"In the existing body of literature, exercise during pregnancy has generally not been associated with miscarriage,17–19 and one case–control study has even reported a protective effect of exercise during pregnancy.20 In contrast, Hjollund et al.21 found an increased risk of early miscarriage among women who reported a high physical strain around the time of implantation of the embryo. Furthermore, lay people have tried to use excessive physical exercise as an abortifacient, and older literature mentions physical activity (e.g. jumping, running, and horseback riding) as a cause of miscarriage. Considering the relatively sparse literature and the somewhat inconsistent results, we wanted to examine the association between exercise during pregnancy and miscarriage in a large population-based cohort."