Blood Tests & Miscarriage Prediction: What You Need to Know

Question
My partner recently had an abortion without my knowledge. When I found out she said that she had been given a blood test that showed that she would have had a miscarriage had she chosen not to terminate the pregnancy.  Is this common? What sort of complications resulting in miscarriage can be predicted by a blood test given less than a month after conception? I respect her choice in the matter but I would like some clarification. Thanks.

Answer
Chris,
A blood test that would predict miscarriage would have to be done at least twice.  The blood test would moniter hCG (pregnancy hormone) levels in the blood, and compare values.  If the levels are rising at a rate consistent with pregnancy, this is a sign that the pregnancy is viable; if it is dropping or staying the same, it is an indication of miscarriage.  It would be unusual for a doctor to do a blood test and follow the levels unless they had some indication that there was something wrong with the pregnancy on ultrasound, or if she had symptoms of bleeding or spotting.  Blood tests are not done routinely in a normal evaluation.  
I hope this is helpful,
Doctor Joan