The respiator is probably not necessary and the decrease in oxygen is no more than travelling to the mountains. By the way, you should avoid strenuous activity at higher elevations due to the hypoxia involved. Good ventilation should alleviate all risk from inhaled vapors. Gloves and tongs are a very good suggestion as some of the solutions can be absorbed through the skin. Using the respirator while mixing chemicals from powder form is another good idea. I have never heard of fetal problems related to the photographic darkroom, but I have not specifically researched the topic.