4th pregnancy first set of twins

Tanya
This was my 6 week ultrasound we could see baby A's heartbeat but baby B was just a dark circle. I'm wondering if anyone has had a similar ultrasound at 6 weeks. I've heard of people being pregnant with twins and one disappearing I really hope that doesn't happen I have my 8 week ultrasound on March 7th but I'm very nervous I'll go in and one will be gone or not developing