Hi,
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The condition that could result in your case is called as Rh incompatibility, if the baby forming in the womb is of Rh Positive blood group. For the first child, there may not be any problems and you might have a safe delivery (if you have not had earlier miscarriages). You should be given injection Anti-D or RhoGAM injection (special immune globulins) during midterm or within 48 hours of delivery of baby to protect you from forming antibodies. If this is not given, and antibodies get formed, then your second pregnancy will be a problem and can result in miscarriage or fetal death due to the antibodies.
Visit these links to learn more and to now about precautions:
http://www.nlm.nih.gov/medlineplus/ency/ar
ticle/001600.htm
http://www.umm.edu/ency/article/001600.htm
.
Discuss about these with your gynecologist as you plan for pregnancy.
Take care.