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.