These leggings are made especially for the growing belly. The connection of the pants with the waistband starts in the front very low so that your growing belly will be above the stitching. In the back, the connection is higher, above your buttocks.
And after your pregnancy, they'll go back to hugging your old body again so you'll be able to enjoy them still after your delivery.
Our pregnant friend was so sweet to make some photos and she's wearing it with our crinkle sports bra in size M/L: