Salivary progesterone as a biomarker for predicting preterm birth: A systematic review and meta‐analysis

Several biomarkers have been studied to predict spontaneous preterm birth, including salivary progesterone. However, due to limited studies, the utility of this biomarker remains controversial. This study synthesized the available literature and determined the role of salivary progesterone as a potential biomarker for preterm birth.All studies reporting the levels of salivary progesterone among pregnant women with reported birth outcomes were obtained from Ovid Medline, Scopus, CINAHL, and Cochrane Central Register of Controlled Trials from inception to January 10, 2022. A review of titles and abstracts was done independently by three reviewers. The quality of the studies was assessed using the Newcastle-Ottawa scale. Meta-analysis was performed in R v.4.1.3 using the "meta" package.Five studies involving 861 pregnant patients from Egypt, India, Iraq, and the US were included in this meta-analysis. The random-effects model showed that salivary progesterone level after the 28th week of gestation was significantly different between patients with term and preterm birth (standardized mean difference [SMD]: 1.99; 95% confidence interval [CI]: .44-3.54) with a high degree of heterogeneity (I2 = 96%, P < .001). Based on the results of this meta-analysis, women with term birth had higher level of salivary progesterone after the 28th week of gestation than those with preterm birth.In conclusion, the study results suggest that low salivary progesterone level after the 28th week of gestation is significantly associated with preterm birth. This study also highlights the use of saliva samples for monitoring sex steroid hormones throughout pregnancy.