Typically during a pregnancy, the placenta will attach to the top of the uterine wall. This makes delivery easier for both the mother and the baby. However, there are some cases where the placenta attaches to the bottom of the uterine wall and close to the cervix. If the placenta attaches too low, it is known as placenta previa, and this can cause serious birth complications and dangerous bleeding of the mother during the birth.
Though the exact reasons why placenta previa happens are not completely understood, there are two specific behaviors of the placenta that are recognized as placenta previa causes. First the placenta must attach lower in the uterine wall than is typical for a pregnancy. However, even if a placenta attaches to a low section of the uterus, in most cases it will move upward during the pregnancy. If the placenta never moves upward, this causes placenta previa. The medical community has discovered a few risk factors that may cause a mother to develop placenta previa.
Uterine Scarring and Previous Surgeries
One of the best documented placenta previa causes is the presence of scarring in the lining of the uterus. Researchers are still not completely sure why uterine scarring causes the placenta to attach to a lower section of the uterus, but the connection has been proven. If the woman has had previous surgeries on her uterus, she has an increased risk for placenta previa. Some surgeries that have been linked to placenta previa include C-sections, dilation and curettage, and uterine fibroids removal. There is a small amount of evidence that suggests miscarriage and late term abortions may also cause placenta previa.
Large Placenta and Multiple Fetuses
If a placenta is unusually large, it may cause placenta previa because the large placenta is less likely to move up the uterine wall. The placenta may be large if the fetus is abnormally large and requires more nutrients or if the mother is having a multiple pregnancy, such as twins or triplets.
Older Age or Previous Pregnancies
Research has proven that the age of the mother and a history of pregnancies are also placenta previa causes. Generally, mothers over the age of 35 have a higher risk of developing placenta previa, and the more children a woman has already birthed, the greater the chance that placenta previa will develop during the next pregnancy. Though the connection between these risk factors is proven, researchers still do not know exactly why age and previous pregnancies cause placenta previa. In addition, if a woman has had placenta previa in the past, there is a greater chance that her next pregnancy will also develop placenta previa.
Other Placenta Previa Causes
Mothers who smoke or use cocaine have also shown higher rates of placenta previa. The reason why this causes placenta previa is not known, but the medical community does have a few theories. It is believed that smoking and cocaine use decrease the mother’s ability to provide oxygen and other nutrients to the baby. Because the mother’s blood contains fewer nutrients, the placenta must be larger in order to provide the amount of nutrients is necessary, and the large size prevents the placenta from moving up the uterine lining during the pregnancy.
If this theory is true, it suggests that other conditions that affect oxygen and nutrient delivery may be placenta previa causes. There are many different diseases and conditions that decrease oxygenation in the mother and fetus including anemia, high altitudes, heart disease, hypertension, and infection. All of these health problems may make placenta previa more likely during pregnancy or may make it worse than it otherwise would be.
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