First of all, I want to tell you here that whether pregnant women can go out in shorts depends mainly on the type they choose. If you choose to wear bottoming shorts in spring and autumn or winter, you can't wear them outside. If you choose summer, there are some people who can wear it outside and some who can't. Therefore, it is mainly based on the type you choose to judge whether the leggings for pregnant women can be worn outside.
It is actually relatively simple to change ordinary leggings into maternity pants. However, whether you can change into maternity pants depends on your body shape. Although many leggings are more elastic now, if you are fat or edema during pregnancy, there is no way to change ordinary leggings into maternity pants.
However, if your figure is still slim, it is relatively simple to change leggings into maternity pants, just modify the waist. Take a piece of elastic cloth with the same color as leggings, wrap it around your stomach for half a circle, take out a piece of cloth with the right size, then cut off the front half of the waist of ordinary leggings, and sew the trimmed cloth on it, so that ordinary leggings can be converted into maternity pants.