Introduction Low saliva progesterone concentrations are associated with spontaneous preterm birth (SPTB) in high risk women.¹ This study further evaluated the combined use of fetal fibronectin (fFN) and saliva progesterone for SPTB prediction.

Methods A predefined secondary analysis undertaken on a subgroup of women from a prospective cohort (n = 1216) of asymptomatic women at high risk of SPTB. Participants provided at least one saliva sample between 20⁺⁰ and 28⁺⁶ weeks’ and some underwent a qualitative fFN test (Hologic™; positive test results ≥50 ng/ml). Saliva progesterone concentrations were measured by ELISA (Salimetrics™). Primary end point was SPTB or rupture of membranes with delivery before 34 weeks’. Exclusions: women with iatrogenic PTB before 34 weeks’ and women on progesterone supplementation or in the OPPTIMUM trial.

Results Overall, 638 women with paired saliva progesterone and fFN results (22⁺⁰ and 25⁺⁶ weeks’) were identified with a SPTB rate <34 weeks’ of 4.5%. A saliva progesterone concentration of <280 ng/l was associated with an odds ratio for delivery <34 weeks’ of 3.81 (95% CI: 1.34 to 10.83); for fFN, the receiver operating characteristic curve (ROC) area for SPTB <34 weeks’ was 0.61 (0.53 to 0.70). Combination of tests improved the ROC area [0.67 (0.56 to 0.78)]. In fFN negative women (n = 583), low saliva progesterone concentrations were associated with greater risk of SPTB <34 weeks’ [positive likelihood ratio 3.4 (1.34 to 8.71)].

Conclusions Saliva progesterone measurement may be useful for prediction of SPTB in high risk women as an adjunct to fFN testing.

Reference

1. Lachelin GCL, et al. BJOG 2009;116:1515–9