Nearly 600 school age children became pregnant in Brighton and Hove in the two most recent years for which figures are available.
The figures were given in a written answer to a parliamentary question asked by Hove Conservative MP Mike Weatherley.
In 2007 the government said that 328 girls aged 18 or under became pregnant and in 2008 the number fell to 270, making 598 over the two years.
The figures were collated by the Office for National Statistics and given in a reply by Nick Hurd, the Conservative Cabinet Office Minister.
The numbers do not include those who suffered a miscarriage or who had an illegal abortion.
Stephen Penneck, director-general of the Office for National Statistics, said that the figures on conceptions were estimates baed on the number of live births, stillbirths or legal abortions.