Placenta previa is characterized by abnormal location of the placenta at or near the internal cervical os (mouth of the womb). In many of the cases, the placenta is actually low lying in early pregnancy but appears to ‘move upwards’ as pregnancy nears term, due to development of the lower segment of the uterus. This complication arises in one out of every two hundred pregnancies at the time of delivery.
¬In total placenta privia, the placenta completely covers the internal os; whereas in partial placenta previa, only a part of the internal os gets covered. When the placenta lies within 2 cm of the os but does not cover any part of it, this is known as marginal placenta previa. A low lying placenta, which is present in the lower segment of the uterus but does not cover the mouth of the latter, can also complicate matters by causing excessive bleeding during labor.
A woman who has had a past history of placenta previa has a 4-8% risk of recurrence in one of the subsequent pregnancies. Women who have given birth to more than one child at a time or have been pregnant many times have greater chances of developing placenta previa. Increased maternal age, uterine tumors, and uterine scars due to previous abortions, Cesarean sections, dilatation and curettage, and surgeries to remove fibroids are all factors that predispose the occurrence of the abnormality.
Women with placenta previa usually present with recurrent and painless bright red vaginal bleeding. The onset of bleeding largely depends upon the degree of previa. On an average, women who develop the problem, usually present with its symptoms when the gestational age is about 30 weeks. However, one third of the cases may present earlier. Initially, bleeding may be minimal and cease spontaneously but can be profuse later.
Bleeding at onset of labor can occur with marginal placenta previa. On examination, the uterus is soft and non-tender in a majority of the cases. The presenting part of the fetus may be found to be high or displaced. A transabdominal ultrasound is the best investigative technique for detecting placenta previa and has an accuracy of nearly 95%. Once the condition is diagnosed, it is very important to monitor the state of the mother as well as the unborn child.
Hospitalization is a must. Physical activity should be limited. Douches, enemas, or sexual intercourse is not permissible. Corticosteroids may have to be administered to hasten and ensure the maturity of the fetal lungs. The delivery is usually conducted by Caesarean section when the fetus is mature or if the bleeding is severe. Common fetal complications of placenta previa are intrauterine growth retardation, premature birth, mortality, or malpresentation of the fetus.