Association between increased antenatal vaginal pH and preterm birth rate: a systematic review

Objective:

Worldwide, 14.9 million infants (11%) are born preterm (PTB) each year. Up to 40% of PTB are associated with genital tract infections. The vaginal pH can reflect changes in the vaginal milieu and, if elevated, indicates an abnormal flora or infection. The aim of this study is to investigate, whether an increased antenatal vaginal pH > 4.5 in pre-labour pregnant women is associated with an increased preterm birth rate < 37 completed weeks gestation.

Methods:

Databases included SCOPUS, EMBASE, MEDLINE, PsycInfo and the Cochrane Central Register of Controlled Trials, complemented by hand search, up to January 2017. Selection criteria were primary research reporting vaginal pH assessment in pre-labour pregnant women and preterm birth rate. Data extraction and appraisal were carried out in a pre-defined standardised manner, applying the Newcastle-Ottawa Scale and Cochrane Risk of Bias tool. Analysis included calculation of risk difference (RD) and narrative synthesis. It was decided to abstain from pooling of the studies due to missing information in important moderators.

Results:

Of 986 identified records, 30 were included in the systematic review. Risk of bias was considered mostly high (40%) or moderate (37%). Fifteen studies permitted a calculation of RD. Of these, fourteen (93%) indicated a positive association between increased antenatal vaginal pH and PTB (RD range: 0.02 – 0.75).

Conclusions:

An increased antenatal vaginal pH > 4.5 may be associated with a higher risk for preterm birth. It is recommended to conduct an RCT to investigate the effectiveness of antenatal pH to prevent PTB.