Pending further studies, continued transfusion, even in those whose TCD velocities revert to normal, is probably indicated (Class IIa; Level of Evidence B). 5. In children at high risk for stroke who are unable or unwilling to be treated with periodic red cell transfu- sion, it might be reasonable to consider hydroxyurea or bone marrow transplantation (Class IIb; Level of Evidence B). 6. MRI and MRA criteria for selection of children for primary stroke prevention with transfusion have not been established, and these tests are not recom- mended in place of TCD for this purpose (Class III; Level of Evidence B). Less Well-Documented or Potentially Modifiable Risk Factors Migraine Migraine headache has been most consistently associated with stroke in young women, especially those with migraine with A meta-analysis of 21 studies (13 case-control and 8 cohort) reported an overall pooled RR of 2.04 (95% CI, 1.72 The risk was greater in migraine with aura (pooled adjusted OR for 7 studies, 2.51; 95% CI, 1.52 4.14) com- pared with the association of ischemic stroke and migraine without aura (pooled adjusted OR for 6 studies, 1.29; 95% A second meta-analysis of 9 studies (6 case- control and 3 cohort) reported a pooled RR of 1.73 (95% CI, 1.31 2.29) between any migraine and ischemic stroke.594 This study also found a significantly higher risk of stroke among individuals with migraine with aura (RR, 2.16; 95% CI, 1.53 3.03) compared with individuals with migraine with- out aura (RR, 1.23; 95% CI, 0.90 1.69; meta-regression for aura status, P=0.02).594 Furthermore, there was a significant risk among women (RR, 2.08, 95% CI, 1.13 3.84) but not among men (RR, 1.37; 95% CI, 0.89 2.11). 