Marissa Mayer, the CEO of Yahoo, gave birth to identical twins early Thursday morning, she revealed in a post on her Tumblr. “Zack and I are excited to announce that our identical twin girls have arrived!” she wrote. The happy moment comes at a tumultuous time in the life of the nearly 20-year-old Internet behemoth. Mayer, 40, a superstar executive at Google, was brought in to head up Yahoo in 2012, and reimagine the company and its place on the Internet. Despite several high-profile moves, such as the costly purchase of Tumblr, many of her initiatives and management decisions have been criticized by tech industry observers. Just this week, Yahoo’s board reversed a plan to spin off the company’s investment in in the Chinese e-commerce company Alibaba and instead decided to sell off some of its core Internet businesses. In September, Mayer stirred controversy when she announced she would take only two weeks of maternity leave following the arrival of her twins, even though the company offers up to 16 weeks of maternity leave for new moms — a policy she personally helped to expand. Judging by the looks of her very brief birth announcement on Tumblr, it looks like she might already be back at work.