I bought a pair of pants and a pair of jeans on clearance towards the end of my pregnancy. I thought I could wear them for post-partum and then future pregnancies. Unfortunately, they were really big and never fit right. I thought the elastic was broken on the one pair and that the other pair was for the third trimester. Then I bought these jeans for my son:
They have an adjustable elastic that you can pull and button. They even have an extender elastic to make them bigger, though I doubt we'll ever need that with Ian's body type.
I pulled out my maternity clothes and looked at the pants and jeans and realized they were designed the same way. I didn't realize it because they elastic was totally retracted in the pants and there were no internal buttons, they must have broken off. On the jeans, the elastic was sticking out of one side only and I thought it had broken.
More than two years later, I finally figure it out. I pulled out the elastic and rethreaded it through with a safety pin on the jeans and did the same on the pants as well as added two buttons. So now I have two pairs of jeans and one pair of pants.