Summarize the following:
You might experience some spotting in the early stages of pregnancy, but this occurs in many women. This spotting is due to implantation and it usually occurs within 12 days from the fertilization.  Implantation means that the fertilized egg it has attached itself and penetrated into the uterine mucosa, preparing for further development. Besides implantation bleeding (in many cases harmless), there might be some other diseases that can generate vaginal bleeding during this stage of pregnancy. Therefore, it's important to make your doctor aware of any bleeding and to undergo testing if necessary. Bleeding during pregnancy can be a sign of miscarriage. However, it is very important to know that not all women who have vaginal bleeding are suffering a miscarriage, so if you are experiencing this type of bleeding do not panic - just call your doctor.  It's important to be aware that a miscarriage also has other symptoms such as abdominal cramps (these can be very severe, having more intensity than normal abdominal cramps that many pregnant women experience sometimes) and you might see foreign tissue passing through your vagina. If this is the case, you should immediately go to the hospital. Another medical condition that might lead to vaginal bleeding (also associated with internal hemorrhage) is ectopic pregnancy. This means that implantation has not occurred in the normal place (the uterine cavity) but in the fallopian tubes.  After the implantation, the embryo grows and develops until the fallopian tube cannot support anymore. The ectopic tissue then ruptures, leading to a potentially lethal hemorrhage. This condition is much rarer than miscarriage. The main symptoms of an ectopic pregnancy include severe pain in the lower abdomen (caused by the rupture of the fallopian tubes), low blood pressure (caused by the loss of blood through the fallopian tube rupture ), tachycardia (also caused by the loss of blood, as the heart needs to pump faster because it has a smaller quantity of blood to work with). Another potential cause of vaginal bleeding is molar pregnancy – this is when abnormal tissue grows inside the uterine cavity instead of a fetus. This occurs as a result of a genetic abnormality.  Other signs of this condition (besides bleeding) would be a rapidly growing uterus (because the abnormal tissue grows much faster than a normal baby) or excessive nausea and vomiting. Another possible symptom is the presence of a foreign tissue protruding through the vagina, which looks like a bunch of grapes. Any vaginal infection due to unprotected sex can lead to vaginal bleeding during the first trimester. One of the most common vaginal infections is gonorrhea. Vaginal infections can cause bleeding as they lead to inflammation and blood vessel dilation, which makes the blood vessels more susceptible to rupture. Because the fetus is more developed in this stage, any vaginal bleeding could mean that he or the mother are in danger. There are some medical conditions that are associated with bleeding during this late stage of development, one of them being placenta previa.  This medical condition does not occur very often but it can generate a troublesome pregnancy. In placenta previa, the placenta (the anatomical structure that connects the fetus to the mother) is abnormally located, lower than usual, blocking the uterine cervix. A bleeding placenta previa does not cause pain, thus making it harder to diagnose on time; so if you have vaginal bleeding — even if it is not associated with pain — you should get it checked out. Placental abruption is a very serious condition that endangers both the mother and the baby.  This rare medical condition is caused by the disruption of the placenta from the uterine wall, causing hemorrhage due to the blood vessels rupturing. Other signs of placental abruption include lower abdomen and back pain,and  blood clots through the vagina. Another cause of vaginal bleeding is preterm labor. This occurs before the 37th week of pregnancy and requires immediate medical assistance.  You might experience some mucous-like vaginal discharge, sometimes associated with blood. This occurs when the mucous plug that normally covers the uterine cervix opening is expulsed. Contractions are also present, as is lower abdominal and back pain.

Summary:
Be aware that implantation can cause bleeding in the first trimester (first 12 weeks of pregnancy). Understand that miscarriages can cause bleeding. Understand that ectopic pregnancies can lead to bleeding. Know that molar pregnancies are a health concern. Be aware that vaginal infections can cause bleeding. Watch out for placenta previa in the second and third trimesters. Know that placental abruption is a serious concern. Understand that preterm labor can cause bleeding.