The controversial embryo tests that promise a better baby

“She has her mother’s eyes,” begins the advertisement, “but will she also inherit her breast cancer diagnosis?” The smooth voice in the video is promoting the services of Genomic Prediction, a US company that says it can help prospective parents to answer this question by testing the genetics of embryos during fertility treatment.

For Nathan Treff, the company’s chief scientific officer, this mission is personal. At 24, he was diagnosed with type 1 diabetes — a disease that cost his grandfather his leg. If Treff had it his way, no child would be born with a high risk for the condition.

His company, in North Brunswick, New Jersey, offers tests based on a decade of research into ‘polygenic risk scores’, which calculate someone’s likelihood of getting a disease on the basis of the genetic contributions of hundreds, thousands or even millions of single DNA letter changes in the genome.

Genomic Prediction and some other companies have been using these scores to test embryos generated by in vitro fertilization (IVF), allowing prospective parents to choose those with the lowest risk for...