The birth rate in the United States dipped to a record low in 2011, led by a steep fall in children born to immigrant women, says a new report from the Pew Research Center in Washington, released on Thursday.

The report uses preliminary figures for 2011 from the National Center for Health Statistics that show the overall birth rate in the US was 63.2 per 1,000 women of child-bearing age.

According to Pew, that rate is the lowest since at least 1920, the earliest year with reliable records.

The overall US birth rate fell by 8% from 2007 to 2010.

The birth rate for women born in the US fell by 6% over the same period, but for foreign-born women it plunged 14%, with Mexican immigrant women showing the steepest fall at 23%.

The downturn in births to immigrant women reverses a trend where foreign-born mothers were accounting for a growing share of US births.

In 1990, foreign-born mothers accounted for 16% of US births. This rose to 25% in 2007, before falling back to 23% in 2010.

The most recent peak in US birth rates was when the Baby Boomers were born, reaching 122.7 in 1957, nearly double today’s rate.

After the Baby Boomer peak, the rate declined through to the mid-1970s, then flattened out to around 65 to 70 births per 1,000 women, until falling again after 2007, which the authors describe as the start of the Great Recession.

The start of the Great Recession also saw a sharp drop in the number of US births, which had been rising since 2002. This decrease was also led by immigrant women.

Between 2007 and 2010, the overall number of babies born in the US fell by 7%, largely due to a 13% all in births to immigrant mothers. In contrast, births to US-born women fell by only 5% in that period.

However, despite the recent fall in rates and numbers, mothers born outside the US still account for a disproportionate share of the country’s newborns, as has has been the case for the last 20 years.

For instance, in 2010, only 13% of the US population was born outside the US, and only 17% of women of childbearing age in the US are immigrants, but 23% of births in that year were to mothers from that group.

Population projections from Pew suggest immigrants will continue to play an important role in the growth of the US population.

They suggest that by 2050, 82% of US population growth will be driven by immigrants arriving in the country since 2005, and their descendants.

“Even if the lower immigration influx of recent years continues, new immigrants and their descendants are still projected to account for most of the nation’s population increase by mid-century,” says the report.

The total number of US births in 2011 is estimated to be 3.95 million.

Written by Catharine Paddock PhD