In reply to owena:
Not scientific, but based on my experience I was fine climbing up to about 6 months pregnant max with both my pregnancies
I stopped bouldering and routed instead, as I was certain that falling would not do me any good, plus I only seconded or top roped, no leading
I stopped at 6 months because my stretchy ligaments were making my wrists very weak and prone to injury
Oh, and I had to stop for a month or so around the 2-3 month mark due to morning sickness. Throwing up at Froggatt after seconding a HS made me realise I should lay-off when feeling that rough!