A startup says it helps parents pick healthier embryos. Experts say it’s not that simple

The decision of whether to have a child can be hard even under the best of circumstances. For those with a family history of debilitating disease, it’s often gut-wrenching. If only there were some way to answer the all-important question: Will my child be healthy?

To those potential parents, a San Francisco startup is offering a solution: a genetic test of their embryos so they can select the one with the lowest risk of disease.

“We help couples have healthy babies,” Orchid Inc. says of its tests for schizophrenia, Alzheimer’s, cancer and seven other diseases. As much as health information, the 2-year-old company sells peace of mind. “I was apprehensive about having kids due to my family history, but after going through our report I feel in control,” reads one testimonial on Orchid’s website.

Scientists say it isn’t that simple.

Peter Kraft, a Harvard professor of epidemiology, helped to develop the so-called polygenic risk scores that Orchid says are the backbone of its tests. He said the way Orchid uses them concerns him, raising the possibility that, for instance, parents...