Placenta Previa

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Placenta previa is a type of antepartum hemorrhage.

Antepartum hemorrhage is defined as bleeding from the genital tract that occurs after the 28th week of pregnancy till the birth of the baby.

Other Causes of Antepartum Hemorrhage are Abruptio Placentae / Placental Abruption and extra-placental causes like cervical erosion, cervical polyp, cervical carcinoma and varicose veins of the vagina or vulva.

Placenta previa is a condition where the placenta is implanted completely or partially in the lower part of the uterus.

The incidence of placenta previa is about 1 in every 200 pregnancies. In the USA, the incidence is 0.3-2.0%. It can go 1 - 5 times higher in pregnancies after a previous caesarian section.

Types of Placenta Previa

There are 4 types of placenta previa, classified according to the position of the placenta on the uterine wall.

  • Low lying placenta previa:Also called the Type 1 placenta praevia. In this type of placenta previa, the placenta is in the lower part of the uterus but does not reach the internal os of the cervix.

  • Marginal placenta previa: Also called the type 2 placenta previa, here, the edge of the placenta reaches the margin of the internal os of the cervix, but does not cover it. It is more dangerous if the placenta is implanted at the posterior or back wall of the uterus.

  • Partial placenta previa: The placenta covers the internal os of the cervix partially.

  • Complete placenta previa:The placenta lies over the internal os of the cervix, completely covering it.

Placenta Previa
Types of Placenta Previa

Risk factors for Placenta Previa

Certain factors can increase the incidence of placenta previa.

  • Age: The incidence of placenta previa increases with the age of the woman. It is 2 % in women over the age of 40 years.

  • Multiparity: the risk of having a placenta previa increases with every successive pregnancy.

  • Previous placenta previa:Women who have had previous placenta previa are likely to have it in subsequent pregnancies.

  • Previous Cesarian Section:The incidence of placenta praevia increases with the number of caesarian sections. An article in the American Journal of Obstet and Gynecol, Sept 2005 issue states that 'incidence increased with the number of previous CS: 1.9%, 15.6%, 23.5%, 29.4%, 33.3%, and 50.0% after 0, 1, 2, 3, 4, and 5 previous CS, respectively.

  • Scar on the uterine wall: Any previous surgeries like D&Cs, fibroid removal or abortion or miscarriage can leave a scar in the lower part of the uterus that increases the risks of placenta previa.

  • Multiple gestations: Multiple gestations like twin pregnancy increases the surface area of the placenta requiring more space for implantation.

  • Smoking / cocaine :The blood vessels of the uterus become constricted, decreasing blood supply to the placenta. The placenta implants over a wider area of the uterine wall to increase its own blood supply and may encroach on the lower part of the uterus.

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Signs and Symptoms of Placenta Previa

  • Bleeding: The most important and sometimes the only symptom is bleeding through the vagina. The bleeding is mostly painless, apparently causeless, recurrent and cannot be controlled by medicines. Many patients will complain that they found themselves 'in a pool of blood' on getting up from a sitting or lying down position.

    Bleeding usually occurs after 28 weeks of pregnancy, although it can occur earlier. It starts spontaneously and can stop spontaneously when the patient stays at bed rest.

  • Symptoms of blood loss:If the bleeding has been occurring for some time, the patient may be brought to the hospital with symptoms of blood loss like low blood pressure, or even in a state of shock.

  • On Examination:

    • The uterus is not tender on palpation.
    • The height of the uterus corresponds to the gestational age as calculated from the LMP.
    • Fetal heart rate is usually normal ( if the bleeding is not much).
    • The presenting part of the fetus is high up and can be easily palpated through the abdomen.
    • There may be abnormal presentations like breech or face presentations.

Tests for Placenta Previa

Ultrasonography is the most valuable aid in the diagnosis of placenta previa. With routine ultrasound being done at around 16 weeks of pregnancy at most hospitals, placenta previa can be detected quite early. About 90% of the placenta previas identified before 16 weeks tend to migrate upwards with the enlargment of the uterus. And by the 28th week of pregnancy, they are present in the upper segment of the uterus.

The rest of the 10% of patients with placenta previa should be kept under careful observation till fullterm and provided appropriate treatment.

Treatment 0f Placenta Previa

Treatment depends on the amount of bleeding and the maturity of the fetus.

  • If bleeding is less and the fetus is not mature (less than 34 weeks): Conservative treatment is done by admitting the patient in the hospital, keeping the patient at complete bed rest and under careful observation. Steroids to make the fetal lungs mature are given if the patient is less than 34 weeks of pregnancy.

  • If bleeding is less and the fetus is mature:A cesarian section is done.

  • If bleeding is severe and uncontrollable and the foetus is not mature: If bleeding is severe, the only option is to do a cesarian section to save the life of the mother. With newborn care improving it is possible to save a preterm baby in a hospital with the proper infrastructure.

  • Treatment of symptoms of blood loss: IV fluids, blood transfusion etc. may be needed.

Maternal Complications of Placenta Previa

Maternal complications include hysterectomy, antepartum bleeding, intrapartum and postpartum bleeding, as well as blood transfusion, septicemia, and thrombophlebitis. Maternal mortality (death of the patient) is rare in a well equipped hospital.

Fetal Complications of Placenta Previa

Perinatal mortality (death of the foetus) occurs in around 4% - 8% of patients, mostly due to prematurity.

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