Postpartum weight retention is associated with an increased risk of obesity later in life, as well as chronic diseases such as cardiovascular diseases, hypertension, and cancer. Postpartum weight retention is also linked to influencing the health of the child, such as breastfeeding and children's gut microbiome. Our study found that higher habitual levels of physical activity, instead of the change of physical activity across 8 weeks, may be associated with postpartum weight change. Our research has the potential to inform important interventions that can support women during pregnancy and postpartum, as well as the health of their children. We hope that our findings can help encourage physical activity and healthy weight loss during this crucial period of life, leading to improved overall well-being for both mother and child, as well as a strong culture of healthy living for the entire family.