Jessica Simpson's Newborn Arrived at Almost 11 Lbs. — Was Her Big Sister's Birth Weight a Clue?
Jessica Simpson gave birth to her third child, daughter Birdie Mae, on Tuesday — and the baby girl weighed 10 lbs., 13 oz.
The baby girl weighed 10 lbs., 13 oz. — above the average weight for a newborn baby, which the University of Michigan cites as 7½ lbs.
The proud mom and dad are also parents to son Ace Knute, 5½, and daughter Maxwell “Maxi” Drew, 6½. The couple’s oldest child was also above average in weight when she was born, weighing 9 lbs., 13 oz.
“Maxwell was hoping to maintain her record of the biggest baby in the family and now Birdie has her beat by 1 lb.,” a source tells PEOPLE. “She’s so in love with her little sister.”
Dr. Colby Previte, an obstetrician-gynecologist at the University of Rochester, tells PEOPLE that the birth weights of siblings are often similar, even noting, “I remember one boy who weighed just one ounce more at birth than his older brother had weighed!”
“Interestingly,” she adds, “second babies — especially when they are boys — often weigh more than their firstborn siblings.”
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Previte also notes to PEOPLE that there are other factors at play that can determine whether a mother will give birth to a larger baby.
“If a mother was a large baby when she was born, if she goes past her due date or if she is older in age when she is pregnant, she is more likely to have large baby,” she says.
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The singer and her husband first revealed they were expecting in August, with a little help from their kids.
“SURPRISE … ” Simpson, 38, captioned an image of Ace and Maxwell 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 the siblings 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,” she added.
The star also noted that she and Johnson, 39, were “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!”