Utah has the nation’s third fastest growth rate. Why? Babies. Lots of babies.

(Chris Detrick | The Salt Lake Tribune) Jenna and David Burrahm play with their daughter Faye, 14 months, in their apartment in Salt Lake City Wednesday, December 20, 2017.

Jenna Burrahm took five pregnancy tests just to be sure. With each pink plus sign, her excitement grew.

In early 2016, just shy of one year into their marriage, Burrahm and her husband, David, received the news they had hoped for. They wanted kids. Their Mormon faith encouraged it. And they thought, “Why not try?”

The couple’s daughter, Faye, is now 14 months old. Though they’re not in a rush, the Burrahms hope she’ll have at least three or four siblings.

“No matter what,” Jenna Burrahm, 23, said, “we wanted to have a family.”

According to new U.S. Census estimates released Wednesday, Utah is the third-fastest growing state in the nation. The reason: a continuation of its high birth-rate and big-family culture.

The Beehive State’s population increased by 1.9 percent — or slightly more than 57,500 people — from July 1, 2016 to July 1, 2017, mushrooming to a population of 3.1 million. It closely followed similar surges in Idaho (2.2 percent) and Nevada (2 percent). Washington state was No. 4 at 1.7 percent.

Most of Utah’s growth came from “natural increase,” meaning births outpaced deaths. That boom created 61 percent of the state’s new population. Immigration — primarily people moving around within the country — contributed to the remainder as a healthy economy attracted new job seekers.

But, though it still leads the nation, Utah is seeing a declining birth rate overall. The state slipped from 17.88 births per 1,000 individuals in 2013 to 16.59 just four years later.

That’s causing Utah’s leading demographer to doubt the accuracy of the U.S. Census estimates this year.

The federal report, based on mathematical predictions, estimates 379 more births in 2017 than 2016 (for a total of 51,461 this year). A state-funded survey using Utah Vital Records shows 1,202 fewer.

“We think they’re not getting that right,” said Pam Perlich, director of demographics at the University of Utah’s Kem C. Gardner Policy Institute. “We have better local data than they do.”

The state’s numbers would lower the natural increase to 54 percent of Utah’s new population — down from historical averages of around 66 percent. Even still, births remain the primary cause for growth in either model.

Perlich sees many potential causes for declining births, even though the state has the nation’s second overall fertility rate. Chief among them: couples choosing to delay having their first child, women seeking more education and more young members of the Utah-based Church of Jesus Christ of Latter-day Saints going on religious missions.

“In the past, you could pretty well estimate and project the population,” Perlich said. “It was basically a white man and a white woman and three or four kids and just a Xerox machine running. But that’s not the case any more. … It’s just become this really dynamic story of change and growth in Utah.”

The state ranked No. 1 for its population rate just last year, increasing then by 2.03 percent. In fact, Utah has been in the top 10 for its growth rate every year so far this decade.

It was beat out by Idaho and Nevada for 2017 as those states saw bigger increases in “domestic migration,” said Luke Rogers, chief of the U.S. Census Bureau’s population estimates branch. Utah had an estimated 17,568 people move inside its boundaries from other states and 5,019 from other countries.

Taken together, the populations of Western states expanded by 1 percent and now contain nearly a quarter of the nation’s residents. Perlich says the intermountain region is “a hotspot” that draws people with job opportunities and retirement getaways.

The country overall grew by more than 2 million people, for a 0.7 percent increase in population. The population for the United States is now 325,719,178.

Unlike the eight states that lost residents, including Hawaii, Alaska and West Virginia, Perlich believes Utah’s boom is “very sustainable, manageable [and] steady.”

Were its birth rates to rebound from the 2010 Great Recession, she added, it could top the nation for healthy growth.

For the Burrahms, they might not try for their second child for a few years as David seeks a graduate degree. But the Herriman family plans to add to the state’s population in future reports. Having Faye “brought new challenges and new happiness,” said Jenna Burrahm. “It just totally brought our family to another level.”