ok I just did a search and I found this

it is important that you leave the dad in with mom to help her raise the babies. Otherwise the experience will be stressful for the mother gerbil and she may not be able to handle it on her own – especially a firstime or older mom. If you do split a breeding pair, leave a daughter from the last litter to help mom raise the pups.
here is the page I got it from, read all of it, it looks very helpfull
gerbi breeding help