What are the risk factors for miscarriage?

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), extremes of female age – early teens or 35 or over, smoking, uncontrolled diabetes or thyroid disease, a 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.