Sexing gerbil pups

Question
my gerbils had six babies on 6/6/07. After one day, I checked on them and found only five, with no sign of the 6th. I can only assume his/her parents ate him. within the next four days, I found two others dead in the cage. Luckily I was able to remove them before the parents ate them. Is it normal to lose half the litter? I tried to keep a stress free environment, and even partially covered the tank with a towel to give then privacy. This is her first litter, so that may explain something. I now have three eleven day old pups, they all appear healthy but I am very bad at sexing them. I have looked at pictures on the Internet of eleven day old pups and their genders all seem obvious, but mine aren't so clear. They are all an orangeish color like their father. One pup has no visible nipples and possibly a little gap separating his genitals and anus (he seems obviously male). The other two are hard to tell. One has faintly visible nipples in between his/her front arms, and only a slight gap, but I can only see the two nipples and they are very faint. The third has nipples visible between the front arms and in the armpits. Do males have visible nipples at all at this age? Which of the two indicators is more reliable? The tiny little genitalia are so hard to distinguish I could be wrong about them. Any other known methods of sexing them at any age before sexual maturity is very helpful. Thank you for any advice, sorry for such a lengthy question!
~Hallie

Answer
It seems like you have one male and two females. I don't believe males have nipples at all. A female should have a very small gap to almost where it looks like only one hole. I believe you have sexed them right.
Also, it is normal to lose half a litter or even the whole litter. There are just things that may be out of our control that we can't handle.