evidence: One question of particular interest was the risk of miscarriage following COVID-19 vaccination in early pregnancy. This is particularly important as up to 40% of pregnancies are unintended and may go unrecognised until 4–8 weeks’ gestation or beyond, so that inadvertent vaccination in early pregnancy is likely to be common41. The mRNA vaccine causes both antibody and cellular immune responses; given the importance of T-cell suppression in placental development and fetal wellbeing42, concern has been expressed that the vaccine may increase miscarriage risk. Social media has been full of reports that have fuelled this concern, and many pregnant people have cited this fear as their primary reason for vaccine hesitancy. Our data do not support such concerns, based on both observational data13,19,24,26,27,29 (even when accounting for potential time-varying confounding27,29) and inadvertent exposure in early pregnancy in vaccine trial participants1,2,35,36,37. Our finding of a lower incidence of stillbirths in the vaccinated cohort is important, given that COVID-19 in pregnancy is associated with an increased risk of stillbirth, particularly in the period of Delta dominance43. A recent report of population-level data from Scotland found that following SARS-CoV-2 infection in unvaccinated pregnant people, the perinatal death rate was 22.6 per 1000 births, while in contrast, no vaccinated pregnant people with breakthrough infection suffered a perinatal death44. Taken together with our findings, these data point to the severity of COVID-19 as the mediator of the COVID-19 and stillbirth relationship. However, the observational nature of the original studies, significant statistical heterogeneity observed in the results and other probable confounders should caution not interpret these results as causal.