Seminal oxidative stress and recurrent pregnancy loss: a systematic review and meta-analysis

Recurrent pregnancy loss (RPL) affects up to 2% of couples. This systematic review and meta-analysis synthesized the evidence on the relationship between seminal oxidative stress and RPL. This study aimed to evaluate whether seminal oxidative stress markers differ between men from couples experiencing RPL and those from fertile control couples. This study adhered to the Preferred Report Items for Systematic Review and Meta-analysis and Meta-analysis of Observational Studies in Epidemiology guidelines. PubMed, EMBASE and Web of Science were searched. The quality of the included studies was assessed using the Newcastle-Ottawa Scale. Meta-analysis using Review Manager computed pooled estimates of standardized mean difference (SMD) for various oxidative stress markers. Seven studies were included (seven in the systematic review and six in the meta-analysis) comprising 243 and 216 men in the RPL and control groups, respectively. Pro-oxidant marker concentrations were elevated significantly in men in the RPL group compared with the control group (SMD = 1.59, 95% CI 1.30-1.89, P < 0.00001, fixed-effects model; SMD = 1.80, 95% CI 0.04-3.55, P = 0.04, random-effects model). The RPL group had significantly reduced antioxidant markers (SMD = -1.04, 95% CI -1.32 to -0.75, P < 0.00001, fixed-effects model; SMD = -1.46, 95% CI -2.39 to -0.52, P = 0.002, random-effects model). The findings suggest that seminal oxidative stress is significantly associated with RPL.