Scientists have found that healthy eggs need a tremendous amount of zinc to reach maturity and be ready for fertilization.
The find from Northwestern University could help physicians assess the best eggs for fertility treatment.
"Currently we can't predict which eggs isolated from a woman produce the best embryos and will result in a baby. Not all eggs are capable of becoming healthy embryos," said Alison Kim.
"Zinc helps the egg exit from a holding pattern to its final critical stage of development," said Tom O'Halloran.
Zinc levels were significantly higher in eggs than other important metals such as iron and copper. It was the only metal to change significantly in concentration during the maturation process.
The team also found that an insufficient accumulation of zinc caused all the eggs to pause prematurely before fertilizing.
However, the progression of the process was restored by returning zinc to the eggs.
The research will be published in the September issue of the journal Nature Chemical Biology.