JOHN YANG: Last year, the U.S. birth rate hit a record low.

But data suggests that over the past 30 years, the number of adults who want or wish they had children has remained relatively stable.

So why aren't they having children or expanding their families?

Ali Rogin explores some of the complexities of today's family planning.

ALI ROGIN: Over the past few weeks, we've been speaking with Americans who say they want to have a child or grow their families about why they're hesitant to do so.

Their answers were varied and complex, just like the solutions they said would help them change their minds.

CATHERINE CLARK, Washington, DC: I always wanted kids.

I love kids.

But economically, I don't really know of anyone who can swing it anymore.

Even parents that are working full time, they can't afford childcare.

They don't have a village to help them raise them.

CECILIA LA TORRE RAMIREZ, Alexandria, Virginia: I'm grateful that we are in like, a stable financial situation.

Still, it's difficult to raise a child.

We don't have any family close by.

We have friends who also have kids.

So they are also busy taking care of their families.

It's difficult.

We don't have anyone.

TREVOR WILLIAMS, Tulsa, Oklahoma: Every year, there comes out a new statistic of whether or not we've hit the turning point for climate change.

And that's something that I take into consideration when it comes to starting a family, because I don't want to raise a child in a world that every year gets closer and closer to becoming uninhabitable.

CAZOSHAY MARIE, Phoenix, Arizona: In May of 2017, I was struck by a car that was traveling 48 miles per hour while crossing the street.

And as a result of that, I ended up with several long term disabilities and conditions.

And really through this experience, my son actually became a caregiver to me.

Our roles were kind of reversed, and so that's not something that I would willingly want to be in another position to do again.

Would I be able to handle the parent teacher conferences, the transportation, making meals, changing diapers?

As a disabled person, those are all considerations.

ERICA STALEY, Chicago, Illinois: Pretty much as soon after having my first child, I agreed that weren't going to try and have a second with all the other uncertainties.

And that was heartbreaking.

We really did want to, and were kind of hoping that could be possible, but it just wasn't.

We had met with a financial advisor, and he was pretty clear.

You're either going to be able to afford childcare or retirement savings like, you can't.

You're not really going to do both in the next five years just because of the cost.

CATHERINE CLARK: Everyone is incredibly stressed out.

Everyone's incredibly broke.

We're all trying to help each other.

We're all grasping at straws.

And I don't know if I want that for my future.

TREVOR WILLIAMS: My sister, I know she spends about a quarter of her salary every month on childcare expenses, even with daycare expenses and such like that.

I know there's additional things such as putting extra food on the table and covering medical expenses.

CAZOSHAY MARIE: There are a lot of things that I think that the government, the society and community can do to kind of help with some of those concerns that are not just for me as a disabled parent, but I think for anyone who would be considering or hesitant to expand their family, that would be just offering more support, more community based support, as well as just the resources for the practical knowledge, parenting classes, things of that nature.

ERICA STALEY: If universal child care was an option, and we didn't have to worry about that, if universal healthcare was an option, and I wouldn't have to wonder if I can anticipate regular maternal care, high quality maternal care, while I was pregnant, then, yeah, we absolutely would have made an effort to expand our family.

For sure.

CATHERINE CLARK: We need rent subsidies because no one can afford it.

We need to be able to get the cost of food and housing under control because right now they are spiraling out.

CECILIA LA TORRE RAMIREZ: I think we need to have paid leave for all because many families are the sandwich generation.

You have to take care of your parents who are elderly, and you have to take care of your kids.

People work really hard.

It's not that we don't work hard, but it's not enough.

ALI ROGIN: For more on this topic, I'm joined by Karen Guzzo, a family demographer and the director of the Carolina Population Center at the University of North Carolina.

Karen, thank you so much for being here.

First of all, tell us about this moment that we're in.

Is it different than other times in this country's history that we've seen declines in fertility?

KAREN GUZZO, The University of North Carolina at Chapel Hill: That's a great question.

And so what I would say is we've seen fertility fall below what we call replacement level before, and the United States has come back up above this, above that sort of mythical two children per woman level.

What's interesting now, though, is that it's been sustained declines pretty much year after year since the Great Recession.

And so we're starting to think, as demographers, maybe the decision making that goes into whether people have children or going to have another one has changed.

ALI ROGIN: What are the factors weighing on people's minds these days?

KAREN GUZZO: Well, people are certainly not being selfish about deciding to have kids.

They're actually being really deliberate having children.

And so they're worried about their ability to combine work and family, their ability to provide for their future children, their ability to afford to give sort of a lifestyle that will suggest that their kids have opportunities for success in the future.

So they want to be able to afford to buy a house.

They want to send their kids to safe and reliable childcare centers and then ultimately safe schools.

They want a world in which they think climate change will not delay their children's chances of success.

And so they're giving these factors a lot of thought, and they're hard to measure.

In sort of the typical surveys that we used to use and some of the earlier theories, we had to kind of understand fertility.

ALI ROGIN: There's been a particularly steep decline in terms of births from people who are much younger to what do you attribute that?

KAREN GUZZO: The research really shows that for teens and those in their early 20s, traditionally, those births have largely been sort of unplanned and unintended.

And so, these are births that people are able to avoid having, avoiding getting pregnant in their late teens or early 20s, when perhaps they have less stable relationships, when they have fewer economic resources.

So this is good news.

The problem is that if people are avoiding having births at ages and in circumstances where we might think they are not ready to be parents, is to try to understand when they think they will be ready to have kids and make sure that we as a society have those conditions in place for them.

We need to make sure that they reach their later 20s and their 30s and feel like, okay, now I have what it takes to be a good parent, and I have the resources and life circumstances where I can, you know, go ahead and make those decisions.

ALI ROGIN: Sometimes we hear of people in these categories being labeled as selfish, or they're being insinuations that they're being selfish.

What do you make of those conceptions?

KAREN GUZZO: That's really not the case.

My research and the research of many others is showing that people have the set of prerequisites in mind that they want to be able to meet, to make sure that they are able to be good parents, that they are able to provide what their kids need, that they can meet the needs of their relationships and their family and friends.

And so they're really being quite considerate about this.

Being a parent is really hard in the United States, and we have declining social mobility.

And so people are being very careful about this.

If they think they can't give their kids good opportunities, they're willing to say, hold on, I should wait.

I'll wait till I have kids and tell them in a better circumstance.

ALI ROGIN: Lastly, what are some of the other solutions that other countries are trying to put in place to avoid continuously declining birth rates?

And is any of it working?

KAREN GUZZO: Well, there are countries that are offering cash allowances or tax breaks.

Those don't seem to be particularly effective.

The more effective policies are those that are kind of a package of deals.

So having a robust childcare infrastructure, one that people can find easily, they can afford it is high quality that's important.

Having parental leave for both mothers and fathers is important.

Most policies that are effective are the ones that grow the economy for everybody, but also have a strong social safety net that really makes sure that young people and young families have access to the resources they need, like childcare, like paid leave, but also aren't overburdened by housing costs or student loan costs.

ALI ROGIN: Doctor Karen Guzzo at the University of North Carolina, thank you so much for joining us.

KAREK GUZZO: Thank you for having me.