Proponents of gender selection say that it can help parents to avoid the heartache of producing children with genetic defects.

It is a short step from saying people have a life that is not worth living to saying that people should not exist

Dr Richard Nicholson

Many devastating genetic disorders can only be passed on to children of one particular sex.

For instance, only boys suffer from haemophilia and muscular dystrophy.

The latest technique allows scientists to separate out sperm that will produce girls, from those that will produce boys.

This enables parents to chose to have a baby who will not be at risk of defects.

Societal reasons

However, there is disquiet over the use of the technique to enable parents to select the sex of a child for purely social reasons.

This may be a simple question of wanting a balanced family. For instance, a couple who have had several boys may want to ensure that next time they have a girl.

However, there may be more profound reasons. In many parts of India, for instance, intense economic and social pressures act to make sons much more desirable than daughters.

The results of this pressure were alarmingly illustrated by research carried out in the Punjab and published in the British Medical Journal.

The researchers found that most families who asked to be told the sex of a developing foetus did so because they planned to abort if it was a girl.

Critics fear that if sex selection became widely available it could, in certain, cultures lead to many more boys than girls being born.

Already in India, only about 920 girls are born for every 1,000 boys due to selective abortion.

Eugenics

Dr Richard Nicholson, editor of the Bulletin of Medical Ethics, told BBC News Online, that he had serious misgivings about sex selection.

He said: "We are moving swiftly down the path to saying it is alright for humans to select what sort of offspring they have, and that could rapidly lead into the field of more disreputable eugenics.

"Perhaps that will have no ill effect for individual families or children, but it carries considerable danger in terms of the way it changes society's attitude.

"It is a short step from saying people have a life that is not worth living to saying that people should not exist."