Almost half the pregnancies in girls aged 15 to 17 in Lancashire ended in an abortion.
The figures for 2007, which are the latest available statistics, show the number of teenagers becoming pregnant is on the rise – and so are the number of terminations.
A total of 999 girls aged between 15 and 17 became pregnant during 2007 and 469 ended up having an abortion, a 10% rise in terminations on the previous year.
A Lancashire County Council report links abortions to "alcohol and risky sexual behaviour" while revealing live births have dropped from 63% to 53%.
County bosses are concerned and baffled at the rise, meaning 41.9 of every 1,000 girls aged 15 to 17 conceive – compared to 41.7 nationally.
Hyndburn comes out top with 60.9 out of 1,000 girls aged 15 to 17 falling pregnant, followed by Burnley and then Preston, where the figure is 52.4.
There have been major rises in rates in South Ribble, where under-18 conception rates have shot up by more than 20%, and the Ribble Valley, where the figure is 10%.
Wendy Hemsworth, who is in charge of tackling conceptions for the under 18s at Lancashire County Council, said the authority was working with youngsters and other groups such as the NHS to combat the rise.
She said: "I think we are disappointed that the rates have gone up and I think, in respect of an enormous amount of hard work going on in the county with the county council and its partners in the NHS primary care trust, we will address this issue.
"The report mentions how we are following a national trend, though Lancashire didn't go up as much as the national rate. I wish I could explain the rise."
She added: "We are always concerned with young women who are pregnant and then do not want the child. We need to concentrate on the importance of relationships so it's more than giving information about contraceptives.
"We have got to get the message across that it's better to delay sexual activity until they are ready and mature for it."
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