The couple revealed that their daughter arrived late last week via cesarean and both mum and bub are recovering well.
The pair shared exclusive images of their precious new arrival with Women's Health.
The fitness stars behind workout app Sweat also took to Instagram to share the happy news and give some touching details about the delivery.
"I just stared into Tobis eyes the whole time during delivery, nervously whispering 'please let her be healthy, please be okay, please be okay' and Tobi kept repeating 'I love you so much - she’s going to be healthy it’s okay just breathe it’s okay.' We both were crying," Kayla wrote.
"In that second, we heard her cry for the first time, the doctors and nurses examined her quickly, bought her over to us and said 'she is absolutely perfect'. My doctor said 'Look at that hair and those cheeks! Amazing!'"
Kayla says Tobi went into "dad mode" straight away.
"I don’t even know how to describe how I felt in that moment. I looked over at Tobi who looked like the proudest Dad I’ve ever seen, with tears running down his face he gave me a kiss on the forehead and whispered “she’s so perfect, I love you”."
She also shared that she had a cesarean as recommended by her doctor.
"I was a little bit sore, but after a couple of days I was generally fine, just no lifting other than Arna. Now, I just need to rest, eat good food, drink lots of water and I’ll be okay!"
The couple have been together for over six years and announced the pregnancy in late December 2018.
“I’ve wanted kids ever since I met Tobi and it’s something we have always talked about," the 27-year-old said. "It turns out that when we were ready it was just perfect timing. I think he will make the most perfect father, I’ve never seen him so excited about anything. He has already planned the funniest fluffy outfits for our winter baby and he talks to my tummy every morning and night."
Watch the pregnancy reveal below