The four degrees of placenta previa 

·        Total placenta previa-the placenta covers the entire opening to the cervix

·        Partial placenta previa-the placenta partially encroaches to within six centimeters of the cervix opening

·        Marginal placenta previa-the edge of the placenta is at the edge or margin of the opening of the cervix

·        Low-lying placenta/low implantation-the placenta is low in the uterine segment without the edge of the placenta actually reaching the cervix opening but is very close

The lower third of the uterus stretches and thins somewhat during the last trimester. This occurs to make room for the baby and prepare for birth. It is during this stage of pregnancy that bleeding occurs due to low-lying placenta previa because the edges of the placenta tears. In cases of placenta previa where the cervix is completely or partially covered, there will be bleeding as the cervix effaces (shortens) and dilates (opens) in preparation for the birth of the baby. 

Less than one-half of one percent of women with placenta previa suffers fatal complications, and nine out of ten babies survive. The risks for mother and baby are from the shearing off of the blood-filled placental attachments on top of the uterine opening, causing the mother to bleed. This can be dangerous to the mother if not managed. Repeated or severe bleeding can cause anemia and low blood volume in the mother. This can be treated with blood transfusions. For the baby the risk is from respiratory distress syndrome because it is delivered prematurely. It can also cause the baby to be small for gestational age (intrauterine growth retardation). Occasionally the blood loss is so great that not only does the mother need a transfusion, so will the baby. There appears to be a higher incidence of jaundice at birth in babies whose mother had placenta previa. 

Definite causes have not been established, but the following are common among women who have placenta previa: 

·        Previous pregnancy or pregnancies had placenta previa

·        Chronic hypertension, gestational hypertension or preeclampsia

·        Blood clotting disorder

·        Water breaks prematurely

·        Too much amniotic fluid (polyhydramnios)

·        Bleeding in early pregnancy

·        Multiple pregnancy (abruption occurs after first baby is born)

·        Car or other accident, assault with blows to the abdomen, trauma to the abdomen

·        Tobacco or cocaine use

·        Multiple pregnancies

·        Older mom

·        Uterine abnormality or fibroids

Proper medical monitoring of placenta previa can prevent serious complications. To keep the baby and mom safe, the baby may need to be born sooner or by cesarean.