Who is a good candidate for PGT-SR, and what does it change about my chances of

[Anonymous]

Who is a good candidate for PGT-SR, and what does it change about my chances of a successful pregnancy?

[Genetic Counselor]

A good candidate is a person, or a couple, in whom a balanced structural rearrangement, such as a reciprocal translocation, a Robertsonian translocation, or a chromosome inversion, has already been confirmed through blood karyotype testing.

This is typically identified in a few clinical situations:
• After recurrent pregnancy loss: when a couple has experienced multiple miscarriages, current guidance supports offering chromosome testing of the pregnancy tissue first; if that testing was not possible, or if it shows an unbalanced rearrangement, testing of both parents’ chromosomes is then recommended.
• After a previous affected pregnancy or child: when an earlier pregnancy or child was found to have an unbalanced chromosome rearrangement.
• During infertility or family workup: when a rearrangement is found incidentally, or when a close relative is a known carrier.

Testing is not typically recommended as a routine, first-line step for every couple experiencing pregnancy loss. Current guidance notes that the benefit of testing every couple is limited when a couple has had fewer than three losses, has no family history suggesting a rearrangement, or when the woman is older than thirty-nine, since chromosome errors related to egg age become a more likely explanation as maternal age rises.

For couples who do carry a confirmed rearrangement, this testing does not increase the total number of eggs or embryos produced by an in vitro fertilization cycle; a carrier parent typically still produces the same overall mix of balanced and unbalanced embryos. What it changes is which embryo is chosen for transfer, by identifying the balanced embryos in advance rather than discovering the outcome after a transfer or during a pregnancy. Because a meaningful share of embryos from a carrier can be unbalanced, several eggs and embryos are usually needed to identify enough balanced embryos for transfer; current guidance for counseling suggests couples typically need at least four to five blastocysts on average to have a good chance of at least one balanced embryo being available, and this can vary considerably depending on the specific chromosomes and breakpoints involved. It is also worth knowing that no large, well-designed trial has yet directly compared pregnancy outcomes with this approach against simply continuing to try to conceive naturally with prenatal diagnosis, so the decision to pursue it is discussed individually with a fertility specialist and genetic counselor rather than presented as clearly superior for every carrier couple.

[Author]

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