Maternity clothes wear sizing depends on your pre-pregnancy size, trimester, and how a dress stretches, not just your due date. In California's warm, layer-friendly climate, breathable fabrics and adjustable waistbands make it easier to get a comfortable fit from the first trimester through the third. Key Takeaways Buy one size up from your regular size if you're between sizes. Stretch-panel waistbands adapt best across all three trimesters. Maternity dresses for baby shower