. Although 38% of fFN positive and CL<15 mm women delivered within 4 weeks (27% ≤2 weeks), that 33% of these had PTB outside of this steroid window implies that repeat doses may have been necessary. fFN and CL can inform steroid administration, but repeat testing will be required, and further research must establish the risk/benefit of these management strategies.

The Role of PTB Clinics: A Review of the Screening Methods, Interventions and Evidence for Preterm Birth Surveillance Clinics for High-Risk Asymptomatic Women

“…In one observational study of high-risk asymptomatic women, < 1% (95% CI 0.1% -3%) of fFN negative women delivered within a month of testing, despite having a cervix < 25 mm (46). Consequently, a negative fFN value is reassuring and can prevent unnecessary intervention despite shortening cervical length.…”

“…Consequently, a negative fFN value is reassuring and can prevent unnecessary intervention despite shortening cervical length. When a short cervix (< 25 mm) was combined with a positive fFN value, 21% (95% CI 6% -45%) of women delivered prematurely (46). Therefore, combining predictive tests allows clinicians to re-classify women according to their risk and avoid prescribing interventions in patients who don't actually need them.…”

“…Cerclage is indicated in cases of recurrent PTB, and short and/or dilated cervix (45,46). The mechanisms by which stitches prevent PTB is unclear, but they may provide support to a weak cervix, maintain length and/or strengthen the endocervical mucus plug against ascending infections (56,57).…”