A good candidate is someone, or a couple, who already knows the exact genetic change responsible for a condition in their family, confirmed through prior genetic testing of an affected family member or through carrier screening of both partners. The test cannot be used as an open-ended search for unknown problems; it is only as specific as the variant it was designed to detect.

The conditions considered for testing are severe, well-characterized disorders that cause serious illness, disability, or shortened life expectancy from infancy or early childhood.
Examples include:
• Severe blood and metabolic disorders: such as thalassemia major, sickle cell disease, and Tay-Sachs disease, where a child’s health is significantly affected from very early in life.
• Severe neuromuscular and multisystem conditions: such as spinal muscular atrophy and classic cystic fibrosis, both of which substantially limit a child’s health, development, and life expectancy without ongoing, intensive care.

Testing here is reserved for conditions that are severe and certain from infancy or early childhood, where the diagnosis, its course, and its impact on the child are already well established. Conditions that first appear later in adulthood, such as certain hereditary cancers or degenerative neurological disorders, behave differently: the age of onset is often unpredictable and can vary widely even within the same family, and by the time symptoms might eventually appear, medical surveillance, preventive measures, or treatment options are frequently already available to manage the condition, for cancer syndromes there’s a chance the disease might not manifest at all. Because the timing is uncertain and effective management already exists for many of these later-onset conditions, embryo testing is not used for this purpose here; the clinical case for it is far less clear-cut than it is for a severe condition already causing illness in early childhood.

Professional guidelines also generally do not support using this technology for variants of uncertain significance, for carrier status alone without symptoms, or for selecting non-medical traits. In India, the law is explicit on this point: testing may be used only to screen for known, pre-existing, heritable, or genetic diseases, and sex selection is prohibited except when it is medically necessary to avoid a serious X-linked disorder.