Vaginal bleeding in the first trimester of pregnancy can be caused by several different factors. Bleeding affects 20% to 30% of all pregnancies. , and many women wonder how much bleeding during pregnancy is normal. Implantation bleeding is a form of bleeding that takes place when the fertilized egg is implanted in the wall of the uterus, around the time of the expected menstrual period. Implantation bleeding is typically lighter than a usual menstrual period.Bleeding increases the risk of having a miscarriage (lose the baby). Of even more concern, however, is that about 2% of all pregnancies are ectopic in location (the fetus is not inside the uterus), and vaginal bleeding can be a sign of an ectopic pregnancy. An ectopic pregnancy may be life-threatening. All bleeding, but particularly heavy or period-like bleeding during early pregnancy should prompt a call to your health care professional for immediate evaluation.Implantation bleeding: There can be a small number of spots associated with the normal implantation of the embryo into the uterine wall, called implantation bleeding. This is usually very minimal but frequently occurs on or about the same day as your period was due. This can be very confusing if you mistake it for simply a mild period and don't realize you are pregnant. This is a normal part of pregnancy and no cause for concern.Threatened miscarriage: You may be told you have a threatened miscarriage (sometimes also referred to as threatened abortion) if you are having some bleeding or cramping. The fetus is definitely still inside the uterus (based usually on an exam using ultrasound), but the outcome of your pregnancy is still in question. This may occur if you have an infection, such as a urinary tract infection, become dehydrated, use certain drugs or medications, have been involved in physical trauma, if the developing fetus is abnormal in some way, or for no apparent reason at all. Other than these reasons, threatened miscarriages are generally not caused by things you do, such as heavy lifting, having sex, or by emotional stress.Completed miscarriage: You may have a completed miscarriage (also called a spontaneous abortion) if your bleeding and cramping have slowed down and the uterus appears to be empty based on ultrasound evaluation. This means you have lost the pregnancy. The causes of this are the same as those for a threatened miscarriage. This is the most common cause of first trimester bleeding.Incomplete miscarriage: You may have an incomplete miscarriage (or a miscarriage in progress) if the pelvic exam shows your cervix is open and you are still passing blood, clots, or tissue. The cervix should not remain open for very long. If it does, it indicates the miscarriage is not completed. This may occur if the uterus begins to clamp down before all the tissue has passed, or if there is an infection.Blighted ovum: You may have a blighted ovum (also called embryonic failure). An ultrasound would show evidence of an intrauterine pregnancy, but the embryo has failed to develop as it should in the proper location. This may occur if the fetus were abnormal in some way and not generally due to anything you did or didn't do.Intrauterine fetal demise: You may have an intrauterine fetal demise (also called IUFD, missed abortion, or embryonic demise) if the developing baby dies inside the uterus. This diagnosis would be based on ultrasound results and can occur at any time during pregnancy. This may occur for any of the same reasons a threatened miscarriage occurs during the early stages of pregnancy; however, it is very uncommon for this to occur during the second and third trimesters of pregnancy.Ectopic pregnancy: You may have an ectopic pregnancy (also called tubal pregnancy). This would be based on your medical history and ultrasound and in some cases laboratory results. Bleeding from an ectopic pregnancy is the most dangerous cause of first trimester bleeding. An ectopic pregnancy occurs when the fertilized egg implants outside of the uterus, most often in the Fallopian tube. As the fertilized egg grows, it can rupture the Fallopian tube and cause life-threatening bleeding. Symptoms are often variable and may include pain, bleeding, or lightheadedness. Most ectopic pregnancies will cause pain before the tenth week of pregnancy. The fetus is not going to develop and will die because of lack of supply of nutrients. This condition occurs in about 3% of all pregnancies.There are risk factors for ectopic pregnancy. These include a history of prior ectopic pregnancy, history of the pelvic inflammatory disease, history of Fallopian tube surgery or ligation, history of infertility for more than two years, having an IUD (birth control device placed in the uterus) in place, smoking, or frequent (daily) douching. Only about 50% of women who have an ectopic pregnancy have any risk factors, however.Molar pregnancy: You may have a molar pregnancy (technically called gestational trophoblastic disease). Your ultrasound results may show the presence of abnormal tissue inside the uterus rather than a developing fetus. This is actually a type of tumor that occurs as a result of the hormones of pregnancy and is usually not life-threatening to you. However, in rare cases the abnormal tissue is cancerous. If it is cancerous it can invade the uterine wall and spread throughout the body. The cause of this is generally unknown.Postcoital bleeding is vaginal bleeding after sexual intercourse. It may be normal during pregnancy.Bleeding may also be caused by reasons unrelated to pregnancy. For example, trauma or tears to the vaginal wall may bleed, and some infections may cause bleeding.