Bit late to this one but accidently cycled 200 miles in one go when pregnant (well, the cycling wasn't an accident but being pregnant at the time was accidental. And I SMASHED it). No ill effects on either me or the baby.
However by 12 weeks or so each time I was bloody knackered and was mainly concentrating on eating, so not much cycling was done. Also don't forget that your hormones have all kinds of weird effects on your ligaments (relaxin being the main one) so go easy. So basically, if you want to, cycle, if you don't, don't.
Both my kids do love going in the trailer though.