I am currently 10w0d pregnant. At 6w0d, an ultrasound showed two gestational sacs - one with a fetal pole and one that appeared empty. At 6w3d, an u/s only showed one sac which included a fetal pole and the other sac seemed to have disappeared. I read up on "vanishing twin syndrome" (VTS) and learned that there should be no adverse impact to the remaining embryo and that my body would likely reabsorb the content of the second gestational sac. That said, yesterday I experienced severe bleeding and the passage of large clots. I'm talking about 20 minutes worth of bright red blood that was flowing so strongly that the toilet bowl filled multiple times with blood and blood clots. I couldn't bring myself to look at the clots closely - I was terrified of what I would see. I assumed that I had miscarried the fetus I was carrying, but an u/s at the ER about two hours later showed that the fetus was fine, measuring perfectly and the little heart beat was at 164 bpm. Nothing I have read about VTS indicated that this type of thing would happen, but the u/s did not have any findings to help with the diagnosis. Could this have been the complete miscarriage of the one twin? How concerned should I be that this could just be the begining of a miscarriage of the remaining fetus?