Births to teenage girls and unmarried women in the United States rose in 2006, helping to push total births to a 40-year high, a Centers for Disease Control and Prevention report showed Wednesday.
The number of births to teenage girls in the United States rose last year after a 14-year downward trend, to reach nearly 42 births per 1,000, the CDC report showed.
"That finding surprised us because we had a 14-year steady decline in the teen birth rate," said Stephanie Ventura, head of the Reproductive Statistics Branch at CDC.
"Even though the pace of the decline had slowed in the past couple of years, it was still declining, and this year's finding took us off guard," she told AFP.
The number of unmarried women who gave birth rose eight percent to a record high of 1.64 million last year, but Ventura was quick to point out that the increase was not due to the rise in teen births.
"Back in 1975, about half the births to unmarried women were to teenagers," she said.
"But today, unmarried mothers and teenagers are not synonymous: only 23 percent of births to unmarried women were to teenagers," Ventura said.
"What fueled this increase was mainly births to adult women, in their 20s."
The report also showed that the United States had seen the largest number of total births last year in more than 40 years, and the highest fertility rate since 1971.
"The fertility rate summarizes the birth rates at each age group and tells you that if women today have children at the same rate by age throughout their childbearing years, they'd end up with 2.1 children," Ventura explained.
"That is the point at which the population will replace itself and is the highest the fertility rate has been since 1971," she said.
"What drove us past the replacement rate is the fact that the birth rate increased for all age groups," she added.
Total US births in 2006 were just under 4.266 million, or 127,647 more than in 2005, and the most since 1961.
The statistics used to compile the report were based on 99.9 percent of births in 2006. The findings of the final report, which is due next year, were not expected to be different to those published Wednesday, the CDC said.