sick-lid boy

I got 5 platys to cycle a 20 gallon tank. They've been doing just fine... During the ammonia stage, the ammonia levels were always under 1.0 ppm, and I did frequent water changes whenever the level got close to 1.0. But now I'm getting HIGH nitrite readings (5.0) and have been doing 30-40% water changes every other day.. so far they have not shown any signs of stress or illness... But... I'm not absolutely certain, but it looks like TWO of them are pregnant... either that or extremely constipated. But two of them are looking rather fat with whitish bellies. What should I do? I've been getting high nitrite readings for about a week now. Is it possible that I'll get Nitrate readings before they have babies?

I do have a 55 gallon tank thats fully cycled with Cichlids, and I also have an uncycled 1 gallon desktop tank that has a Glassfish with Ick in it right now... but he's looking better and should be better within a day or two... I could put a breeder tank in the 55 gallon... put the babies in the uncycled 1 gallon, or hope the 20 gallon is cycled by the time they arrive. Any suggestions?