Edwards' syndrome is rarely inherited and the condition is not caused by anything the parents have done.
The development of three copies of chromosome 18 usually happens randomly during the formation of eggs and sperm. There is an error in the division of cells, and the extra chromosome is either in the egg cell produced by the mother or in the sperm cell produced by the father.
As this happens randomly, it's extremely unlikely for parents to have more than one pregnancy affected by Edwards' syndrome.
The chance of having a baby with Edwards' syndrome increases with the mother's age.