The 'Low Down' on Placenta Previa

Introduction

Hemorrhage is one of the leading causes of pregnancy-related death in the United States. Other causes include cardiac disease, infection, pulmonary embolism, and pregnancy-induced hypertension complications. Most cases of abnormal bleeding during the second and third trimesters of pregnancy are caused by premature separation of the placenta from the uterine wall and abnormal placental implantation. Placenta abruptio is the leading reason for hemorrhage related deaths in pregnancy women and placenta previa is another.

Recall that the placenta and umbilical cord connect the mother and the developing fetus. The placenta and umbilical cord provides oxygen and nutrients to the baby and eliminates carbon dioxide and waste products through a filtering system. A normal placenta is implanted high in the uterus and its surface attaches to the uterus completely. (Fig.1) A potentially life threatening condition for both the mother and the fetus is placenta previa. This is a serious condition that may occur during pregnancy when the placenta abnormally implants in the lower part of the uterus and obstructs the cervical opening to the vagina (birth canal).

Fig. 1: The placenta normally implants high in the uterus.

This article, Part 1 in 3-Part series: "The Low Down on Placenta Previa" will discuss the pathophysiology, incidence, causes and emergency treatment for bleeding caused by placenta previa. Part 2 will discuss Placenta Abruptio and Part 3 will discuss pregnancy induced hypertension and other OB complications.

Placenta previa is always serious and may be life threatening for both the mother and the fetus. The patient can present with varying degrees of hemorrhage. Women who have had good prenatal care will probably know they have placenta previa and those women who have not received consistent prenatal care will not know they have the diagnosis. The challenge the EMS provider faces is that the the true amount of blood being lost may be occult (hidden), difficult to assess due to physiological norms related to pregnancy and/or, in some cases, dismissed by the patient as being a "bloody show" signaling normal labor or they may believe they are experiencing premature labor.

Because of these challenges, the rule for the EMS approach must be: Any pregnant woman who presents with abnormal bleeding (spotting or frank bleeding), with or without pain, must be treated, stabilized and promptly transported for OB evaluation. Unlike first trimester bleeding, second and third trimester bleeding is usually secondary to abnormal placental implantation. Treat these patients like you would treat any hemorrhagic shock patient and keep in mind some of the special considerations for pregnant women. We'll review these considerations later in this article.

Before we delve into the "Low Down about Placenta Previa" we'll present you with two typical prehospital cases of pregnant patients with abnormal bleeding presentations.

Meet The Patients:

Case #1: Abbey Trienan, a 40 year old woman, 29 weeks pregnant, calls 911 after waking from sleep in a pool of blood. She complains of painless bright red vaginal bleeding. This is the patient's fourth pregnancy (G4 P3), and three prior births were by cesarean section. She got up to go to the bathroom and suffered a syncopal episode that lasted about 2 minutes according to her husband who is one scene. She has been on bed rest for a complete placenta previa and is scheduled for a cesarean section when she reaches her 36th week. She presents anxious, scared, and her initial vital signs are: HR: 130/min, RR: 22/min. and BP is 86/50. She is experiencing orthostatic changes. She had been asleep for 5 hours and has no idea how long she has been bleeding, and much of the blood is absorbed into the mattress. On inspection there is a steady trickle of bright red blood coming from the vaginal opening. There are no signs of a presenting fetus or prolapsed umbilical cord. The patient denies contractions or pain.

Case #2: Sheila Dumbrowski, a 37 year old woman, 31 weeks pregnant, calls 911 after noticing some bright red spotting after having intercourse with her husband. She also complains of some regular contractions. She believes she is in "premature labor" because, "I have a bloody show." She admits to irregular prenatal care and her last visit was at the end of her first trimester. She smokes 1 pack per day and she is a G3 P3 (she had one set of twins). Her other pregnancies were uneventful, except she states she was told because she smokes she had, "small babies." She admits, on further questioning that she has had intermittent spotting for the last month, but she also experienced this with her last pregnancy. On inspection there is only some spotting coming from the vaginal opening. There are no signs of a presenting fetus or prolapsed umbilical cord. Despite the very different clinical and historical presentations, both of these women and their unborn children lives are threatened because of placenta previa.

Incidence, causes and risk factors:
The incidence of placenta previa in the United States is approximately 0.5%, or 1 in 200 women. The maternal mortality rate is 0.03%. The retrospective "Maternal Mortality Study" (1979-1986) showed that in 44 maternal deaths, placenta previa was listed as an underlying obstetric condition contributing to death. This resulted in a case fatality rate of .03%. The incidence of maternal death was 1 in 3,300 cases of placenta previa.

The incidence of placenta previa increases with each pregnancy, and it is estimated that the incidence in women who have had 6 or more previous deliveries may be as high as 1 in 20 births. The cause of placenta previa is unknown and may have many factors that contribute to its development. The incidence is doubled in multiple pregnancy (such as twins and triplets). Risk factors include multiparity (previous deliveries), advanced maternal age, previous abortion, possibly smoking, multiple pregnancy, and a previous C-section if the scar is low and close to the vaginal cervix region.

Making the Diagnosis of Placenta Previa

Placenta previa is diagnosed by ultrasound. Because the cervix is very low in the body, a special ultrasound through the vagina (transvaginal ultrasound) is usually needed to obtain ultrasound images of it. There are 3 general types of placenta previa and each comes with their own special considerations. It is very important that if placenta previa is suspected that nothing is inserted in to the vagina that may precipitate hemorrhage. Under no circumstances are internal examinations ever to be conducted in the prehospital setting. Not only is the mother at risk for infection but also for life threatening hemorrhage. In fact, the risk of hemorrhage is so real that even trained physicians will not conduct internal examinations except in the OR where immediate surgical interventions, including Caesarian section are available!

Pathophysiology and Types of Placenta Previa

Placenta previa generally is defined as the implantation of the placenta over or near the internal cervical os (opening to the uterus). The location of placental implantation and how much of the cervical os that is covered can vary. The types of placenta previa are: total, partial, marginal or low-lying placenta previa.

Fig. 2: Total Placenta Previa

Total placenta previa occurs when the cervical os is completely covered by the placenta. Once this condition is diagnosed the baby will absolutely need to be delivered by cesarean Section 4-5 weeks prior to the due date. The mother is often placed on total bed rest until the delivery occurs to decrease the chance of hemorrhage and to allow the baby to develop enough to be able to breathe on its own prior to cesarean section.

Partial placenta previa occurs when the cervical os is partially covered by the placenta. Normal labor and delivery would probably result in hemorrhage as the placenta is damaged by pressure from the baby. Because of the risk, the physician will most likely perform a cesarean section.

Marginal placenta previa occurs when the placenta is at the margin of the internal os The edge of the placenta is very near the opening of the cervix. When the cervix dilates during labor, the placenta may move upward or it may partially block the birth canal. Marginal placenta previa presents a risk of hemorrhage during labor and delivery. While a vaginal delivery is possible in some circumstances, a cesarean section is more likely.

Low-lying placenta previa occurs when the placenta is implanted in the lower uterine segment. In this variation, the edge of the placenta is near, but does not reach, the internal os Most low-lying placentas seen in the first 3 months of pregnancy will go away because as the uterus grows, the placenta moves away from the opening of the uterus. If the placenta does not move up and out of the way, it is called previa.

If there is evidence of contractions during a bleeding episode, medication is often given to stop the contractions. Medication is used even when the contractions are not regular or strong, since only a few contractions may be needed to cause bleeding. Medications that may be administered include a tocolytic such as terbutaline (a beta-2 agonist) or Magnesium Sulfate.

At 4-5 months most cases of placenta previa are diagnosed during routine prenatal care. If the placenta is only a little bit over the cervix, or just very close the cervix, it will usually move away by the due date. If a patient does not have bleeding, and the placenta previa is just diagnosed by ultrasound, there usually does not need to be any changes in the patient's activity level.

Considerations Related to Assessment

The classic presentation of placenta previa is painless bright red vaginal bleeding in the second or third trimester of pregnancy. The bleeding may be heavy or scant. There is often little or no pain. The first sign of placenta previa is bright red bleeding or spotting. Sometimes this bleeding can be confused with a type of light bleeding that often occurs during normal labor, called the bloody show. There is usually no pain, tenderness, uterine contractions, or cramps, although these symptoms may occur. The bleeding may stop and start.

Assessment may reveal signs of compensated or decompensated shock. Remember that some of the classic changes in the pregnant females cardiovascular, respiratory and fluid-volume status may conceal the earliest signs of hypovolemia. Due to the increased fluid volume during the normal pregnant state the mother can lose up to 35% of her blood volume before signs of shock are evident! The uterus can also contain up to 2 liters of blood. Just because external blood loss is absent or minimal, there may be significant occult hemorrhage. In meantime, the brain has told the sympathetic nervous system to instruct the body to vasoconstrict vessels supplying the fetus as a method to compensate for blood loss to the mother.

Resuscitative measures are indicated even if the mother appears stable and is normotensive because the fetus is most likely being be hypoperfused and in serious life threatening shock. Therefore, a high index of suspicion even in the absence of the "classic" signs of shock is warranted. Massive bleeding will threaten both the lives of the mother and the baby. If bleeding is massive, blood transfusion, and probably preterm delivery may be needed.

Attempting to auscultate for fetal heart tones in the field is often a waste of precious time better spent on resuscitation. Special equipment such as a fetoscope or a doppler are often necessary to accurately hear these sounds. While they can be heard with a regular stethoscope it is not easy! Another obstacle we face for hearing fetal heart tones in the prehospital setting is that you need to be able to identify the fetus' position or take several minutes moving the stethoscope around to find the correct area to listen to. Unless you have the proper training, the proper equipment the usefulness of this assessment is marginal. We've already made the assumption of fetal distress. Also, a fetal heart rate that is greater than 160/min. or less than 120/min. is only useful if it is persistent. A trend of abnormal heart rate numbers is more important than one single assessment of heart rate. There are also normal variations that occur in the fetal heart rate that can lead to erroneous assumptions. In rural settings and during prolonged transports these measurements will obviously have more value than in those EMS systems with short transport times. It is recommended they are obtained after transport is begun and after aggressive treatment is initiated.

The physiological changes of pregnancy must be considered and put into context with the emergency situation. The pregnant woman experiences the following physiological changes:

Prehospital Management of Placenta Previa

Let's refer back to our cases for a moment. Abbey Trienan and Sheila Dumbrowski are both suffering from third trimester bleeding. Abbey knows she has been diagnosed with placenta previa and Sheila does not. Abbey is hemodynamically unstable which means that she has already suffered significant blood loss and that her fetus is gravely compromised. On the other hand, Sheila is hemodynamically stable. Remember, based on what we've reviewed in this article that doesn't mean that Sheila isn't hypovolemic and most likely, her fetus is already in shock.

Therefore, the rule for EMS is: Any pregnant woman who presents with abnormal bleeding (spotting or frank bleeding), with or without pain, must be treated, stabilized and promptly transported for OB evaluation. Unlike first trimester bleeding, second and third trimester bleeding is usually secondary to abnormal placental implantation. Treat these patients like you would treat any hemorrhagic shock patient, limit field time, and keep in mind some of the special considerations for pregnant women. Fluid resuscitation and treatment based on a high index of suspicion are warranted.

After assessing your patient, provide any airway, ventilatory and circulatory support as needed. In general, both Abbey and Sheila need to receive oxygen by non-rebreather face mask and you should assume that both women are susceptible to vena cava syndrome (compression of the abdominal aorta and vena cava) and should be placed in the left lateral recumbent position. Since both women are well into their pregnancies, vena cava syndrome can be prevented and simply positioning the patient on her left side will optimize blood flow to both the fetus and mother. Begin transport immediately and enroute start a large bore IV and begin fluid resuscitation with an isotonic crystalloid IV fluid such as Normal Saline. Remember that even in the normotensive pregnant patient the fetus is still at risk and physiological body changes can mask the classic signs of shock we expect to see in the non-pregnant patient.

Notify the ED of the patient's parity, gravidity, history of any past cesarean section, maternal lifestyle (ETOH, smoking, etc.), LMP, due date, uterine size by fundal height, past medical history, medications taken, present condition and treatment being administered. This will allow the ED to alert the Labor & Delivery team so they may be prepared to serve this patient's special needs. To help estimate blood loss you should apply a fresh perineal pad to so that a "pad count" can begin. Perineal pads will typically become saturated with about 75 cc of blood. The number of saturated pads in one hour (or in 30 minutes) can yield important information about the rate of blood loss.

In-Hospital Management of Placenta Previa

In hospital management strategies attempt to balance the risks of maternal interventions against the risks of prematurity to the baby. Advances in medical care of previously diagnosed placenta previa include blood banking, anesthesia management, use of corticosteriods (to stimulate the fetus to develop surfactant quicker), and neonatal surfactant have improved maternal and neonatal outcome. A maternal mortality of 0.03% (1 in 3,300) and a neonatal mortality of 4-8% is the best estimate of poor outcome. The primary factors affecting outcome are blood loss, prematurity of the fetus, and placental invasion (placenta grows into the uterine tissue resulting in the need for surgical removal). Cesarean delivery is required and if placental invasion is present, a hysterectomy is often performed. Careful planning and delivery management with a multidisciplinary team may be required to improve outcome from women suffering from placenta previa.

The women who present with no previous diagnosis of placenta previa have a greater risk of a negative outcome. The emergency management of placenta previa will follow general management of send or third trimester bleeding guidelines. Routine treatment will include oxygen, positioning, fluid resuscitation, possible blood transfusions, tocolytic therapy, or even immediate cesarean section.

Coming next edition: Part Two: The Low Down on Placenta Abruptio

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References:

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