The shortage of eggs in the UK has been blamed on strict rules that cap payments to donors at £250. In America, the limit is $5,000 (£3,000). Another cause of the shortage is believed to be a new rule requiring donors to sign a register so that children can trace their biological parents when they turn 18. However, the World Egg Bank has a pool of about 50 donors who are prepared to accept the limited payments and to sign the register.