"My sweet Sailor Grace was born yesterday," she wrote on Thursday. "Our family couldn't be more complete."
RELATED GALLERY: See photos of Bristol Palin
Bristol Palin welcomes a baby girl
afternoon cuddles with my girl
30 weeks with my baby girl 💕
Stop growing my little chicken nugget 😩😖 only thing I need in life ❤️❤️ #threepostsoneday #askmehowmuchicare
Happy Mother's Day big mama!!!
Bristol Palin, left, and Karina Smirnoff pose for a photo at the Just Dance 4 launch party hosted by Ashley Benson and Christina Milian on Tuesday, Oct. 2, 2012 in Los Angeles. Just Dance 4 hits store shelves on Tuesday, Oct. 9, 2012.Â (Photo by Jordan Strauss/Invision for Ubisoft/AP Images)
Bristol Palin arrives at the Just Dance 4 launch party hosted by Ashley Benson and Christina Milian on Tuesday, Oct. 2, 2012 in Los Angeles. Just Dance 4 hits store shelves on Tuesday, Oct. 9, 2012.Â (Photo by Jordan Strauss/Invision for Ubisoft/AP Images)
FILE - In this July 27, 2012 file photo, Bristol Palin attends the "Dancing with the Stars: All Stars" panel at the Disney ABC Television Critics Association session in Beverly Hills, Calif. Bristol Palin says she is engaged to Medal of Honor recipient Dakota Meyer. The daughter of former Alaska governor and former GOP vice presidential candidate Sarah Palin said in a blog post Saturday, March 14, 2015 that Meyer came to Alaska to film the âAmazing Americaâ reality show with her mother last year. She says Meyer is wonderful with her son Tripp. Meyer was awarded the Medal of Honor in 2011. (Photo by Todd Williamson/Invision/AP)
FILE - In this April 30, 2011 photo, Bristol Palin arrives for the White House Correspondents Dinner in Washington. Bristol Palin's home life in Alaska is the subject of a reality series starring the daughter of former vice presidential candidate Sarah Palin. Lifetime says it will air 10 episodes of "Bristol Palin: Life's a Tripp" later this year. The series will explore the pressures of raising her toddler son, Tripp, as she maintains her close relationship with the larger Palin clan, the network said. (AP Photo/Alex Brandon)
Bristol Palin signs her new book at the Mall of America Wednesday, June 29, 2011 in Bloomington, Minn. (AP Photo/Jim Mone)
FILE - In this Nov. 24, 2010 file photo, former "Dancing with the Stars" contestant Bristol Palin arrives for an appearance on ABC's "Good Morning America" in New York. The daughter of former Alaska governor Sarah Palin has a memoir published by William Morrow called "Not Afraid of Life," expected this summer. (AP Photo/Charles Sykes, File)
Contestant Bristol Palin and her dance partner Mark Ballas pose together at the 11th season premiere of "Dancing with the Stars," Monday, Sept. 20, 2010. (AP Photo/Chris Pizzello)
Bristol Palin, right, daughter of Republican vice presidential candidate Sarah Palin, is seen with her boyfriend Levi Johnston at the Republican National Convention in St. Paul, Minn., Wednesday, Sept. 3, 2008. (AP Photo/Paul Sancya)
In this July 25, 2009, photo, former Alaska Gov. Sarah Palin's daughter Bristol Palin holds her and Levi Johnston's son Tripp Johnston at the governor's picnic in Anchorage, Alaska. Tax documents show unwed mother Bristol Palin earned more than $262,000 for her role helping raise awareness for teen pregnancy prevention in 2009. The most recent data for The Candieâs Foundation thatâs posted online by research firm GuideStar shows compensation at $262,500 for the now-20-year-old daughter of former Alaska Gov. Sarah Palin, the 2008 Republican vice presidential nominee. (AP Photo/Al Grillo)
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Sailor joins 6-year-old brother Tripp, Bristol's son with ex-fiance Levi Johnston.