The proportion of multiple births has increased by 20% in the last decade, figures for England and Wales show.
Twins are more common
The statistics show that 15 out of every 1,000 pregnant women gave birth to more than one child in 2002.
In 1992, just 12.5 pregnancies out of every 1,000 resulted in a multiple birth, according to the Office for National Statistics.
Just over 40% of babies were born to unmarried women last year - more than four times the rate of 25 years ago.
Nearly 90% of births to teenagers in 2002 were outside of marriage. For women aged 20-24 the rate was 63%, and for the 25-29 age group the rate was 36%.
Women in their late thirties and forties are most likely to have a multiple birth.
In the 35-39 age group, 21.9 pregnancies per 1,000 resulted in a multiple birth. Among women aged 40-44, the figure was 21.1.
It is thought that the increasing popularity of IVF may be at least partly to explain for this rise.
The Human Fertilisation & Embryology Authority, which regulates IVF in the UK, published guidelines last month aimed at cutting the number of multiple births.
The ONS statistics also show that that there was a slight increase in the number of babies being born in 2002.
A total of 596,122 babies were born during the year, compared with 594,634 in 2001.
The average age of women giving birth continued to increase. In 2002, the average age was 29.3, compared with 29.2 the previous year.
The average age of women having their first baby increased to 27.3 years.
Overall, the average woman of childbearing age now has 1.65 children - a slight increase on the previous year, which was the lowest ever recorded.
The West Midlands has the highest total fertility rate at 1.75 children per woman. The lowest figure of 1.62 was recorded in the South West and North East of England.
The statistics show that fertility continues to increase for women in their thirties and early forties, while it is declining for women in their twenties.
Women aged 25-29 have the highest fertility rate at 91.6 births per 1,000 women in 2002.
However, this rate is decreasing, while for women aged 30-34 it has increased to 89.9 births per 1,000 women.
The highest teenage birth rate was in the North East of England, with 34.2
live births per 1,000 women aged 15-19, compared with the low of 21.2 births per
1,000 women aged 15-19 in the South East of England.