This study contributes to the limited body of research on weight trajectories and lifestyle behaviors in women during the transition from pre- to post-pregnancy. The analysis included 26 women from the Guelph Family Health Study who became pregnant during their participation. The participants were categorized into weight gain, weight maintenance, and weight loss groups, although no participants fell into the weight loss category. Weight measurements, energy, macronutrient intake, and physical activity levels were assessed using independent t-tests and weight trajectories were depicted through line graphs for each group. Weight measurements were obtained through in-person assessments or self-assessment, while dietary intake was evaluated using self-reported 24-hour recall and physical activity was measured using the IPAQ short version. All participants provided a minimum of one pre- and post-pregnancy weight measurement, along with one or more physical activity or dietary intake assessment results. The findings revealed that compared to women who maintained their weight, those who experienced weight gain were significantly more physically active post-pregnancy and had a significantly higher increase in fat intake pre- to post-pregnancy. This study highlights the importance of further research to investigate weight trajectories in pregnant women, with a particular focus on understanding the long-term impact of diet and physical activity behaviors on postnatal weight trajectories.