Mycoplasma gallisepticum can be passed through the egg, although most probably would not hatch. I'm not trying to argue with you at all, but most of the literature says that respiratory diseases tend to show up around the age of 3 weeks in baby chicks. I really hope this doesn't sour you on getting more chicks. It's always nice to try hatching your own, but hatchery chicks can be very healthy, and a good way to start out. Some hatcheries such as Meyer Hatchery in Polk, Ohio will ship as few as 3-4 chicks for extra shipping. Personally, I like to get at least 15 to help with body heat. You may want to wait for summer heat to cool around the first of September. Here is a link to read about the common respiratory and other diseases: http://edis.ifas.ufl.edu/ps044