placenta previa

Placenta Previa

Definition

Placenta previa is a condition that occurs during pregnancy when the placenta is abnormally placed, and partially or totally covers the cervix.

Description

The uterus is the muscular organ that contains the developing baby during pregnancy. The lowest segment of the uterus is a narrowed portion called the cervix. This cervix has an opening (the os) that leads into the vagina, or birth canal. The placenta is the organ that attaches to the wall of the uterus during pregnancy. The placenta allows nutrients and oxygen from the mother's blood circulation to pass into the developing baby (the fetus) via the umbilical cord.During labor, the muscles of the uterus contract repeatedly. This allows the cervix to begin to grow thinner (called effacement) and more open (dilatation). Eventually, the cervix will become completely effaced and dilated, and the baby can leave the uterus and enter the birth canal. Under normal circumstances, the baby will emerge through the mother's vagina during birth.In placenta previa, the placenta develops in an abnormal location. Normally, the placenta should develop relatively high up in the uterus, on the front or back wall. In about one in 200 births, the placenta will be located low in the uterus, partially or totally covering the os. This causes particular problems in late pregnancy, when the lower part of the uterus begins to take on a new formation in preparation for delivery. As the cervix begins to efface and dilate, the attachments of the placenta to the uterus are damaged, resulting in bleeding.

Causes and symptoms

While the actual cause of placenta previa is unknown, certain factors increase the risk of a woman developing the condition. These factors include:

having abnormalities of the uterus
being older in age
having had other babies
having a prior delivery by cesarean section
smoking cigarettes

When a pregnancy involves more than one baby (twins, triplets, etc.), the placenta will be considerably larger than for a single pregnancy. This also increases the chance of placenta previa.Placenta previa may cause a number of problems. It is thought to be responsible for about 5% of all miscarriages. It frequently causes very light bleeding (spotting) early in pregnancy. Sometime after 28 weeks of pregnancy (most pregnancies last about 40 weeks), placenta previa can cause episodes of significant bleeding. Usually, the bleeding occurs suddenly and is bright red. The woman rarely experiences any accompanying pain, although about 10% of the time the placenta may begin separating from the uterine wall (called abruptio placentae), resulting in pain. The bleeding usually stops on its own. About 25% of such patients will go into labor within the next several days. Sometimes, placenta previa does not cause bleeding until labor has already begun.Placenta previa puts both the mother and the fetus at high risk. The mother is at risk of severe and uncontrollable bleeding (hemorrhage), with dangerous blood loss. If the mother's bleeding is quite severe, this puts the fetus at risk of becoming oxygen deprived. The fetus' only source of oxygen is the mother's blood. The mother's blood loss, coupled with certain changes that take place in response to that blood loss, decreases the amount of blood going to the placenta, and ultimately to the fetus. Furthermore, placenta previa increases the risk of preterm labor, and the possibility that the baby will be delivered prematurely.

Diagnosis

Diagnosis of placenta previa is suspected whenever bright red, painless vaginal bleeding occurs during the course of a pregnancy. The diagnosis can be confirmed by performing an ultrasound examination. This will allow the location of the placenta to be evaluated.While many conditions during pregnancy require a pelvic examination, in which the health care provider's fingers are inserted into the patient's vagina, such an examination should never be performed if there is any suspicion of placenta previa. Such an examination can disturb the already susceptible placenta, resulting in hemorrhage.Sometimes placenta previa is found early in a pregnancy, during an ultrasound examination performed for another reason. In these cases, it is wise to have a repeat ultrasound performed later in pregnancy (during the last third of the pregnancy, called the third trimester). A large percentage of these women will have a low-lying placenta, but not a true placenta previa where some or all of the os is covered.

Treatment

Treatment depends on how far along in the pregnancy the bleeding occurs. When the pregnancy is less than 36 weeks along, the fetus is not sufficiently developed to allow delivery without a high risk of complications. Therefore, a woman with placenta previa is treated with bed rest, blood transfusions as necessary, and medications to prevent labor. After 36 weeks, the baby can be delivered via cesarean section. This is almost always the preferred method of delivery in order to avoid further bleeding from the low-lying placenta.

Prognosis

In cases of placenta previa, the prognosis for the mother is very good. However, there is a 15-20% chance the infant will not survive. This is 10 times the death rate associated with normal pregnancies. About 60% of these deaths occur because the baby delivered was too premature to survive.

Prevention

There are no known ways to insure the appropriate placement of the placenta in the uterus. However, careful treatment of the problem can result in the best chance for a good outcome for both mother and baby.

Resources

Organizations

American College of Obstetricians and Gynecologists. 409 12th Street, S.W., P.O. Box 96920, Wasington, DC 20090-6920.

Key terms

Cesarean section — Delivery of a baby through an incision in the mother's abdomen instead of through the vagina.Labor — The process during which the uterus contracts, and the cervix opens to allow the passage of a baby into the vagina.Placenta — The organ that provides oxygen and nutrition from the mother to the baby during pregnancy. The placenta is attached to the wall of the uterus and leads to the baby via the umbilical cord.Umbilical cord — The blood vessels that allow the developing baby to receive nutrition and oxygen from its mother; the blood vessels also eliminate the baby's waste products. One end of the umbilical cord is attached to the placenta and the other end is attached to the baby's belly button (umbilicus).Vagina — The birth canal; the passage from the cervix of the uterus to the opening leading outside of a woman's body.

placenta

[plah-sen´tah] (pl. placentas, placen´tae) (L.) an organ characteristic of true mammals during pregnancy, joining mother and offspring, providing endocrine secretion and selective exchange of soluble bloodborne substances through apposition of uterine and trophoblastic vascularized parts. See also afterbirth. adj., adj placen´tal.
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.placenta accre´ta one abnormally adherent to the myometrium, with partial or complete absence of the decidua basalis.battledore placenta one with the umbilical cord inserted at the edge.placenta circumvalla´ta one encircled with a dense, raised, white nodular ring, the attached membranes being doubled back over the edge of the placenta.placenta fenestra´ta one that has spots where placental tissue is lacking.placenta incre´ta placenta accreta with penetration of the myometrium.placenta membrana´cea one that is abnormally thin and spread over an unusually large area of the myometrium.placenta percre´ta placenta accreta with invasion of the myometrium to the peritoneal covering, sometimes causing rupture of the uterus.placenta pre´via low implantation of the placenta so that it partially or completely covers the cervical os. Percentages are used to designate the amount of obstruction; e.g., 100 per cent is total placenta previa, and 50 per cent indicates that about half the opening is obstructed. The condition occurs with greater frequency in women who have had multiple pregnancies or are over 35. The exact cause is not known.
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.Patient Care. Premature separation of the placenta is an emergency. The maternal signs are monitored every 15 minutes and blood loss is evaluated. Fetal heart tones also are monitored to detect fetal distress. The amount of bleeding is estimated and documented. Oxygen equipment should be at hand in the event signs of fetal distress indicate anoxia.
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 reflex´a one in which the margin is thickened, appearing to turn back on itself.placenta spu´ria an accessory portion without blood vessels connecting it with the main placenta.placenta succenturia´ta an accessory portion with an artery and a vein connecting it with the main placenta.

pla·cen·ta pre·vi·a

the condition in which the placenta is implanted in the lower segment of the uterus, extending to the margin of the internal os of the uterus or partially or completely obstructing the os. Synonym(s): placental presentation

placenta previa

Obstetrics 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) The condition in which the placenta is implanted in the lower segment of the uterus, extending to the margin of the internal os of the cervix or partially or completely obstructing the os.
Synonym(s): placental presentation.

Placenta Previa

DRG Category:	765
Mean LOS:	4.8 days
Description:	SURGICAL: Cesarean Section With CC or Major CC
DRG Category:	774
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

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.

Causes

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.

Genetic considerations

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.

Assessment

History

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.

Physical examination

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.

Psychosocial

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.

Diagnostic highlights

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

Diagnosis

Fluid volume deficit related to blood loss

Outcomes

Fluid balance; Hydration; Circulation status

Interventions

Bleeding reduction; Blood product administration; Intravenous therapy; Shock management

Planning and implementation

Collaborative

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.

Pharmacologic highlights

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

Independent

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).

Documentation guidelines

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.

placenta previa

placenta previa

placenta previa

placenta previa

Placenta Previa

Definition

Description

Causes and symptoms

Diagnosis

Treatment

Prognosis

Prevention

Resources

Organizations

Key terms

placenta

pla·cen·ta pre·vi·a

placenta previa

pla·cen·ta pre·vi·a

Placenta Previa

Causes

Genetic considerations

Gender, ethnic/racial, and life span considerations

Global health considerations

Assessment

History

Physical examination

Psychosocial

Diagnostic highlights

Primary nursing diagnosis

Diagnosis

Outcomes

Interventions

Planning and implementation

Collaborative

Pharmacologic highlights

Independent

Evidence-Based Practice and Health Policy

Documentation guidelines

Discharge and home healthcare guidelines

placenta previa

Words related to placenta previa

noun pregnancy in which the placenta is implanted in the lower part of the uterus (instead of the upper part)

Related Words