Ge76 shouldn't worry. The cabin pressure during cruise on normal airliners is equivalent to 8000ft. That's about the altitude that the E-110 (and I assume Y-12) will cruise at, especially for a short 198 mile flight. You could even ask the pilot to keep the altitude low as a favor to you. In any case the flight will stay below 10,000ft; AFAIK that's required for unpressurized passenger aircraft (at least in the US).

Plenty of people living at 8000ft or higher bring babies to term without problems. Plenty of people fly while pregnant with no ill effects. The flights on the unpressurized aircraft should be no different, though they might be more fun in your case.

You can see the flight paths (including altitude) of some E110 flights here: http://flightaware.com/live/aircrafttype/E110