Pregnant Nicky Hilton Rothschild May Not Find Out Sex of Third Baby Per Mom Kathy's Advice

Michael Ostuni/Patrick McMullan via Getty Images Nicky Hilton Rothschild and Kathy Hilton

Mum's the word for Nicky Hilton Rothschild!

The 38-year-old heiress and fashion designer, who's expecting her third child with husband James Rothschild, says she "maybe" won't find out the sex of their baby ahead of his or her birth, on the advice of mom Kathy Hilton.

"My mom's very old-fashioned. She's like, 'I didn't find out for any of you kids. Please, it's the ultimate surprise in life, do not find out,' " Hilton Rothschild recently told E! News, during New York Fashion Week.

The mom of daughters Theodora "Teddy" Marilyn, 4, and Lily-Grace Victoria, 5½, also said she feels "pretty prepared," given that she has had two children already.

"I do have to start getting the room ready," she added.

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RELATED: Pregnant Nicky Hilton Rothschild Debuts Baby Bump: "Best Things in Life Come in Threes"

Hilton Rothschild and her financier husband will welcome their third child during the summer of 2022, her rep confirmed exclusively to PEOPLE last month.

The French Sole designer debuted her baby bump in a Feb. 2 Instagram post, wearing a black dress that hugged her stomach.

In the photo, Hilton Rothschild posed in front of a floral wall while cradling her stomach. Her dress featured a sweetheart neckline adorned with jewels.

"They say the best things in life come in threes. 👶👶👶," she wrote.

RELATED VIDEO: Pregnant Nicky Hilton Rothschild Is "Bumping Around" During New York Fashion Week — See the Pics!

While Hilton Rothschild found out the sex of her first child before Lily-Grace's birth, she previously vowed to wait until the birth of her second child.

At her baby shower for Teddy, held at Kathy's mansion in Bel Air, California, the heiress was even treated to both pink and blue cakes to cover all her bases.

The month before Teddy's arrival, Hilton Rothschild told PEOPLE that she and her husband had no preference on a boy or a girl, and had even decorated the nursery "all neutral."

That didn't mean she didn't have preferences, though. "I did love having a sister," she said of her own childhood with older sister Paris Hilton.