No fetal pole at 6 weeks 2 days

Had my first ultrasound yesterday, there was no fetal pole yet, they did say I have mild fluid in the endometrium, my ultrasound results say one or more fetus. Has anyone had this happen? Did they end up with a healthy fetal pole later on? I’ve also heard this could mean vanishing twin syndrome. I have had twins before so it’s possible. I’m just lost and the dr literally said to me to retest hcg in 2 days to make sure it’s still rising because then we know “if we have a live baby or dead baby”