Michal Lev-Ram, reporting for Fortune: May 1 will be a happy day for Twitter employees -- at least those expecting a baby. The social media site is the latest tech player to offer so-called "gender-neutral" parental leave, guaranteeing any parent up to 20 weeks of fully paid time off. Other companies that have embraced such policies include Etsy, Facebook, and Change.org. The rationale? Family structures have changed, and allowing for more evenly distributed parenting equals happier employees, both male and female (within, of course, both heterosexual and same-sex couples).