Infection of the uterus by bacteria and viruses has been associated with miscarriages. Certain medications, alcohol and smoking, can increase the risk of miscarriage. It is speculated that abnormally low levels of female sex hormone Progesterone could be associated with increased incidence of miscarriage. Medical causes like Diabetes and Thyroid disease, can be associated with recurrent miscarriage.
Miscarriages are amazingly common.
The main symptoms of abortion are bleeding through the vagina, which may or may not be associated with cramping and pain in the lower abdominal area. The extent of bleeding may vary from slight and painless bleeding in case of a threatened abortion to severe bleeding with acute pain, in case of an ineveitable abortion. You should see your doctor if you have any vaginal bleeding in pregnancy. If the bleeding is heavy, and specially if there are clots or you have a lot of pain, you should talk to your doctor immediately. He or she will advise you about what to do next.