months ago, I had a history of miscarriage, then I had my period again normally, my menstrual cycle is 30 days, 4 days is over. On December 18, I had my period, on January 17, it was due but it was late until January 25. I tested with a stick and saw 1 faint line and 1 faint line. I went for an ultrasound and did not see the gestational sac. On February 1, I went for an ultrasound and the doctor said he saw the gestational sac but it was not clear yet, so I should continue to monitor. In the doctor's book, my gestational age was calculated to be 6 weeks but the gestational sac was not clear and I was also bleeding a little black blood, I also told the ultrasound doctor but he did not say anything. Doctor, can you tell me that I have black blood when I am 6 weeks pregnant, I do not know if the gestational sac has any effect? What is the cause of my black blood, doctor? Thank you doctor.