Self-testing of vaginal pH to prevent preterm delivery: a controlled trial.

Background: From 2004 to 2006, in a model project carried out by four German health insurers, expectant mothers were offered self-testing of vaginal pH in order to prevent preterm delivery. They were given pH test gloves on request so that they could measure their vaginal pH twice a week from the 12(th) to the 32(nd) week of gestation. They were instructed to consult with a gynecologist after any positive result. All further diagnostic or therapeutic decisions were at the discretion of the treating gynecologist. We assessed the effectiveness of the screening intervention, using delivery before the 37th week of gestation as the primary endpoint.

Methods: In this prospective, controlled trial, we collected data on deliveries from 2004 to 2006 that were covered by the four participating insurers in five German federal states. We compared the outcomes of pregnancy in women who did and did not request test gloves (intervention group, [IG], and control group, [CG]). The data were derived from claims data of the participating insurers, as well as from a nationwide quality assurance auditing program for obstetrics and perinatal care. Propensity score matching and multivariate adjustment were used to control for the expected self-selection bias.

Results: The study sample comprised 149 082 deliveries. 13% of the expectant mothers requested test gloves, about half of them up to the 16(th) week of gestation. As expected, women with an elevated risk of preterm birth requested test gloves more often. Delivery before the 37(th) week of gestation was slightly more common in the intervention group than in the control group (IG 7.97%, CG 7.52%, relative risk 1.06, 95% confidence interval 1.00-1.12). This result was of borderline statistical significance in the propensity score matched analysis, but it was not statistically significant in the multivariate model.

Conclusion: This trial did not demonstrate the efficacy of self-testing of vaginal pH for the prevention of preterm delivery (< 37 weeks of gestation).