Loss after CVS?

Michelle • 3 IUI, 2 IVF, 2 FET, preg w/ boy EDD 5/3/18

I’m 11 weeks with twins and had a CVS this morning. Baby A’s heartbeat immediately slowed and stopped immediately after the procedure, baby B is fine. Has this ever happened to anyone? My MFM said it’s the first time it’s happened to him in 20+ years of practice. Can’t wrap my head around it.