female rat just had 13 babies in the last 2hrs

I had a momma rat who had 18 babies once. All the babies were fine. I just took the bigger ones out a few times a day so the smaller ones could get some one on one time with momma :)

I have had one litter of 19 and multiple litters of 17 babies that all not only survived but thrived.
I've had first time moms drop 15 babies which is fairly uncommon, I average more like 10 for first litters and then I usually get 12-15 for several more litters before they slow down to 10 again.
Go under 8 babies more than once and the mom becomes food or gets donated as a pet.

In large litters like these I like to feed some of the babies right away if I can though so she makes bigger babies, 17 kits fighting for 8 nipples really wears the momma out :P

Nearly all my girls have 13 every time. I haven't really had a problem with it. I will get a runt that may or may not make it every once in a while, but I feed it off if it starts looking really bad. I have a litter right now that I thought for sure I was going to lose the runt, but I really wanted it to live because it's a really neat color/pattern. I fed off a few other ones from the litter I didn't want to keep and the runt has doubled in size and looks much better.