As far as I understand it, more embryos are created than required. These are then either destroyed or frozen. The creation and destruction of human embryos, or their suspension in a frozen state are serious moral and ethical questions.
"I've always been crazy but it's kept me from going insane Nobody knows if it's something to bless or to blame So far I ain't found a rhyme or a reason to change I've always been crazy but it's kept me from going insane"
Waylon
https://www.statnews.com/2024/02/22/alabama-frozen-embryo-ruling-threatens-ivf-clinics/ This article, from the pro-ivf camp, admits many more “fertilized eggs” are made than implanted. Such an “egg” is an embryo. (But these are the people who claim a “fetus” is not a child.) These excess “fertilized eggs” are then frozen or destroyed. Semantic redefinition is how clinicians deceive (e.g. the mRNA serum does not equal vaccine without the redefinition.)