There are reports that some of the girls - none of whom is older than 16 - entered into a pact to have their babies together.

The girls and their families have so far made no comment. Officials are also investigating the ages of the fathers.

Some are believed to be in their twenties and could face the possibility of being charged with having sex with minors.

It is illegal to have sex with anyone younger than 16 in Massachusetts.

Disturbing

Some of the school's own staff believe the sharp increase in the number of pregnancies was no accident.

"Some girls seemed more upset when they weren't pregnant than when they were," Gloucester High School principal Joseph Sullivan told Time magazine.

Local officials say that nearly half of the girls had entered into a bizarre pact to have their babies together.

Dr Elizabeth Guthrie, a paediatric psychiatrist at New York's Columbia University, told the BBC that some girls might be viewing pregnancy as a fast-track to adulthood and independence.

"It may give you an opportunity for unconditional love and attention from the baby," she said.

Local teenager Amanda Ireland, a mother who has just graduated from Gloucester High School, offered a blunt warning to other girls.

"Don't try to get pregnant. People say they know what it's like because they have younger siblings, but they really have no idea," she told the BBC.

David Landry, a researcher at the Guttmacher Institute, a New York-based non-profit group focusing on reproductive issues, said the declining teenage pregnancy rate of recent years appeared to be reversing.

Birth rates for girls aged 15 to 17 rose by 3% in 2006, the first increase since 1991, according to preliminary data released in December by the National Center for Health Statistics.

This trend was highlighted on Thursday when Britney Spears' 17-year-old sister Jamie Lynn, star of a popular television show Zoey 101, gave birth to a baby girl, according to People magazine.

But Mr Landry cautioned against attributing the pact or the worrying statistics to Hollywood. Recent hits have included Juno, in which a teenager gets pregnant and decides to have the baby, and Knocked Up, a comedy about a one-night stand.

"The trend emerged before those movies," he said.

Source: BBC