Rat had 7 babies and 6 died why??

Question
My female rat got out of her cage when my boys were out about 23 days ago and when I came in they were mating. Anyways I realized she was pregnant about 1 1/2 weeks ago. I put her in an aquarium and provided her with everything pregnant rats need. Anyways about 3 days ago she started bleeding a little. She bled a few spots on friday, a few on saturday, and a sunday(today) she had 6 dead babies and one little guy managed to stay alive. I removed the dead babies and she is doing great the one baby left. She is a great momma. Anyways I was wondering if you know why the babies died?? And do you think the last baby is gonna make it? Is there anything I can do to ensure it survives? Thanks

Answer
Sorry this took so long to answer. It was floating in limbo and not sent to any expert in particular.

I am sorry for the loss of the babies. It is impossible to know why the babies died but there are many factors. The fact one is alive and still thriving well means the mother indeed is lactating and nursing but you need to be sure. Turn the pup over and check his belly. The skin is transparent and you will see the belly containing mothers milk. We refer to it as milk band. If you see that, you know the baby is getting fed properly. Also, the mother needs to stimulate the babies to urinate and defecate and if that isn't being done, toxins back up and the pups die. Again though, if there is one survivor, that means something may have gone wrong with the development of the other 6 and the 7th is a miracle pup!!

I think I read your post wrong though and am I to understand that the 6 were born still born? If thats the case, again, there is alot that can go wrong, especially birth trauma.

How are things now?