Data published by the Office for National Statistics shows that the births to older mothers have almost trebled in England and Wales in the last two decades.
The official figures show that around 26,976 babies were born to women aged 40 and above in 2009 as compared with 14,252 in 1999.
"The birth rate has gone up by 19% since 2001 yet the number of midwives has risen by only 11% over the same period," said Louise Silverton, deputy general secretary of the Royal College of Midwives. "The figures also mask the fact that an increasing number of births are becoming more complicated, requiring more of midwives' time."
The official data also showed that birth rates for women aged 20 to 24 fell by 1.6% in the same period, but birth rates for women aged 35 to 39 and 40 to 44 continued to rise. The average age of a mother in the UK has risen to 29.4 years in 2009 as compared with 29.3 in 2008.