Can wormer cause a mare to miscarry?

Question
I have a Quarter Horse mare who is roughly 11yrs old..I just recently purchased her and she was in foal. When I got her here to my barn I rode her for a few min and then put her up and rode her a few min the next day. I wormed her before I put her out in the field she was going to be in for the time being. I had a horse about 2 yrs ago that was bred and I didn't have any problems with her. I guess my question is...If wormer doesn't say any thing about "safe for mares in foal" can it cause the horse to miscarry or can it kill the baby and cause the mare to abort it or what? After I wormed her I went to the field to check on her and I found her colt laying on the ground looked to be roughly 5-6months along. You could see the ears, hooves tail bone and every thing...didn't have any hair though. Or could it be she lost the baby due to stress or what?

Answer
If the wormer did not have a disclaimer about being safe for pregnant mares, it is possible that the wormer was the cause but, it could have been a combination of worming, being stressed at her being moved and in a new environment, other horses, etc.  You may wish to have the veterinarian do a necropsy on the foal to determine the cause of death and ease your mind besides the fact that the mare could have an infection that needs to be treated.
I am sorry that you lost your foal and hope you have better luck next time.