Preimplantation Genetic Testing for Structural Rearrangements is a laboratory test performed on embryos created through in vitro fertilization, used to check whether an embryo has inherited a chromosome imbalance linked to a rearrangement already known to be present in a parent. Unlike Preimplantation Genetic Testing for Monogenic Disorders, which looks for a single altered gene, this test looks at the structure of whole chromosomes. It is used when a parent carries what is called a balanced structural rearrangement, meaning a piece of chromosome has broken off and reattached somewhere else in the genome, or a chromosome segment has flipped end to end. In a carrier parent, all the genetic material is present, just rearranged, so the carrier is typically healthy with no symptoms at all. The problem arises during the formation of eggs or sperm, when chromosomes carrying the rearrangement can separate unevenly, producing embryos with extra or missing chromosome material, called an unbalanced rearrangement.

The two most common types are the reciprocal translocation, where segments swap between two different chromosomes, and the Robertsonian translocation, where two entire chromosomes fuse together. A related situation is an inversion, where a chromosome segment is flipped in place rather than exchanged with another chromosome. Couples usually consider this testing after experiencing recurrent pregnancy loss, after a previous child was born with an unbalanced chromosome condition, or after a rearrangement was found incidentally during infertility workup or family testing. Research shows that balanced translocations are found roughly fifteen times more often in couples with recurrent pregnancy loss, in about 2 to 5 in 100 such couples, compared to about 1 in 600 people in the general population.

The key appeal of this approach is that it identifies which embryos carry a balanced chromosome complement, either completely normal or an inherited-but-balanced rearrangement like the parent’s, before a pregnancy begins, rather than discovering an unbalanced result mid-pregnancy or after a miscarriage. It does not treat the underlying rearrangement, and it does not guarantee a pregnancy or a healthy child in every other respect, but it directly addresses the specific chromosome imbalance risk created by the known parental rearrangement.