I am not a professional jeweler and do not know about the effects of
fumes on the fetus, but here is my experience:
When I was pregnant I did not chance anything. I stopped soldering
and held my breathe around anything questionable. I would talk to
your doctor and tell her exactly what kind of fumes you will be
around and get her advice. My overall feeling about everything and
safety in pregnancy falls into this category is "If it looks unsafe,
then it probably is and if it feels unsafe it definately is."
Educate yourself and make a decision you are comfortable with. Maybe
if I had looked into it more I could have continued soldering, but I
did not feel comfortable with it so I didn't. I have seen pregnant
women working in mills around all kinds of fumes and apparently
thier doctor said it was okay, but I wouldn't have done it.
Good luck and congratulations on the pregnancy!