When do you find out the sex?

Previous moms and moms who already know, when did you find out about the sex of your baby? My doctor said I can find out as soon as 16 weeks, but I'm just wondering. It sounds silly but I'm so excited to find out because I want to throw a gender reveal party so my mom who is terminally ill with brain cancer can enjoy the excitement with us. She's now in hospice care and the hope would be that she could hold on to at least see the baby, but I know that's selfish. I just want her to be a part of this as much as possible :-/