You may be too late, according to a leading fertility specialist.

Watch the moment of conception from The Human Body

According to media pundits, the next three weeks are the ideal conception period for a New Year baby.

Tabloid newspapers are expected to offer large sums for access to the first baby of the new millennium.

And radio and television plan to offer themed nights of romantic broadcasting to get couples in the mood.

Impossible plan

But critics have attacked the morality of aiming to have a child for publicity's sake.

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Among them is Professor Lord Robert Winston.

And he says many people have already missed their chance anyway.

This is because the average pregnancy lasts 281 days with a standard deviation of 10 days, he said. There are 290 days left until the millennium.

For many women, especially those with longer menstrual cycles, this means it is already too late.

It is as good as impossible to plan a child for the millennium in the first place, he said.

Professor Lord Robert Winston on the chances of success

And there was no point attempting to have a child from a cold start.

"It takes the average couple five months anyway," he said.

Giving birth on a particular date is very much a lottery. Only 5% of women given a date for birth actually do so on the appointed day.

The wrong reasons

Professor Winston criticised the motives of would-be millennium parents.

He said: "I find all this really a bit distasteful because for so many people in Britain the real problem is actually having a baby at all.

"What I think is sad is that we focus on the wrong things.

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"The truth is that in a year when we're considering the family politically and socially, 10% of the population are finding it extraordinarily difficult either to have a pregnancy or to get funding for NHS treatment to help them have a pregnancy."

Professor Winston did, however, offer some advice to couples hoping to conceive.

"The best thing is to have sex very often," he said.