For Mr. Lopez, the ability to rear children is tied to his beliefs about masculinity. A man is many things, he said: strong, brave, a good dancer — but also, he’s supposed to be able to “have kids if that’s what he wants.”

Then there are the practical considerations, he added. Looking ahead 20 years, will he and his wife still be married? Will she even be alive?

“Maybe I meet a younger woman or something like that and she wants to have kids, and then I can’t give that to her,” Mr. Lopez said.

His wife, Sarah Kennedy-Lopez, 38, said she laughed when she and her husband first discussed these hypothetical scenarios, but even so, she understands where he’s coming from.

“Not all couples do make it,” she said, adding, “life does go on should a spouse die.”

Their children — a 7-year-old and 4-year-old twins — were conceived via in vitro fertilization, and her chances of getting pregnant without assistance are so low that neither of them uses birth control. So she isn’t pressing the issue.

“A couple times I have said to him, ‘Well, you know you could get a vasectomy and take care of that, so there would be no worries,’ and he says, ‘No, no, no — I’m not doing that. You can go and get your tubes tied,’” she said. “But I wouldn’t want to do that either, especially because I feel like I went through enough in conceiving our children in the first place.”

Studies have shown that men who receive vasectomies in the United States are typically white, non-Hispanic and live in the North Central and Western regions of the country. They also tend to have private insurance.