Pregnant females bedding?

I started a mouse colony about 2-3 weeks ago and I have 2 visibly pregnant girls (whose to say the others arent and just arent showing). Those 2 are in a tub to themselves now. I use pine pellets, should I be changing them to regular pine or aspen bedding for them to nest in? I search a little on the forums and got mixed results. Any ideas?

I just add aspen to 1/4 of the cage and some egg cartons for them to shred, shredded paper if I have any around.

Keep them on pellets and add some wood shaving for nesting material.

Ok thx, I guess that explains why they are tearing up the toilet paper tubes I been putting in.

Yep, I keep mine on the pellet bedding and add extra aspen and toilet paper rolls for them to shred.

I keep mine on the pellets and usually give shredded newspaper for them to make a nest. I tried not giving them any nesting material for a while, and they ended up piling up ALL the pellets in a corner to make their nest, then peeing and pooping in a different corner where there was no substrate. That was major yuck, so they always get something to build a nest out of now.