Physical activity during pregnancy: key beliefs to support intervention

Physical activity (PA) provides maternal and fetal health benefits, but only 27.5% of Canadian pregnant women meet PA recommendations. Theory-based interventions like the theory of planned behavior (TPB) are useful in explaining what drives behavior. The first objective of this study was to validate the TPB model to predict prenatal moderate-to-vigorous physical activity (MVPA), including testing of the novel interaction between intention and perceived behavioral control (PBC). The second objective was to identify which specific beliefs predict intention toward prenatal MVPA to support intervention.

We used a prospective correlational design. Healthy pregnant women completed two electronic questionnaires: at baseline, to assess TPB constructs, and one month later, to assess MVPA practice. Structural equation modeling was conducted with Latent Moderated Structural Equations. The interaction was interpreted with the pick-a-point method and the Johnson-Neyman graphical method.

The sample consists of 193 women (M _age = 31.2±3.6). Results indicate that prenatal MVPA at one month was marginally predicted by intention (β = 0.149; p < 0.10) and PBC (β = 0.322; p < 0.05, MVPA R ²= 20%), but when their interaction was added to the model, MVPA R ² increased to 44%. Specifically, the relationship between intention and MVPA is stronger when PBC is high (0.5 standard deviation over the mean). In the full model including the interaction, attitude (β = 0.59; p < 0.001), subjective norm (β = 0.20; p < 0.01) and PBC (β = 0.26; p < 0.05) all made a significant contribution to predicting MVPA intention (R ²= 88%). Finally, the following beliefs displayed significant indirect paths toward the intention of being physically active: behavioral beliefs: unlikely to be more tired and likely feel better mentally; normative beliefs: approval from friends and from mother/father; and control beliefs: being tired and missing social support.

Interventions aiming to promote regular MVPA during pregnancy should prioritized the six significant beliefs identified to significantly predict intention toward prenatal MVPA.