1 in 11 babies born in America this year will be screened by a genetic test that didn't exist a decade ago.Biotech startup BillionToOne turned a simple but radical idea—detecting rare fragments of fetal DNA in a mother's blood—into one of the most widely used prenatal tests in the U.S. And they're not stopping there. The same approach could unlock something even bigger: early-stage cancer detection from a blood test, a breakthrough that could one day save millions of lives.In this episode of Hard Tech, YC's Jared Friedman sits down with David Tsao and Oguzhan Atay to hear how they went from half a lab bench to a $4B biotech company—and why they believe this is just the beginning of what their technology can do.