What happens to legal parentage of frozen embryos if the intended parents separate before using them?

A frozen embryo that hasn't been transferred and used to establish a pregnancy is not itself a child with legal parents — parentage only becomes a live legal question once a pregnancy results and a child is born. What separation before that point affects is control over the embryo itself, which is typically governed by the storage agreement signed with the fertility clinic and, where relevant, by any agreement between the people who created the embryo about what happens if they separate.

Clinics generally will not proceed with using a stored embryo without the consent of everyone who has a say under that agreement, so a separated partner's objection can effectively prevent the embryo from being used at all, regardless of what either person wants individually. If the embryo is eventually used — whether by one former partner alone, with a new partner, or through a surrogate — parentage would then be determined under the ordinary assisted reproduction rules based on who is actually involved in that later conception and birth. Anyone with a stored embryo and a separating relationship should review their clinic consent forms and get legal advice.