For Marianne Miller, 32, watching other kids play with baby dolls during her childhood was the first time she realized she never wanted to have children of her own.

"I could always see child rearing was a choice, and I knew immediately it was a choice I wanted to opt out of," Miller said.

Today, Miller is married and works as a voice actress in Los Angeles. She isn't alone in leading a "childfree" life. America's fertility rate steadily declined between 2014 and 2017, and 2017 marked the lowest rate in over 30 years, with 60.3 births per 1,000 women aged 15-44, according to the most recent data by the Centers for Disease Control and Prevention.

In a 2018 poll from Morning Consult for The New York Times of nearly 2,000 people ages 20 to 45, 36 percent of survey respondents who did not want children or were not sure about becoming parents said they wanted more leisure time. Thirty-four percent said they haven't found a partner to raise children with, and 31 percent can't afford childcare.

That means thousands of American women are turning their back on parenthood for reasons ranging from financial stability to lifestyle. Here's what you need to know about this growing trend:

'It's just not for me'

Mikaela Fleisher, 31, who lives in Harrisburg, Pennsylvania, said motherhood never felt natural.

"I have never felt drawn to have children of my own," Fleisher said.

Beyond not feeling connected to parenthood, Fleisher also enjoys the freedom of living a childfree life. When she is not working as a receptionist at a local animal hospital, Fleisher volunteers with animal rescue organizations and sleeps in on her days off. She also has chronic migraines, so she says caring for herself without also caring for a child works best for her life.

"Just because society tells us that we should grow up, get married and have children does not mean that it's the right thing for everyone to do," Fleisher said.

Society telling women they must have children is also on the decline, according to Laura S. Scott, author of "Two is Enough" and director of the Childless By Choice Project. She said American women used to face social isolation from friends and neighbors with children, but, for many, that stigma has dissipated with celebrities like Oprah Winfrey, Jennifer Aniston and Helen Mirren explaining their choice not to become mothers.

"We think everyone is going to love being a parent, but that's just not true," Scott said. "We have these role models where we can point to them and say, ‘Well she doesn’t regret it.'"

Both Miller and Fleisher said their parents have not pressured them about children, and although Miller said she has had some friends with children "disappear" because of busy schedules, she has always felt secure in her decision to remain childfree.

Women in the United States are not the only ones questioning whether parenthood is right for them. Fiona Thomas, 32, an author from Birmingham, England, said she has never felt "maternal," and she agreed that she and her husband both feel a sense of freedom without children. In 2017, England and Wales saw the lowest number of live births in over a decade, according to the Office for National Statistics.

"I've never felt that uncontrollable urge to have kids so I always assumed it wasn't in the cards for me," Thomas said. "I enjoy the freedom. I also enjoy getting to be selfish a lot of the time."

Higher education, careers

Women are choosing higher education and career opportunities in the face of the high costs of raising a child, according to Brady Hamilton, a statistician at the National Center for Health Statistics.

Many women who pursue higher education do have children, though, and at increasing rates. Between 1994 and 2014, the percentage of women with a Ph.D aged 40 to 44 who had ever given birth increased from 65 percent to 80 percent, according to the Pew Research Center. But, overall trends still point to American women having fewer children later in life, with nearly 500,000 fewer babies born in 2017 than 2007, The New York Times reported.

"There's a lot of factors that go into the choice of whether or not to start a family," Hamilton said. "People are asking themselves, 'Is this really a good time to have children?'"

The cost of raising a child is an estimated $233,610, excluding college tuition, according to a 2018 estimate from the Department of Agriculture.

Miller said that, although she does own her home and gives "150 percent" of herself to her career, without child costs she and her partner still "barely have enough money to make ends meet."

Children present more than a financial concern for Miller and Thompson. Both emphasized mental health issues. Thomas said her mental health made her think "more deeply" about whether having children was the right decision — especially if she couldn't take the medications during pregnancy that treat depression and anxiety.

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"Having a mental illness has definitely brought up more questions about whether having a family would impact my wellbeing," Thomas said.

Scott agreed that the freedom women or couples without children feel extends beyond having to worry whether a babysitter is going to cancel.

"It's freedom in all aspects, in terms of personal freedom, financial freedom, the freedom to move around or travel," Scott said. "We're seeing people become more honest about the pitfalls of family."

Who will take care of me when I'm older?

Scott said one of the worries childfree women often have is wondering who will care for them when they are older and can no longer maintain their own home.

"People do worry, 'What happens when I get old?'" Scott said. "There's a perception that not having kids is a state of arrested development until you get old."

But Scott added that the women choosing not to have children who she works with are actively planning for retirement decades in advance. Plus, women can save their money not spent on children to live safely and comfortably as they age.

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Thomas said she and her husband also worry about being "lonely" as they age, since they do not live near any family.

"That sense of community is really important to me, and I do worry that I'll be missing out when I'm older," Thomas said.

Fleisher and Miller agreed that the idea of a family to rely on in your later years can mean something different to everyone, regardless of whether that means children, pets, a partner or other friends and family. Miller said she tells women considering the decision not to have children that it is "something you know in your heart whether you want to do."

"Our lives are entirely customizable," Miller said. "Ultimately, no factor other than your own wants or needs should come into question."