Having already had twins, you probably have heard of the vanishing twin syndrome so you could ask the OB/Gyn about that.
When I went for an ultrasound the OB found no baby and since I was 40, he was sending me for D&C. OK by law they have to do the bigger ultrasound test. I was having some cramping when anyone touched my stomach, so the rubbing was uncomfortable. I finally said its ok OB already said it was an empty pregnancy. I never saw anyone move so quickly to show me the screen, pointing out Baby A, and Baby B, and ultimately the fibroid tumor. Later I delivered twin girls 5'11" and 6'8"
They are now 18 and after years of homeschooling they are in college majoring in fine arts, and the other journalism.
God bless you and give you peace
K. SAHM married 38 years== adult children 37,32, and the twins.