Paid maternal leave is not just better for caregivers who experience the physical stress of childbirth and the exhaustion of raising a newborn; it also seems to help babies learn language, according to new research.

In a study of over 300 toddlers between the ages of 2 and 3, researchers found that when mothers had paid time off after birth, their children scored higher on linguistic-development tests. Furthermore, mothers with less education saw positive effects on infant-behavior scores, suggesting that paid leave had disproportionately positive effects on families with fewer resources. Thus, the authors argue that expansive paid leave could help reduce socioeconomic disparities.

"From lots of existing research, we know that caregivers play a very important role in providing a social context for children to develop and thrive," said Natalie Hiromi Brito, an assistant professor of applied psychology at New York University and a co-author of the paper, published March 23 in Infancy. "My question was, how does something macro like family leave have indirect effects on these important early experiences?"

The researchers recruited 328 mothers in New York and South Dakota who worked during pregnancy; 117 took unpaid leave, and 211 took paid leave. The parents completed evaluations of their toddlers using standardized measures.

The families' annual income range was substantial, from $3,000 to more than $100,000. But even when the researchers split the group at the median to analyze higher-income families and lower-income families separately, they still saw a significant difference in linguistic scores for the babies of mothers who had paid leave. The study did not find any correlation between the length of leave and the scores, although the majority of parents went back to work after 12 weeks whether or not the leave was paid. 

The parents completed evaluations using the Brief Infant-­Toddler Social Emotional Assessment (BITSEA), a measure of social- and emotional-development problems or social delays, and the Parent Report of Children's Abilities-­Revised, which measures the risk of linguistic and cognitive delays.

The language scores among children had the most variation: The highest score a toddler got was 124, the average was 82.26, and the standard deviation was 29.89. Toddlers scored about 14 points higher on language tests when their mothers took paid leave, according to the nonstandardized scores.

The study also revealed that paid maternal leave had a positive effect on BITSEA "problem scores" among disadvantaged families specifically. 

"Although, on average, the effect of paid leave on socioemotional skills was significant for all paid-leave moms, when we dug into the data a bit more, the real difference was only for mothers with lower socioeconomic status; in this case, education," Brito said. "Paid leave may be beneficial for all families, but perhaps higher-socioeconomic-status families have other financial resources or social-support resources to supplement the lack of paid leave. Whereas for lower-socioeconomic-status families, having this work-protected paid time may be more important because of the lack of resources to rely upon."

Currently, the U.S. has a patchwork system for post-childbirth leave that can vary from state to state, while the relevant federal policy, the Family and Medical Leave Act, only provides for unpaid leave. Moreover, the federal law's restrictive eligibility requirements shut out half of mothers between 18 and 34, Brito and her colleagues pointed out. 

The U.S., Brito noted, is the only high-income country without a standard paid-leave policy for caregivers who give birth. 

"This is a choice that our legislators have decided to continue to make," she said. "There is no argument against paid leave that is based in any scientific or economic fact." 

The study, "Paid maternal leave is associated with better language and socioemotional outcomes during toddlerhood," published March 23 in Infancy, was authored by Karina Kozak, Ashley Greaves and Natalie Hiromi Brito, New York University; Jane Waldfogel, Columbia University; Jyoti Angal and Amy J. Elliott, Avera Research Institute Center for Pediatric & Community Research and University of South Dakota School of Medicine; and William P. Fifier, Columbia University Medical Center and New York State Psychiatric Institute.