Though editing the genetics of human embryos has sparked intense debate in the past year, Swedish scientist Fredrik Lanner has started to edit healthy human embryos for the first time, NPR reports. Lanner hopes to find new treatments for infertility and miscarriage by using the gene editing technology CRISPR-Cas9. He’ll deactivate genes in the embryos to see what roles they play in early development. (U.K. scientists were given the go-ahead for similar research earlier this year.) Many worry that gene editing will lead to designer babies and new hereditary diseases, but Lanner says basic research like his is necessary to avoid those situations.