England and Wales has seen the highest annual rise in births for two decades, official figures show.
Births outside of wedlock has risen by 41%
The number of babies born last year rose by more than 4% to 621,469 - the highest annual birth rate since 1999 and the biggest rise since 1979.
The Office for National Statistics figures show more unmarried women are having babies than ever before.
The figures also reveal that women are having more babies and are waiting longer to become mothers.
The average number of children per woman is now 1.73 compared to 1.65 in 2002.
The average age of women that give birth has continued to increase, from 29.3 years in 2002 to 29.4 years in 2003.
Women are waiting longer to start a family with the average age of first-time mothers now 27.4 years.
The figures also show that the number of babies born to single mothers is about 10% higher than it was 10 years ago.
In 1993, 32.2% of births were outside marriage. In 2003,this figure stood at 41.4%.
Data for 2002 showed around 90% of births to teenagers occurred outside of marriage.
This compares to 63% of births to women aged 20-24 and 36% of births to women aged 25-29.
Norman Wells, director of Family and Youth Concern, said the trend in babies born to single mothers and women in cohabiting relationships was concerning. "Marriage is more than just a piece of paper," he said.
"Cohabiting relationships are much less stable than marriages and cohabitations with children are even more likely to break up than childless ones."
He estimates about 40% of lone parent families are created through the break up of cohabiting unions.
"Children born to cohabiting parents are more likely to experience disruptions in their family life which can have negative consequences for their emotional and educational development," he explained.
He said that statistically, children born to single parents were at higher risk of mental and emotional problems and were more likely to have trouble in school.
He called on the government to review its policy on teenage pregnancy and to do more to encourage the traditional family unit.
Anne Weyman, chief executive of the Family Planning Association, said: "The statistics show that the trend for women to have children later in life is continuing, and that families are being carefully planned to suit modern lifestyles. The rising number of births could just be a blip - we'll have to wait to see if it becomes part of a trend."