The Grammy award winner – who started dating the Spy Kids star in 2016 after they were set up by actress Chloe Grace Moretz – is delighted she has a girl.
The Mother performer – who got engaged to Sabara on December 21, 2017, the day before her 24th birthday, after he popped the question under a Christmas lights tunnel – said: “It feels surreal.
“I’ve dreamed about this for so long, and now I’ll look at her and still can’t believe she’s real. My heart feels fuller than I ever knew it could.”
Trainor and Sabara – who got married in front of 100 close friends and family in a backyard ceremony at their Los Angeles, California, home on her 25th birthday – used a surrogate to welcome little Mikey into the world because it was the “safest” option.
Trainor explained: “It wasn’t our first choice, but we had endless conversations with our doctors on this journey, and this was the safest way for us to be able to continue growing our family. We are forever grateful for that option.
“I want people to know that surrogacy is just another beautiful way to build a family. It’s not something to whisper about or judge. It’s rooted in trust, science, love and teamwork. Every family’s journey looks different, and all of them are extremely valid.”
On Wednesday, the mother-of-three announced the arrival of Mikey on Instagram.
She captioned a series of photos of the family bonding with the newborn with: “Our baby girl Mikey Moon Trainor has finally made it to the world thanks to our incredible, superwoman surrogate.
“We are forever grateful to all the doctors, nurses, teams who made this dream possible. We had endless conversations with our doctors in this journey and this was the safest way for us to be able to continue growing our family.”
Mikey’s older brothers chose her unusual middle name.
Trainor added: “We are over the moon in love with this precious girl. Riley and Barry have been so excited, they even got to choose her middle name. We are going to enjoy our family time now, love you all.”
The Made You Look singer has made no secret of her desire to have more children, and she admitted a year ago she was ready for “some daughters”.
She told People: “Where I am right now is far beyond anything I could have ever dreamed of.
“I always wanted a family. Check. Now I need some daughters.
“But I never thought I could be a pop star because I didn’t believe in myself.
“Now, 19-year-old Meghan putting out All About that Bass is stoked; she’s so proud, like, ‘I didn’t know you could do that’. It took 10 years to become brave, but I’m finally thriving.”