What to compare in a maternity dress
Most of the difference between maternity dresses comes down to where the extra room sits. Wrap and empire styles release fabric from just under the bust, which usually keeps working across a growing bump and afterwards. Ruched side seams stretch and then relax, so the same dress reads differently in the second and third trimester. Bodycon jersey shows the bump earlier and tends to fit for a shorter stretch of the pregnancy.
Fabric decides how the dress behaves more than the silhouette does. Heavier jersey and ponte hold their shape over a bump; light viscose and satin drape but cling more. If you want the dress after birth as well, check whether it has nursing access — many maternity dresses do not, and the listings here show when a brand describes both uses.
Sizing is usually your pre-pregnancy size, because the pattern already allows for the bump. Length is the exception worth checking: a maxi that fits at 20 weeks can sit shorter at 36 weeks as the hem rises over the bump. Each brand publishes its own measurements in its store.