Can femoral hernias cause miscarriage?

Very unlikely: A hernia is only a defect in the wall of the abdomen. It may cause pain. It may get the intestine trapped. If you are having miscarriages this should be discussed with your ob/gyn doctor. Common undiagnosed diseases like celiac, hypercoaguble etc need to be evaluated. If you haven't been pregnant before see your doctor for a referral.

Not Directly: A femoral hernia would not interfere with your pregnancy unless bowel would get stuck in the hernia, requiring emergency surgery. This is very rare since the enlarging uterus occupies the pelvis, effectively "blocking" bowel from entering the hernia. Even with an emergency operation, a miscarriage is not inevitable. Best to repair hernias when not pregnant.