In order for something to be classified as an organism it has to be able to carry on the processes of life. That is the scientific definition.
The zygote does that unless it is one of those residual bodies mott described.
In order for it to carry on the processes of life it has to implant.
In order for it to continue carrying on the processes of life past the stage of the zygote it has to implant. Yes. That does not mean it was not carrying on the processes of life before. It is dead when it is dead and not before. Just as it is a human life when it becomes human life and not before. Or as opposed to what Dixie argued, it is healthy when it is healthy and not based on some future state of unhealthiness.
You can not define things as they are now based on what they will be tomorrow or were yesterday.
Brett Fa.... uhhh, let me pick another one... Drew Brees is a football player NOW. Tomorrow he may retire and no longer be a football player. But he still WAS a football player.