Serena Williams says on social media that she gave birth to a baby girl named Alexis Olympia Ohanian Jr. The tennis star posted about the birth on her Instagram and Twitter accounts. She says the baby was born on Sept. 1 and weighed 6 pounds, 14 ounces. One posting also says about the newborn, "Grand Slam Titles: 1." The 35-year-old Williams won her 23rd Grand Slam singles title at the Australian Open in January – while she was pregnant.