gestational sac containing a yolk sac but no embryo

hello! i am a first time mom, my LMP was last Sept.17,2019 and I am 6 weeks and 6 days pregnant but when I had my TransV ultrasound, the sonologist said there was a well-decidualized gestational sac containing a yolk sac but no embryo noted at that time. Is it normal not to see any embryo?