Ms. Wences once bragged to a friend, as they walked on school grounds just before a snowstorm, that her father was the one who sprinkled the salt crunching under their feet. Her father, Enrique, later told her not to talk about his work.

“He said, ‘You don’t want to be like me, mija,’” she recalled, using a Spanish abbreviation for “my daughter.” “I want you to go to school. I want you to do better than me.”

Mr. Wences, 43, said he was self-conscious that he did not finish high school.

It was a regret that would power him through seven-day workweeks for 25 years so that his daughters could get an education. One of the happiest moments of his life was when Yoselin called him from her car in the parking lot of Wake Technical Community College, where she was studying for an associate degree, to tell him that N.C. State had accepted her transfer application.

Ms. Wences said that if she got pregnant now, she would probably have to drop out of college.

“I’d feel embarrassed that the sacrifices that my dad made up to this point would be going down the drain,” she said.

Between 2007 and 2017, the population of Hispanic women of childbearing age in Wake County grew nearly 50 percent, drawn by a booming local economy. Yet the fertility rate for Hispanic women dropped by about 47 percent, according to Dr. Johnson. The rate for women who were not Hispanic dropped by about 16 percent in the same period, he said.

Birthrates tend to follow economic cycles. The fact that the American rate has not picked up along with the economy in recent years has puzzled demographers. In a survey late last year, the top reasons young women gave for delaying children involved money — children were simply too expensive.

But several young women interviewed for this article said that was not the case for them. Many came from large extended families with aunts and cousins who would care for a baby if need be. Many of those women had been raised by siblings in Mexico as their parents worked.