Recently in Israel, a woman was mistakenly implanted with an embryo that is genetically related to another couple. Unfortunately, this case is not an isolated occurrence, as other cases of embryo mix-ups have been reported in several countries, including the USA, China, the UK and various other countries within the European Union. Cases of mixed-up embryos are ethically and legally complex: the woman who carried the pregnancy and the woman who is genetically related to the resulting child—both of whom endured (...) emotionally and physically demanding infertility treatments—along with their partners, may be unwilling to relinquish parental rights over the child.This article explores four possible approaches, found in numerous common law jurisdictions, which can be used to address cases involving embryo mix-ups. Our analysis reveals several avenues through which legal parentage can be established. It can be done through gestation and the marital presumption, genetic connections, by adhering to the principle of the best interests of the child, or by recognising multiple individuals as legal parents. We review the advantages and disadvantages of each approach, but we have one clear recommendation: resolving embryo mix-up cases should be done proactively through the establishment of legislation and guidelines, rather than relying on post hoc individual court decisions. Such legislation and guidelines should guarantee the consistency of values throughout diverse reproductive contexts and mandate that fertility clinics and medical professionals provide individuals with comprehensive information regarding the potential risks associated with assisted reproductive treatments. (shrink)