The 33-year-old Australian model suggested in an interview with The London Times that she and the 26-year-old Snapchat founder will remain abstinent until they wed.
"[I won't have another baby] yet. Not until after we get married. My partner is very traditional," she told the publication. "We can't ... I mean we're just ... waiting."
Kerr and Spiegel got engaged in July after a year of dating, and celebrated at their engagement party in November. The model had described their home life as quiet and domestic in a January 2016 issue of The Edit.
"He's 25, but acts like he's 50," she said of her beau. "He's not out partying. He goes to work in [Venice] Beach. He comes home. We don't go out. We'd rather be at home and have dinner, go to bed early."
Kerr was previously married to Orlando Bloom, and shares 6-year-old son Flynn with the English actor. She said in the December 2015 issue of Elle Canada that she and Bloom have learned to successfully co-parent since their 2013 divorce.
"The most important thing is that when he has time with me, we have quality time together, and when he's with his dad, he has quality time with him," the star explained.
"Being with my family, reading to Flynn, playing with him [is my idea of a good time]," she shared. "We draw together; we build blocks together. I also love swinging on swings. I'm a homebody. Being at home is the biggest luxury to me. I can't help it!"
Kerr is known for her work with Victoria's Secret, and recently modeled for Givenchy and Moschino. Singer Ciara and Seattle Seahawks quarterback Russell Wilson are among the other celebrity couples who waited to have sex until marriage.