Any photographic course or class should be adequately organised from the point of view of safety. The important factors are that the room used for developing has forced extraction facilities, and that all participants use gloves and protective clothing.
The developer liquids that are used vary greatly, but most are considered safe to use in pregnancy as long as gloves and protective clothing are worn. There are some, however, that are not considered safe to use in pregnancy. Colour photography involves complex chemistry and there are many different developers that are used for this.
The sensible thing to do would be to talk to the person in charge of the course, and check with them that all the chemicals that you are using are considered safe for use by pregnant women. If there is concern regarding any of the chemicals that you have been using, you should inform your GP, who will be able to report the exposure to your specialist for further advice. There is a national organisation which looks into exposure to substances that might have harmful effects in pregnancy. This teratology service is based in Newcastle (0191 232 1525) and your GP or specialist might want to contact them for further specific advice.