Baby Birdie weighed 10 lbs., 13 oz.
The couple first revealed their happy news in August, with a little help from their kids.
“SURPRISE … ” Simpson, 38, captioned an image of the couple’s children, as they prepared to pop two large polka-dot balloons to find out if they would be welcoming a little brother or sister into their family.
“This little baby girl will make us a family of five,” she added alongside a snap of her kids surrounded by smaller pink balloons. “We couldn’t be happier to announce this precious blessing of life.”
Opening up about how well her children were taking to the idea of a new sibling, Simpson told PEOPLE in October that “the questions I get on the daily from Maxwell and Ace are hilarious.”
“They want to know every detail — like how milk comes out of Mommy, how the baby will actually get here and if my belly button is a speaker to communicate with the baby,” Simpson added.
The star also noted that she and her husband “are constantly cracking up and trying to figure out how to be honest … but not traumatize them or the friends and teachers we know they are sharing every detail with!”
In honor of her daughter on the way, Simpson threw a “Birdie’s Nest” baby shower in January, revealing her baby girl’s name in the process, that was complete with a neon sign and whimsical table settings encouraging guests to “stuff your beaks.”
“It was a great day. Jessica is feeling very loved and she is ready for [Birdie] to come,” a source revealed to PEOPLE at the time. “She felt very loved, surrounded by her closest friends and her mom and her sister.”
“The shower was a bird’s nest theme to celebrate Birdie,” the source added, explaining that “Birdie is a family name” on the singer’s side.
Since then, Simpson has endured numerous pregnancy woes, ranging from broken toilets to a trip to the hospital.
At the beginning of March, the singer and fashion designer announced that she had returned home after spending a week in the hospital recovering from a bout of bronchitis
“After a week in the hospital for bronchitis (my fourth time in 2 months), I’m finally home! Coughing with Birdie has been a crazy painful journey,” wrote Simpson, adding that her “baby girl was monitored and is doing amazing.”
“I am on my way to healthy and counting down the days to see her sweet smile,” Simpson added, alongside a selfie of herself wearing a surgical mask.
Simpson has been chronicling various health problems stemming from her pregnancy on social media, including “severe pregnancy acid reflux,” a month of sciatica pain, and an extremely swollen foot she endured in January.
“Any remedies?! Help!!!!” she wrote on Instagram, as she asked fans for advice in alleviating the swelling.
The “With You” singer later said she managed to control the swelling by experimenting with cupping therapy, an ancient Chinese massage technique thought to increase blood circulation.
Although the pregnancy hasn’t been without its difficulties, a source previously told PEOPLE Simpson and her husband “are SO excited” about baby No. 3.
“Jessica and Eric absolutely thought they were done having kids after Ace was born — one of each was perfect,” a second insider told PEOPLE.
“We always practice,” the fashion designer told Entertainment Tonight, admitting they “don’t really know” if they’ll have a third child but that she is “very attracted” to Johnson, 39.
Despite that, Simpson quipped that another child “would definitely have to be a bit of a miracle” but that she had “baby fever” regardless.
“She went through a lot during and after her pregnancies,” a second source previously told PEOPLE. “Jess is such a great mom — Maxi is like her mini-me. Eric is the best dad too — there is a lot of laughter in that house.”