any fell runners out there??

I started running again September but have been a bit rubbish at sticking to training programme. Ive got two fell races coming up in December and I wondered if I would be ok to still race? I'm not running very fast (I'd say 10 min miling) and at the moment can manage 4-5mikes. 
Both races I have at Xmas are Fell Races, so very hilly and are approx 6 miles. I'm 6 weeks pregnant at the moment so will be 12 weeks by the time the first race comes round... is it safe to still race? 
I see a lot of articles saying it's safe to run if you were a runner before. But I've only just got back in to running this Sept! Before that I hadn't run for 18months!!xx