There was a suggestion some years ago that exposure to increased temperature during the first 3 months could cause foetal abnomalities, including increased chance of spina bifida - that was the medical advice which was spread around over the last 10-15 years but am not sure what actual evidence there is. One would also need to consider the chemcial effects of chlorine etc. I do know of a Physio who has lost all her body hair having worked daily in a pool for some twelve months - I am not a chemist to be able to work out why but it may help to run it by a biochemist.