When I was about 4 to 6 weeks pregnant I began to bleed one night. When I went to the hospital the doctor examined me and said I was having a possible miscarriage. The blood flow was very heavy but tapered off within a few hours. When I went to the doctor the next day he did an ultrasound and said there was a blood clot in my uterus which eventually went away. My question is: Was there a possibility I might have been carrying twins but wasn't far along enough to tell or was it just a blood clot and if so what causes blood clots?
It was probably a subchorionic hemorrhage, which is bleeding between the placenta and uterus, which often resolves over time. That's my best guess, but we'll never know. But it's gone, so that's the good news.