The number of women who are leaving it late to have children is increasing, statistics show.
Conception rates are rising across the board
Office of National Statistics figures show the fertility rate in all age groups, except the under 20s, has risen.
But in 2003 the largest increases in fertility rates were recorded in women aged 35-39 and 40 and over.
There were 621,469 live births in England and Wales in 2003 - an increase of 4.3% on the 2002 figure.
This is the largest annual percentage rise since 1979.
The number of women having children in their 30s and 40s has increased sharply over the last 20 years - at a time when the birth rate has dropped for younger women.
In 2003, the fertility rate for women aged 35-39 and over 40 both increased by more than 7%.
The trend towards later pregnancy is particularly pronounced among the wealthier social classes.
Anne Weyman, chief executive of the Family Planning Association, said: "It's great that women feel confident enough to make decisions about waiting to have children until the time is right for them.
"With so many different options in terms of education, travel and employment, women are choosing to delay pregnancy until they are sure it's what they want.
"However, it's important women are aware their fertility declines as they get older."
But the figures also show that the number of younger women having children has risen for the first time in 14 years.
Women aged 25 to 29 were most likely to have had a baby during the year. The rate among this group was 96.4 live births per 1,000 women - an increase of 5.2% on 2002, and the first increase since 1990.
The fertility rate among women aged 30-34 increased by 5.6% to 94.8 per 1,000
Overall, the average age of pregnancy is now 29.4 years, and for first time mothers it is 27.4 years.
Earlier this year, the ONS reported women are having an average of 1.73 babies, an increase on the average of 1.65 children in 2002. The lowest ever recorded fertility rate was 1.63 in 2001.
The figures also show that over 41% of births were outside marriage in 2003.
Wales became the first country in the UK where more than half of births were outside marriage.
Almost all English regions recorded an increase in the total fertility rate of over 4% in 2003. The exception was the North East, where the rate increased by just 2.5%.
Births to mothers born outside the UK accounted for 18.6% of all births in 2003 - more than 50% higher than the proportion of ten years ago.