Hi M.,
I am currently nursing my 2 and a half year old and my 9 month old. When we decided to try for the second baby, I was still nursing my oldest. There are no safety concerns about nursing while pregnant, unless you are in the last few weeks and are getting dangerously strong contractions while breastfeeding (but according to my midwife, even smaller braxton-hicks type contractions while breastfeeding are fine). Other concerns I've heard are that if you haven't started menstruating again, due to breastfeeding, it would be much harder to get pregnant. Also, the taste of the milk changes throughout the pregnancy as it's gearing up for feeding a newborn. So my daughter went through a few episodes when I was 5-6 months pregnant where she would start to suck and then make a face like it tasted bad, and then would stop at that specific time. But she kept coming back for more and she either adjusted to the taste or it kept tasting different. But to answer your question, there are absolutely no safety concerns about breastfeeding while pregnant, and many women nurse both their older child and the newborn (tandem nursing). I've attended a breastfeeding womens support group weekly for the last 2 years and this info is backed by the international board certified lactation consultant that runs the group. If you have any questions, please let me know. I hope that helps!