More American women expect to have children some time in the future than they did in 2002, according to a federal study released on Thursday, which could point to a higher U.S. birth rate.

A survey by the U.S. Centers for Disease Control and Prevention (CDC) found that half of women aged 15-44 expected to have children, up from 46 percent in a 2002 survey.

"It's not a huge increase but it is a statistically significant increase," one of the study's authors, Jill Daugherty, said.

The increase could indicate a higher U.S. birth rate at some point in the future, Daugherty said. The new study did not examine what was behind the increase.

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The overall number of U.S. births declined slightly in 2015 to 3.97 million from 3.98 million the year before, according to the CDC. The drop followed an increase in 2014, the first since 2007, the agency said.

Since 2002, there has also been a slight decrease in the statistical average number of children women expect to have, from 2.3 to 2.2, according to the survey of 5,699 women.

As women age, their expectations for having children decrease regardless of how many children they already have, the study found.

More than two-thirds of married women did not expect to have a child in the future and 82 percent of women who already had two children did not expect to have another, it found.

The rate of births to teenage mothers in the United States has dropped dramatically in recent years to record lows.