For maternity clothing the sizing is typically arranged as a normal UK size eg. 6, 8, 10, 12, 14, 16 and then sometimes broken down further by trimester or month of pregnancy. The base pattern is typically aimed at a woman in the second to third trimester as normal clothing can fit some women for the first trimester. Trousers are sized using a waist size eg. 26, 28, 30, 32 and remains the same waist size as the woman would wear pre-pregnancy but accounts for extra growth in the stomach and additional areas in the base size pattern.
Bespoke grading is specifically useful in this market as woman’s bodies can change in different parts during pregnancy, so targeting a specific niche could be particularly profitable if done successfully.