Investigating the effects of maternal physical activity on pregnancy and perinatal outcomes: an integration of multiple lines of evidence

The experience of pregnancy is accompanied by a range of physiological and psychological changes that may contribute to reduced physical activity and increased sedentary behaviour. Historically, physical activity during pregnancy was viewed with caution, particularly due to concerns that it might increase the risk of miscarriage. However, this perception may be driven by reverse causality: individuals in the early stages of an unrecognised miscarriage may experience fewer typical symptoms—such as nausea or fatigue—and may therefore feel well enough to remain physically active. Such concerns may have led healthcare professionals to promote rest and sedentary behaviour out of caution.
Emerging evidence from epidemiological studies suggests that maintaining higher levels of physical activity and reducing sedentary time during pregnancy are associated with improved maternal and offspring health outcomes. As a result, several national guidelines now promote physical activity during pregnancy as both safe and beneficial.
Despite this, questions remain about whether these associations reflect true causal relationships. Conventional statistical approaches, such as multivariable regression, can be affected by confounding factors and reverse causation, limiting causal inference. To address these limitations, this study adopts a triangulation approach that combines multivariable regression, Mendelian randomisation (MR), and paternal negative control designs.
By integrating these complementary methods, this research aims to provide more robust evidence on the potential causal effects of physical activity during pregnancy on a range of pregnancy and perinatal outcomes.