Objective
reduction of physical activity (PA) during pregnancy is common but undesirable, as it is associated with negative outcomes, including excessive gestational weight gain. Our objective was to explore changes in five types of activity that occurred during pregnancy and the behavioural determinants of the reported changes in PA.

Design
we performed a secondary analysis of a cross sectional survey that was constructed using the ASE-Model – an approach to identifying the factors that drive behaviour change that focuses on Attitude, Social influence, and self-Efficacy.

Participants
455 healthy pregnant women of all gestational ages, receiving prenatal care from midwifery practices in the Netherlands.

Findings
more than half of our respondents reported a reduction in their PA during pregnancy. The largest reduction occurred in sports and brief rigorous activities, but other types of PA were reduced as well. Reduction of PA was more likely in women who considered themselves as active before pregnancy, women who experienced pregnancy-related barriers, women who were advised to reduce their PA, and multiparous women. Fewer than 5% increased their PA. Motivation to engage in PA was positively associated with enjoying PA.

Key conclusions and implications for practice
all pregnant women should be informed about the positive effects of staying active and should be encouraged to engage in, or to continue, moderately intensive activities like walking, biking or swimming. Our findings concerning the predictors of PA reduction can be used to develop an evidence-based intervention aimed at encouraging healthy PA during pregnancy.