COVID-19 is not a causal risk for miscarriage: evidence from a Mendelian randomization study

Objective Coronavirus disease 2019 (COVID-19) has caused a global pandemic in the last three years. The lack of reliable evidence on the risk of miscarriage due to COVID-19 has become a concern for patients and obstetricians. We sought to identify rigorous evidence using two-sample Mendelian randomization (MR) analysis. Methods Seven single-nucleotide polymorphisms (SNPs) associated with COVID-19 were used as instrumental variables to explore causality by two-sample MR. The summary data of genetic variants were obtained from the Genome Wide Association Study (GWAS) among European populations in the UK Biobank and EBI database. Inverse variance weighting (IVW) method was taken as the gold standard for MR results, and other methods were taken as auxiliary. We also performed sensitivity analysis to evaluate the robustness of MR. Results The MR analysis showed there was no clear causal association between COVID-19 and miscarriage in the genetic prediction [OR 0.9981 (95% CI, 0.9872-1.0091), p = 0.7336]. Sensitivity analysis suggested that the MR results were robust [horizontal pleiotropy (MR-Egger, intercept = 0.0001592; se = 0.0023; p = 0.9480)]. Conclusions The evidence from MR does not support COVID-19 as a causal risk factor for miscarriage in European populations. The small probability of direct placental infection, as well as the inability to stratify the data may explain the results of MR. These findings can be informative for obstetricians when managing women in labor.