The number of teenagers becoming pregnant has increased by 2.2%, official statistics show.
British teen pregnancy rates are high
The number of under-18s who became pregnant in England and Wales rose from 40,966 in 2001 to 41,868 in 2002.
The government said the latest figures were a "blip" in a trend which had seen teenage pregnancies fall during the preceding three years.
Last year, the government announced it was providing £40m to fund the teenage pregnancy strategy up to 2006.
The data was published by the government's Teenage Pregnancy Unit.
It showed some parts of the country have seen sharper rises in pregnancies among under-18s than others.
London saw an increase of 4.8%, and the east - which covers areas from Luton to Suffolk - saw a rise of 2.9%.
However, there was little change in the number of pregnancies in the south east, and the rate fell by 2.1% in the south-west.
In 2001, 46% of pregnancies in under 18s were terminated. Figures for 2002 are not yet available.
The government has pledged to cut the rate of conceptions in under 18s by 50% by 2010.
A spokesperson for the Department for Education and Skills, which oversees the Teenage Pregnancy Unit, said: "The under 18 conception rate has fallen 9.4% since the introduction of the teenage pregnancy strategy.
"The strategy draws on the best international research evidence of what works.
"The marginal increase in the provisional 2002 data highlights the importance of strengthening implementation of our Teenage Pregnancy Strategy.
"The Strategy has been set out over ten years in the recognition that it takes sustained action over a long period of time to achieve the societal and behavioural changes required."
Anne Weyman chief executive of the Family Planning Association, said: "The work of the government's teenage pregnancy unit must be praised in its achievements to date and must continue to be fully supported in its efforts to reduce the number of conceptions to under 18s.
"The complex issue of teenage pregnancy will not be solved overnight. We are confident a steady downward trend can be maintained, given the many different initiatives being implemented to tackle this serious public health issue.
"The momentum must be maintained in order to give young people the choice of an alternative to early parenthood."