Placenta Previa

What is Placenta Previa?
Placenta Previa is when your placenta moves and covers part or all of the cervix. It can also be known as a low lying placenta. This is not a common pregnancy complication as about 1 in every 250 pregnancies may have placenta previa. Placenta previa can cause severe bleeding during pregnancy. An uncontrolled hemorrhage may even put the mother and baby’s life in danger, and should this happen the baby will be delivered by caesarean section, even if the baby's due date is weeks away. There are actually three types of previa:

1. Complete previa : occurs when the cervical os is completely covered
2. Partial previa : involves only a portion of the cervix being covered by the placenta
3. Marginal previa : extends just to the edge of the cervix

Signs and Symptoms
Diagnosing a previa is usually made when there is painless bleeding during the third trimester. If you are bleeding, it is unwise to do a vaginal exam until an ultrasound has ruled out a placenta previa. Bleeding from your vagina during the second or third trimester may be the first sign of placenta previa, although in many cases there are no signs at all. However, there is a 10% false positive diagnosis rate, usually because of the bladder being overfull. There is also a 7% false negative rate, typically caused from missing the previa that is located behind the baby's head. Other reasons to suspect a previa include:

  • premature contractions
  • abnormal presentation (breech, transverse, etc.)
  • uterus measuring larger than it should according to dates

Risk Factors
There are a few predisposing factors. The following can increase your risk for placenta previa:

  • advanced maternal age
  • increased parity (number of pregnancies)
  • previous uterine surgery (regardless of incision type)

Treatment of placenta previa depends on how far along your pregnancy is and how much bleeding you are experiencing. If it is diagnosed after the 20th week of your pregnancy, and you are not experiencing any bleeding, you may be simply asked to cut back on your activities, and increase the amount of time you spend in bed. You should, however, be alert for any bleeding in which case you will be put on bed rest, be told to refrain from sexual intercourse and be monitored more closely by your practitioner. This is because up to 90% of complete previas will resolve by term. However, if you are found to be bleeding you may be hospitalized until both you and your baby are stabilized, and even then you may be told to stay in bed as much as possible until the baby is ready to be delivered.

If bleeding is very heavy, transfusions may be necessary until the fetus is mature enough for delivery. Steroid injections may be used to speed fetal lung maturity. Ultimately, the goal is to try to keep the pregnancy going until at least 36 weeks, at which point the baby may be delivered by cesarean to reduce the risk of massive hemorrhage.

True placenta previa at term is very serious. Complications for the baby include:

  • problems for the baby, secondary to acute blood loss
  • intrauterine growth retardation due to poor placental perfusion
  • increased incidence of congenital anomalies

Risks for Mother Include:

  • life-threatening hemorrhage
  • cesarean delivery
  • increased risk of postpartum hemorrhage
  • increased risk of placenta accrete; placenta accrete is where the placenta attaches directly to the uterine muscle

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