What are the risk factors for miscarriage?

Early pregnancy: Miscarriages are very common in early pregnancy, up to 20% risk, usually due to a chromosomal problem. After the heartbeat is seen on ultrasound the risk drops. It drops significantly after the first trimester. Drug use, chromosomal abnormalities, multiple prior miscarriages and trauma are risk factors for miscarriage.

Many risk factors ..: There are many possible 'risk factors' for miscarriage but some women have no risk factors that can be identified ahead of time. Prior miscarriage(s), early teens or 35+ female age, smoking, uncontrolled diabetes or thyroid disease, personal or family history of blood clots, or autoimmune diseases like lupus may all increase the risk of miscarriage. At least one previous child decreases the risk.