Merlyn Glass (genetic nurse counsellor) answers:
When a mother is O negative, it means she does not have antibodies to a protein which is called Rhesus Positive. As your husband is O positive, your baby could be O positive or O negative.
If the baby is O positive, the mother can build up antibodies towards the baby's blood, and the baby can become anaemic. It is very important that your doctor checks to see if you have developed antibodies and monitor this carefully.
To prevent antibodies from developing, an injection, Anti-D is given to the mother either after a miscarriage, or a test like amniocentesis, or after each delivery. It is unclear as to why your doctor gave you anti-D at this late stage of your pregnancy, but it is very important to get the injection after the delivery of this baby.
If a mother is O negative, even if the baby is positive, there is not usually a problem with the first baby, unless she has not received Anti-D after and earlier miscarriage. Only if untreated with Anti-D, there could be problems with subsequent pregnancies if the babies are positive.
You also don't say whether or not you had any sonar examinations done- sometimes, if there is a problem with the negative/positive blodd groups, the doctor would pick up signs from the sonar. If the baby is negative, the mother will not develop antibodies, because the baby too, does not have the positive protein.