Registered report: Predictors and trajectories of physical activity before, during, and following twin pregnancy from the Norwegian Mother, Father and Child Cohort Study.

Many pregnant women do not meet guidelines for physical activity, and women with twin pregnancies are less likely to be physically active compared with singleton pregnancies. During and following pregnancy, physical activity patterns and their related predictors have not been previously explored in women pregnant with twins. Therefore, we aimed to examine stability and change in leisure-time physical activity (LTPA) from pre-pregnancy, during pregnancy, and up to 18 months after childbirth in women pregnant with twins and identify predictors of their LTPA patterns. This study was based on data from a nationwide, prospective cohort study, the Norwegian Mother, Father and Child Cohort Study (1999-2008), and the Medical Birth Registry of Norway. We used latent class growth analysis and logistic regression to identify patterns of LTPA and associated predictors among women pregnant with twins (n = 1,796). Two patterns were identified: low/moderate (53.3%) and high (46.7%). Parity, pre-pregnancy overweight and obesity, and primary education were associated with 36-60% lower odds of belonging to the high LTPA class compared to the low-to-moderate LTPA class. There is an urgent need to study the potential consequences of physical activity in twin pregnancies on maternal and fetal health.