Hi Sherrie,
The fumes given off by the normal chemicals you will use in the darkroom to do the silver gelatin are not harmful to the fetus. They are no more harmful than using cleanser to scrub your sink, or vinegar in cooking. I would though use gloves or tongs when working with those chemicals. As for the respirator, you don't need it. With proper ventilation in your darkroom you will be fine. As for experimenting with other chemicals and alt.processes, read the warnings that come with that chemical. As for chemicals to avoid while pregnant do not ingest aspertame sweetened foods. Read the side of a diet soda can and know that the PKU test done at birth is the shortened term for the long term they warn about. OK offr that soap box.

Welcome and have fun here.