Serena Williams and fiance Alexis Ohanian introduce daughter Alexis Olympia

— -- Tennis star Serena Williams and fiance Alexis Ohanian have officially introduced their daughter, Alexis Olympia Ohanian Jr.

Williams, 35, took to her Instagram page to share a photo of the baby, who was born Sept. 1, as well as videos from various stages in her pregnancy.

The 6-pound, 14-ounce newborn, who has an Instagram handle of her own (@olympiaohanian), left the hospital after nearly a week, according to her mother, who said in the footage, which was also posted to Ohanian's YouTube channel, "we had a lot of complications."

"Welcome, Alexis Olympia Ohanian, Jr., we're so happy to meet you," Ohanian, 34, wrote today in an Instagram caption. "Our little girl is already mama's perfect sidekick."

This is the first child for Williams and Reddit co-founder Ohanian, who got engaged in December. The couple announced they were expecting in April.

The confirmation came after Williams shared a photo of her pregnant stomach on Snapchat with the caption, "20 weeks."

Williams said in July that the time off from tennis was a welcome change of pace.

“I’ve never had this time off before, or if I have I’ve been injured and it’s really different to be injured as opposed to be expecting,” she told ABC News. “I’ve been really enjoying my time off and getting ready for this new massive chapter in my life.”

ABC News' Katie Kindelan contributed to this report.