A day after we told my mother we're expecting, Mom called me, sounding panicky. "You can't continue being vegetarian now that you are pregnant!" - she said - "Meat is a source of protein, and you need protein!"
To many, hearing that you are pregnant and vegetarian sounds as though you are terribly irresponsible towards your unborn child, depriving the little one of essential nutrients - even if you have been a thriving vegetarian for years and years. I, personally, am of the opinion that during pregnancy, the best thing you can do is carry on with a familiar, balanced diet.
Protein is one thing people tend to get especially worked up about - unnecessarily. Yes, of course we need protein. However, keep in mind that protein deficiency is very rare in our affluent culture. In fact, many traditional diets - even if not exclusively vegetarian - don't count on getting a significant part of the protein from animal sources. They are based on a wide variety of combined beans and grains, with a bit of meat or poultry here and there.
When my husband was growing up, chicken was served in their house once a week - on Shabbat. On other days, dinner was usually a bowl of thick soup with beans and vegetables, and plenty of bread on the side. All children grew up wonderfully fit and healthy. To me, eating meat every day looks unncesessary, unless you do particularly vigorous exercise.
Aside from that, a pregnant woman - vegetarian or not - might consider taking a gentle supplement. For myself, I found this especially crucial in the first trimester, when I often couldn't force much food down because of nausea. Nausea still hits me once in a while, and then I feel as though I'm not up to eating anything but a light salad.
To be entirely truthful, I will confess I ate salmon a couple of times since I became pregnant. Not because I think fish is indispensable - in fact I believe we must be very very careful about mercury when choosing our fish - but simply because I got an irresistible craving for salmon, and decided to go with what my body desired at the moment.
By the way, my blood work came back a couple of days ago - perfect. I have been vegetarian for many years, and I feel wonderful. I don't think there is any need for me to make a change now.