The number of women in the United States who take maternity leave has remained stagnant for the past 22 years, despite factors that suggest it should be increasing, according to a new study.

The report, published in the American Journal of Public Health, found that approximately 273,000 women in the United States took maternity leave on average every month between 1994 and 2015 -- a number that showed no upward or downward trend during that time.

The researchers note that fewer than half of the women who took maternity leave were paid during it.

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Since 1952, the United Nations’ International Labor Organization (ILO) has called for at minimum 14 weeks of paid maternity leave for all employed women.

“The United States is one of the richest nations in the world, and we’re not even close to that,” study author Jay Zagorsky, author of the study and research scientist at The Ohio State University’s Center for Human Resource Research, told CBS News.

Zagorsky points to a 2007 analysis that found out of 173 countries, only four lacked paid leave: Liberia, Papua New Guinea, Swaziland, and the United States. That same report found that 98 countries require working women to receive at least 14 weeks of paid time off when giving birth to a child.

In the U.S., the Family and Medical Leave Act -- passed by the federal government in 1993 -- provides eligible employees 12 weeks of unpaid time off during the first 12 months after birth to care for a newborn.

Three states, including California, New Jersey, and Rhode Island, have since enacted paid family leave legislation, but these laws do not appear to have had any effect on the number of women taking leave, Zagorsky said.

The researchers culled data by using the Current Population Survey, which interviews about 60,000 randomly selected households monthly.

The report also found that the number of men taking paternity leave has tripled over the last two decades, though the researchers caution that it was a very low figure to begin with. In 1994, about 5,800 U.S. men took paternity leave each month, compared to 22,000 per month in 2015.

The results showed that 47.5 percent of women who took maternity leave in the U.S. in 2015 were compensated. This number is increasing, the researchers found, but only by 0.26 percentage points per year.

“At that rate, it will take about another decade before even half of U.S. women going on leave will get paid time off,” Zagorsky said.

Zagorsky said the best estimates from the data would be that around 10 percent of men and 40 percent of women take some kind of parental leave.

Health benefits of spending time with a newborn

A number of studies have shown the health benefits of allowing parents, especially mothers, to spend time with their newborns.

“It’s a very exhausting time. A newborn baby is not sleeping through the night. They require frequent feeding that wakes up the mom, who often times will not get themselves back to sleep quickly afterwards,” Dr. Rebecca Starck of the department of regional obstetrics and gynecology at Cleveland Clinic, told CBS News. “Sleep deprivation takes a huge toll on the human body and that physical exhaustion leads to mental exhaustion.”

Not having time off after giving birth can also factor into postpartum depression, a condition which 11 to 20 percent of women who give birth suffer from, according to the Centers for Disease Control and Prevention.

“Going back to work, adding that additional stress and anxiety for an already sleep-deprived mom can further worsen their post-partum depression, which then leads to other health problems like headaches, fatigue, anxiety, chest pain, and relationship issues potentially not only bonding effectively with their baby but also with their spouse and other loved ones,” Starck said.

Heading back to work too early can also hinder a woman’s ability to breastfeed. “Often times if you go back to work early, your milk supply hasn’t really established itself, so you pump and you’re not making as much milk and it gets very frustrating, which leads a lot of women to actually stop nursing all together,” said Dr. Leena Shankar Nathan, assistant clinical professor in the department of obstetrics and gynecology at the University of California, Los Angeles.

Pumping breast milk at work can also be difficult, she notes. “Employers are supposed to give women time and space to pump but usually it’s not adequate in terms of time needed to set up, pump, and clean all the supplies,” Nathan said.

Economic constraints of taking parental leave

Economics play a huge role in whether or not or how long a woman is able to take maternity leave.

“Most people live pay check to pay check,” Zagorsky said. “That can be very expensive in the United States to lose pay for a month or two or three, especially at a time after a child is born. Children are not cheap.”

Nathan said that despite paid leave legislation in California (where she practices) some of her patients are still unable to take the full time off, as it often does not completely replace the worker’s salary. Under state law, the average person taking paid family leave only receives approximately 55 percent of their usual pay, with a maximum cap of $1129 per week.

Women may also fear falling behind at work or losing their positions if they take maternity leave.

Experts say the increase seen in the number of men taking paternal leave is encouraging, though they note it is overall still very small.

They credit the shift to a growing number of households where both parents work and a shifting societal attitude of men being equal partners in parenting.

What does the future hold for parental leave in the U.S.?

Experts say the United States has a long way to go to catch up to the rest of the world in regard to paid family leave.

During his 2016 presidential campaign, President elect Donald Trump promised to provide six weeks of paid leave to new mothers.

“If Donald Trump went through with this, it might make a difference. Then again, if amount of pay is relatively low, it might not make much,” Zagorsky said.

Nathan notes that while six weeks paid leave would be a start, it doesn’t even come close to the 14 weeks recommended by the ILO.

“Our policy makers need to realize the importance of breast feeding and giving a woman the chance to heal after delivery,” she said. “It’s a huge process physically and emotionally. It’s extremely important for them to take time and there needs to be better recognition of that.”