Business is booming for the world's biggest sperm bank, Denmark's Cryos, which is struggling to meet demand despite a soaring number of donors and new offices opening around the world.

At Cryos headquarters in Denmark's second-biggest city Aarhus, chief executive Ole Schou smiles broadly, sitting at his desk adorned with pictures of cheerful babies as he speaks of the company's unexpected success.

Two years ago, he was ready to shut down the business, or at least move it abroad, because of a Danish tax authority proposal that would have required donors to declare income from their donations, thereby putting their anonymity at risk.

But when it became clear that this would sound the death knell for Cryos, tax authorities withdrew the proposal.

A year later, in 2008, the number of donors had grown threefold, from 30 a day to 100 at its four Danish offices in Aarhus, Copenhagen, Odense and Aalborg, while the number of men applying to be donors had risen from 350 to around 1,000.

Each year, Cryos exports 85 percent of its 15,000 to 20,000 sperm donations to more than 400 clinics in 60 countries.

But despite the rising number of donors, Cryos has a hard time meeting demand.

Around 10 to 15 percent of couples in the world are infertile, according to Schou. Added to that are single women nearing the end of their childbearing years who still want to have a family.

"We help a tsunami of highly-educated, single women who are more demanding, and who prioritized their careers and who want to have a child before it is too late," Schou says.

The phenomenon has surged in the past three or four years, and Cryos "can't meet the avalanche of demand from the western world".

A 55-year-old economist, Schou started the sperm bank in a tiny cellar office in 1987 out of a desire to help couples who couldn't have children.

Cryos, which means "freeze" in Greek and refers to the sperm conservation process, was originally started to help cancer patients who wanted to freeze their sperm before undergoing chemotherapy.

Cryos' sperm has produced more than 14,000 full-term pregnancies since 1991, and the company has received piles of letters of thanks from women around the world, Schou says.

And while the sperm from a Danish Viking with blond hair and blue eyes may be exactly what clients are looking for in northern Europe, it "is far from the ideal in other parts of the world". "That's why we've opened a franchise in New York and another one in Mumbai, in India."

(Agencies)