telling my mom I'm pregnant

I need some advice, I'm so eager to tell my mom but I don't know when I should. I have this idea in my head about doing it on my brothers birthday when I'm hanging out with my mom, and the only reason why I want to is because that day is a hard day for us because it's my brothers birthday and he passed away in 2014... I fee like it would bring a positive vibe to the day, but I don't want to take away from the day and make it about me... I just want to give my mother a reason to smile. So is it a bad decision to do it then? Or should I do it another day? Please I really need some help deciding.