Officials at the National Health Services said a report found 25,600 women in Britain ages 40-49 gave birth last year, up from 22,200 five years ago, The Daily Telegraph reported.
There were more births in all age groups except among teens.
Overall the baby boomlet continued last year with a 6.3 percent increase in the total number of births since 2006/2007 to reach 669,000 in England. However, the birth rate increase appeared to be slowing with only a 0.1 per cent increase in the last year, NHS officials said.
Women delaying motherhood to get careers started and waiting to find the right partner were thought to be behind the increase in older moms -- along with an increase in in vitro fertilization treatments among older women, officials said.
Two years ago, a study by the University of St. Andrews and Edinburgh University, both in Scotland, found the "ovarian reserve," the potential number of eggs women are born with from conception to the menopause averaged 300,000, but varied from 2 million in some women to as little as 35,000 in others.
Study author Dr. Hamish Wallace said the researchers found 95 percent of women, by the age of 30, had 12 percent of their maximum ovarian reserve, but by age of 40 only 3 percent remained.