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Causes and symptoms
- having abnormalities of the uterus
- being older in age
- having had other babies
- having a prior delivery by cesarean section
- smoking cigarettes
placenta[plah-sen´tah] (pl. placentas, placen´tae) (L.)
In anatomic nomenclature the placenta consists of a uterine and a fetal portion. The chorion, the superficial or fetal portion, is surfaced by a smooth, shining membrane continuous with the sheath of the umbilical cord (amnion). The deep, or uterine, portion is divided by deep sulci into lobes of irregular outline and extent (the cotyledons). Over the maternal surface of the placenta is stretched a delicate, transparent membrane of fetal origin. Around the periphery of the placenta is a large vein (the marginal sinus), which returns a part of the maternal blood from the organ.
The major function of the placenta is to allow diffusion of nutrients from the mother's blood into the fetus's blood and diffusion of waste products from the fetus back to the mother. This two-way exchange takes place across the placental membrane, which is semipermeable; that is, it acts as a selective filter, allowing some materials to pass through and holding back others.
In the early months of pregnancy the placenta acts as a nutrient storehouse and helps to process some of the food substances that nourish the fetus. Later, as the fetus grows and develops, these metabolic functions of the placenta are gradually taken on by the fetal liver.
The placenta secretes both estrogens and progesterone. After birth of the infant the placenta is cast off from the uterus and expelled via the birth canal.
With the onset of any contractions and cervical dilation, or when the cervix begins to dilate at the onset of labor and the upper and lower uterine segments differentiate, the placenta is stretched and pulled from the uterine wall, producing bleeding. The bleeding usually is abrupt and painless and may stop on its own. However, if it continues it can be life-threatening for the mother since it is maternal blood that is being lost. The life of the fetus is in jeopardy because of anoxia resulting from separation of the placenta from its blood supply.
Diagnosis can be established by ultrasonography or radiologic placentography. Once diagnosis is made, treatment will depend on the gestational age of the fetus and the percentage of placenta covering the cervical os. Cesarean delivery is recommended if 30 per cent or more of the opening is obstructed by the placenta. If there is minimal bleeding that stops on its own, the fetus is not in distress, and if the gestational age is such that continuing the pregnancy is necessary for delivery of a viable fetus, the pregnancy may be continued under careful monitoring in the hospital, or at home if the mother is able to stay in bed. However, if the life of the mother or fetus is threatened by continued and excessive bleeding, delivery is indicated.
Vaginal examinations are carried out in an operating room so that if hemorrhage does occur as a result of manipulation of the uterus, a cesarean section can be done immediately to remove the placenta, stop the bleeding, and deliver the child safely.
Postpartal hemorrhage and infection are more likely in women who have had placenta previa. Placement of the placenta in the lower segment predisposes to more bleeding because that portion of the uterus does not contract as forcefully as the upper segment. Additionally, the misplaced placenta has enlarged its bed to compensate for its poor location, so that there is a larger denuded area after delivery of the placenta. The same denuded area is also more susceptible to infection because it is located near the cervical opening where infectious organisms may enter.
Vaginal bleeding during pregnancy or labor is frightening for the mother. She will need reassurance and frequent explanations of what is happening to her throughout the period of monitoring and delivery. Some emotional stress can be alleviated by encouraging the mother to be aware of fetal movements and allowing her to listen to normal fetal heart sounds.
placenta previaObstetrics A condition in which the placenta implants in the lower uterus and obstructs the birth canal Etiology Scarred endometrium, a large placenta, abnormal placentation Incidence ±1 in 200 births; 1 in 20 with multiparas, doubled in multiparas Risk factors Multiparity, multiple pregnancy, prior C-section if scar is low and close to the cervix region
pla·cen·ta pre·vi·a(plă-sen'tă prē'vē-ă)
Synonym(s): placental presentation.
|Mean LOS:||4.8 days|
|Description:||SURGICAL: Cesarean Section With CC or Major CC|
|Mean LOS:||3.3 days|
|Description:||MEDICAL: Vaginal Delivery With Complicating Diagnoses|
Placenta previa occurs in 1.9 per 1,000 primiparous singleton pregnancies and 3.9 per 1,000 multiparous singleton pregnancies. Normally, the placenta implants in the body (upper portion) of the uterus. Implantation allows for delivery of the infant before the delivery of the placenta. With placenta previa, the placenta is implanted in the lower uterine segment over or near the internal os of the cervix. As the uterus contracts and the cervix begins to efface and dilate, the villi of the placenta begin to tear away from the uterine wall and bright red, painless, vaginal bleeding occurs. The bleeding is facilitated by the poor ability of the myometrial fibers of the lower uterine segment to contract and constrict the torn vessels. Bleeding can occur antepartally or intrapartally. Hemorrhage from the placental site may continue into the postpartum period because the lower uterine segment contracts poorly, contrasted with the fundus and body of the uterus. Placenta previa is classified in four ways depending on the degree of placental encroachment on the cervical os (Box 1).
The degree of the previa depends largely on the cervical dilation. For example, a marginal previa at 2 cm may become a partial previa at 8 cm because the dilating cervix uncovers the placenta. Sometimes, a placenta may correct itself, especially if it is low lying; as the uterus enlarges, the placenta moves cephalad. Depending on the amount of blood loss and gestational age of the fetus, placenta previa may be life-threatening to both the mother and the fetus.Classification of Placenta Previa
- Low Lying
- The placenta implants in the lower uterine segment but does not reach the cervical os; often this type of placenta previa moves upward as the pregnancy progresses, eliminating bleeding complications later.
- The edge of the placenta is at the edge of the internal os; the mother may be able to deliver vaginally.
- The placenta partially covers the cervical os; as the pregnancy progresses and the cervix begins to efface and dilate, bleeding occurs.
- The placenta covers the entire cervical os; this usually requires an emergency cesarean section.
The cause of placenta previa is unknown, but it is more common in women who have a history of uterine surgeries (cesarean sections, dilation and curettage), infections with endometritis, and a previous placenta previa. It is also more common in women who currently have a multiple gestation with a large placenta. Smoking is also a contributing factor.
No clear genetic contributions to susceptibility have been defined.
Gender, ethnic/racial, and life span considerations
Placenta previa is more common in women of advanced maternal age (over 35) and in patients with multiparity; it occurs in approximately 1 of 1,500 deliveries of women who are 19 and 1 in 100 deliveries of women over 35. The incidence of placenta previa has increased over the past 30 years; this increase is attributed to the shift in older women having infants. Overall incidence is 1 in 200 deliveries; risk for recurrence may be as high as 10% to 15%. The maternal mortality rate from previas is 0.3%. Ethnicity and race have no established effects on the risk for placenta previa.
Global health considerations
While no global data are available, placenta privia occurs around the world.
Although many women who develop placenta previa have an unremarkable obstetric or gynecologic history, some have had previous uterine surgeries or infections. The prenatal course of the current pregnancy is often uneventful until the patient experiences a bout of bright red, painless bleeding. Question the patient as to the onset and amount of bleeding first noticed. The initial bleeding in placenta previa is often scant because few uterine sinuses are exposed.
The classic sign of placenta previa is painless, bright red bleeding; assess the amount and character of blood loss. Most often this bleeding occurs between 28 and 34 weeks when the lower uterine segment thins and the low implantation site is disrupted, but it may occur as early as 16 to 24 weeks. If heavy bleeding occurs at this point, there is over a 50% chance of pregnancy loss. With a marginal or low-lying placenta previa, the bleeding may not start until the patient is in labor. Assess the uterus for contractions; unless the patient is in labor, the uterus is relaxed and nontender. A vaginal examination should not be performed because even the gentlest examination can cause immediate hemorrhage.
Check the vital signs; note any symptoms of hypovolemic shock (restlessness; agitation; increased pulse; delayed capillary blanching; increased respirations; pallor; cool, clammy skin; hypotension; and oliguria). Monitor the baseline fetal heart rate and the presence or absence of accelerations, decelerations, and variability in the electronic fetal monitoring (EFM).
Ask the patient if she feels the fetus move. Assess the fetal position and presentation by using Leopold’s maneuvers. Monitor the patient’s contraction status and palpate the fundus to determine the intensity of contractions. View the fetal monitor strip to assess the frequency and duration of the contractions; more often, the uterus is soft and nontender, unless the patient is in labor. Throughout the patient’s hospitalization, continue to monitor for signs of hypovolemic shock and the amount and character of bleeding. Maintain continuous EFM until bleeding ceases; then, if hospital policy permits, monitor the fetus for 30 minutes every 4 hours.
The heavy, bright red bleeding that often accompanies placenta previa is anxiety producing for the mother and significant others. The patient is concerned not only for herself, but also for the well-being of the infant. Determine the patient’s support system because many of these patients have been on complete bedrest for an extended period of time. Assess the effect of prolonged bedrest on the patient’s job, child care, interpersonal, financial, and social responsibilities.
General Comments: Vaginal examinations are contraindicated for a pregnant patient who is bleeding until a previa is ruled out by ultrasound visualization.
|Test||Normal Result||Abnormality With Condition||Explanation|
|Transvaginal ultrasound (preferred); transabdominal ultrasound is also done||Placental implantation visualized in fundus of uterus||Placental implantation visualized in lower uterine segment||Visualization of placenta determines location and can rule out other causes of bleeding (e.g., abruption, cervical lesion, excessive show)|
|Red blood cell count||4–5.4 mL/mm3||Decreases several hours after significant blood loss has occurred||Active bleeding causes decrease|
|Hemoglobin||12–16 g/dL||Decreases several hours after significant blood loss has occurred||Active bleeding causes decrease|
|Hematocrit||37%–47%||Decreases several hours after significant blood loss has occurred||Active bleeding causes decrease|
Other Tests: Blood type and crossmatch; coagulation studies if bleeding is excessive
Primary nursing diagnosis
DiagnosisFluid volume deficit related to blood loss
OutcomesFluid balance; Hydration; Circulation status
InterventionsBleeding reduction; Blood product administration; Intravenous therapy; Shock management
Planning and implementation
Management of a patient with placenta previa depends on the admission status of the mother and the fetus, the amount of blood loss, the likelihood that the bleeding will subside on its own, and the gestational age of the fetus. If both the mother and the fetus are stable and the fetus is immature (less than 37 weeks), delivery may be put off and an intravenous (IV) infusion started with lactated Ringer’s solution. In addition, the patient is maintained on bedrest with continuous EFM. Closely monitor the fetal heart rate. If any signs of fetal distress are noted (flat variability, late decelerations, bradycardia, tachycardia), turn the patient to her left side, increase the rate of IV infusion, administer oxygen via face mask at 10 L/min, and notify the physician. Once the bleeding has ceased for 24 to 48 hours, the patient may be discharged to her home on bedrest before delivery. This conservative treatment gives the preterm fetus time to mature. If the patient is in labor and a marginal placenta previa is present, the physician allows her to labor and deliver vaginally, with careful surveillance of maternal and fetal status throughout the labor. Postpartum, the patient will require oxytocics to prevent hemorrhaging, owing to the poor ability of the lower uterine segment to contract.
If fetal distress is present or if the patient has lost a significant amount of blood, an immediate cesarean section and, possibly, blood transfusions are indicated. If the patient delivers (vaginally or by cesarean), monitor her for postpartum hemorrhage because contraction of the lower uterine segment is sometimes not effective in compressing the uterine vessels that are exposed at the placental site. Although medication is not given to treat a previa, pharmacologic treatment may be indicated to stop preterm labor (if it is occurring and if bleeding is under control), enhance fetal lung maturity if delivery is expected prematurely, or prevent Rh disease, if the patient delivers. Women with placenta previa have an increased chance of complications and hysterectomy.
|Medication or Drug Class||Dosage||Description||Rationale|
|Magnesium sulfate||4–6 g IV loading dose, 1–4 g/hr of IV maintenance||Central nervous system depressant||Effective tocolytic, has fewer side effects than beta-adrenergic drugs; administered only if bleeding is under control and preterm labor is evident|
|Betamethasone (Celestone)||12 mg IM q 24 hr × 2 doses||Glucocorticoid||Hastens fetal lung maturity; given if delivery is anticipated between 24 and 34 wk|
|RhD immunoglobulin (RhoGAM)||120 mcg (prepared by blood bank)||Immune serum||Prevents Rh isoimmunizations in future pregnancies; given if mother is Rh-negative and infant is Rh-positive|
If the patient is actively bleeding and mother and fetus are stable, maintain the patient on bedrest in the lateral position (preferably left lateral) to maximize venous return and placental perfusion. Because the patient may be on bedrest for an extended period of time, comfort can be increased with back rubs and positioning with pillows. Provide diversional activities and emotional support. The nurse should make every attempt to explain the condition, treatment, and potential outcomes to the patient. Often, if a preterm delivery is unavoidable, a special care nursery nurse comes in and discusses what the mother can expect to happen to her infant on admission to the neonatal intensive care unit.
Evidence-Based Practice and Health Policy
Rosenberg, T., Pariente, G., Sergienko, R., Wiznitzer, A., & Sheiner, E. (2011). Critical analysis of risk factors and outcome of placenta previa. Archives of Gynecology and Obstetrics, 284(1), 47–51.
- Investigators conducted a retrospective population-based review of 185,476 births in order to examine the risk profiles of women who experienced placenta previa. Seven hundred seventy-one births (0.42% of deliveries) were complicated by placenta previa in this study.
- When compared with the control population, a greater proportion of women with placenta previa experienced adverse outcomes, including postpartum hemorrhage (1.4% versus 0.5%; p = 0.001), hysterectomy (5.3% versus 0.04%; p < 0.001), intrauterine growth restriction (3.6% versus 2.1%; p = 0.003), birth to infants with Apgar scores < 7 at 1 and 5 minutes (25.3% versus 5.9% and 7.1% versus 2.6%, respectively; p < 0.001), and perinatal mortality (6.6% versus 1.3%; p < 0.001).
- Placenta previa was 1.76 times more likely among women who had a prior cesarean birth (95% CI, 1.48 to 2.09; p < 0.001) and 1.97 times more likely among women with a history of infertility treatments (95% CI, 1.45 to 2.66; p < 0.001).
- Amount and character of blood loss; vital signs; presence or absence of signs of hypovolemic shock; fetal heart rate baseline, variability, and presence or absence of accelerations or decelerations; intake and output
- Frequency, intensity, and duration of contractions
- Emotional well-being; patient’s response to high-risk situation
Discharge and home healthcare guidelines
If the patient is discharged undelivered, provide the following instructions:
- Notify the physician of any vaginal bleeding, spontaneous rupture of membranes, decreased fetal movement, or regular labor contractions.
- Maintain continuous bedrest with bathroom privileges.
- Avoid the supine position; use the lateral or semi-Fowler’s position.
- Abstain from sexual intercourse.
- Be sure to have the means to reach the hospital at all times.