45 days pregnant, a sudden stream of fresh blood, often because the embryo is not well developed may be caused by miscarriage, but also just aura miscarriage, the bleeding is relatively small, if the situation continues to be to consider the possibility of ectopic pregnancy and other situations. 1. Embryonic arrest: a sudden stream of fresh blood, rather than a very small amount, often suggests that the embryo is not well developed, the incidence of miscarriage increases, need ultrasound to monitor the embryo to see changes. 2. Pre-eclampsia: a sudden rush of fresh blood may be pre-eclampsia, most of the pre-eclampsia will not bleed a lot, and may be followed by dribbling bleeding, and ultrasound is needed to monitor the embryo to see if it is continuing to develop. 3. Ectopic pregnancy: ectopic pregnancy people also have bleeding is a sudden stream of fresh blood, and then continue a small amount of bleeding may be, there are also bleeding is black, there are individual differences. Ultrasound is needed to check whether there is an extra-uterine mass or more pelvic effusion. Therefore, a sudden rush of fresh blood on the 45th day of pregnancy needs to be examined as soon as possible and diagnosed and treated under the guidance of a doctor.