The British Fertility Society (BFS) said the removal of anonymity for donors in 2005 might have led to the lack of volunteers, leaving Britain struggling to meet the demand for donated sperm. Some 400 patients need donor sperm every year and many clinics have long waiting lists or have been forced to stop providing services at all. Writing in the British Medical Journal, Mark Hamilton and Allan Pacey from the BFS suggested that more families could be created from a single donor. The current limit of 10 pregnancies per donor is designed to prevent siblings born from donation inadvertently having children together. The authors said that means a minimum of 500 donors are needed every year, but in 2006 there were just 307.