Experts point to a variety of factors to explain the high U.S. figure, including a cultural shift toward greater acceptance of single-parent child rearing. The U.S. also lacks policies to help support families, including childcare at work and national paid maternity leave, which are commonplace in other countries.
"When our parents married, there was a sense that you were marrying for life," said Edward Zigler, founder and director of Yale's Edward Zigler Center in Child Development and Social Policy. "That sense is not as prevalent."
Single parents in the U.S. were more likely to be employed — 35.8 percent compared to a 21.3 percent average — but they also had higher rates of poverty, the report found.
"The in-work poverty is higher in the U.S. than other OECD countries, because at the bottom end of the labor market, earnings are very low," said Willem Adema, a senior economist in the group's social policy division. "For parents, the risk is higher because they have to make expenditures on childcare costs."
The study pointed out that the U.S. is the only OECD country that does not have a national paid parental leave policy. Some states have started to adopt such policies, but most parents are offered 12 weeks of unpaid leave. This is particularly difficult for unwed mothers, who may not be able to afford to take time off, Zigler said.
"We have not built in the kind of national support systems for families and children that other countries have," he said.