Pooled analysis of the 7 studies documenting TCD measurement before and after hydroxyurea therapy. The pooled analysis is based on the random-effect model demonstrating the average drop in TCD measurement after starting hydroxyurea therapy of 25 cm per second.^80,81,95-99  The table also includes the observation that the decrease in TCD measurements can be seen as early as 3 months after starting hydroxyurea therapy with a sustained impact of hydroxyurea therapy on decreasing TCD measurements for at least 36 months. The black diamond represents the results of random-effect models. The edges of the diamonds represent the 95% CI of the meta-analyses for the random-effect models.²⁶