Michigan couple welcomes baby boy — their twelfth!

Kateri and Jay Schwandt were hoping for the girl.

Already parents to 11 boys — yes, 11 boys — the Rockford, Michigan, couple thought "the 12th time was the charm."

"We thought maybe, maybe, you know, we're going to have a girl. Number 12 could be the one," Kateri, who goes by Teri, tells Today.

It wasn't.

The Schwandts, who married at 18 and had their first child while they were college students, welcomed 7-pound, 12-ounce baby boy Tucker Ray Schwandt on Sunday. He joins big brothers Tyler (21), Zack (17), Drew (16), Brandon (14), Tommy (11), Vinny, (10), Calvin (8), Gabe (6), Wesley (5), Charlie (3), and 19-month-old Luke.

"Everyone says it’s crazy," Tyler, the eldest, says. "It's just normal, though. It’s how it is."

"I'm sure a little girl probably would be fun, but we know what we're doing," says proud mother Teri, clarifying that they're happy with all boys. "Sometimes I feel like I'm living in a locker room."

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"Having another baby in the house, it's just natural now," Teri tells Today. "We are confident that he is going to fit right in and we gave up a long time ago on a little girl showing up in this family."

While the Schwandts believe that having a big family makes sense for them — Teri is one of 14 children — they acknowledge that they "might" have stopped trying had their 10th been a girl.

"[If] we were going to have a girl, it would have happened by now," Teri tells MLive.com. "You don’t have 12 boys waiting for that girl."

They didn't find out the sex of any of their babies before they were born.

"It's always a boy, but it's always a surprise," she tells CNN.

Standford University's Amy Johnson explains how sex is determined in the womb:

"Almost everyone has around a 50 per cent chance of having a boy and a 50 per cent chance of having a girl," she writes. "What we can say is that dad's sperm determines whether a baby will be a boy or a girl. About half of his sperm will make a boy and half a girl. The sex of the baby depends on which sperm gets to the egg first."

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While some lifestyle factors might slightly influence these odds, so far scientists have found their effect to be tiny.

Teri admits that she assumed they'd have "only" seven kids. While the faithful Catholics occasionally used the natural family planning method to space out the births of their boys, she says they were mostly open to leaving the planning "up to God."

"We figure God knows what he's doing," she says.

"We were getting ready to leave the hospital and I said 12. Twelve kids, that’s crazy," Jay, who grew up with just one sibling, recalls.

Eleven-year-old Tommy is still holding out for a sister.

"We could adopt a girl," he suggests to his dad, clarifying that she'd have to be a tomboy.