"I am overjoyed to let you know our little girl is here," the 28-year-old wrote. "She is amazing! I love being a mammy & will fill you all in soon. Love Nadine xx."
Among the first to congratulate Nadine was her former bandmate Cheryl Cole. Minutes after the announcement, she tweeted, "It is OFFICIAL!! There is a baby Aloud!!!! Congratulations @nadinecoylenow & Jason so amazing!!"
Nicola Roberts wrote shortly afterwards, "There is a little baby Aloud! Congratulations @NadineCoyleNow & Jason on your little baby girl. I'm so happy she's here and healthy <3 xo."
Nadine announced that she and American footballer Jason, 35, were expecting a baby girl together on New Year's Day. The singer posted a picture of a stork-shaped balloon that read, "It's a girl" shortly after midnight.
Her fans assumed that she had given birth, and she was inundated with well-wishes before assuring her followers she had not yet welcomed her firstborn.
"Thank you for all your lovely messages," Nadine wrote. "She is not born yet. That is a baby shower balloon. We can't wait until she is. Loads of love! xx."
Nadine announced her pregnancy last summer, but did not immediately reveal who the father was. Then, in an exclusive interview with HELLO!, she confirmed that she was back together with her former fiancé Jason, and that he was the daddy.
"I think we forgot to tell everyone we were together," she said. "When I said I was pregnant I though, 'Why's everyone wondering who it is?' Then I remembered, 'Oh yes, that's right. I do stuff on TV and people are confused.' So this clears it up!"