The average blood loss at the time of delivery is approximately 500 cc during a vaginal delivery and approximately 1,000 cc during a cesarean section. Excessive blood loss or "postpartum hemorrhage" complicates approximately 4% of vaginal deliveries and 6-7% of cesarean sections.
Common causes of hemorrhage around the time of delivery include uterine atony, vaginal or cervical tears, retained fragments of placenta, placenta previa, placenta accreta and uterine rupture. Hereditary abnormalities in blood clotting may cause hemorrhage as well.
Dr. Miller is Associate Professor of Clinical Obstetrics and Gynecology at the University of Southern California School of Medicine.
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Uterine atony is a term used to describe the failure of the uterine muscle to contract normally following delivery of the baby and placenta. This condition is responsible for up to 90% of all cases of postpartum hemorrhage. Separation of the placenta from the wall of the uterus results in shearing of the mother's blood vessels that previously supplied blood to the placenta. Normally, bleeding from these severed vessels is stopped by contraction of the uterus and compression of the vessels. If uterine contraction is not adequate, bleeding can continue. At times, the uterus is prevented from contracting effectively by fragments of placenta that remain in the uterus after delivery or by benign growths of uterine muscle within the uterine wall known as fibroids. In these cases, the term "atony" usually is not applied. In most cases, the uterine muscle simply fails to contract adequately.
Many factors can cause the uterus to fail to contract after delivery.
These are summarized in
Table 1. Factors associated with uterine atony
|Prolonged labor ||
|General anesthetics (halothane) ||
|Multiple gestation ||
In patients with risk factors for uterine atony, excessive bleeding at the time of delivery should be anticipated and, whenever possible, preparations should be made before delivery. General precautions include establishing at least one large-bore intravenous line, ensuring the availability of uterine contraction medications (oxytocin, methylergonovine, prostaglandins) and confirming that appropriate nursing and anesthesia personnel are available and aware of the possibility of postpartum hemorrhage. In selected high-risk patients, it may be appropriate to notify the blood bank of the potential need for blood transfusion. After delivery, uterine atony is detected when there is excessive bleeding and a large, relaxed uterus. Your doctor may perform an examination to be certain that there are no bleeding tears of the cervix or the vagina and that all fragments of placenta have been removed from the uterus. If vaginal or cervical lacerations are found, they should be repaired.
Massaging the uterus often causes the uterus to contract and oxytocin usually is given intravenously to stimulate uterine contractions. The doctor may compress the uterus between one hand in the vagina and the other on the abdomen.
If this approach is not successful, medications such as methylergonovine or prostaglandin may be used. If atony persists despite these maneuvers, surgery may be necessary.
The objective of surgery is to control the bleeding as rapidly as possible. Often, this can be accomplished by clamping the blood vessels that supply the uterus. If successful, this procedure should not affect future pregnancies.
In some settings, interventional radiology may provide another alternative. Using X-ray guidance, small catheters can be placed through the blood vessels in the leg and into the blood vessels supplying the uterus. The blood vessels then can be injected with gelatin sponge particles or spring coils to obstruct blood flow to the uterus. Although successful control of hemorrhage has been reported with this technique, it may not be available in emergency situations. If conservative measures fail to control the bleeding, hysterectomy may be necessary. Severe bleeding may necessitate blood transfusion.
Prompt recognition and intervention are the cornerstones of successful management of uterine atony. Alternate sources of bleeding, such as vaginal or cervical lacerations or retained placental fragments, must be excluded. Blood and fluid must be replaced as needed. Conservative measures for control of bleeding include uterine massage, uterine pressure and administration of medications to stimulate uterine contractions (oxytocin, methylergonovine, prostaglandins). Surgery may be necessary to occlude the blood supply to the uterus. If this is not successful, hysterectomy may be required.
Placenta previa is a condition in which the placenta attaches to the uterine wall in the lower portion of the uterus and covers all or part of the cervix. Although the cause of placenta previa is unknown, the risk factors listed in Table 2 suggest that some cases may be caused by previous scarring of the uterine wall.
Table 2. Risk factors for placenta previa
- Previous cesarean section
- Advanced maternal age
- Multiple gestation
- Erythroblastosis fetalis
The incidence of placenta previa at term is approximately 1 in 200. The three categories of the disorder are defined below. An additional form of abnormal placentation is the low-lying placenta, in which the placental edge extends to within 2 cm of the cervix or is within reach of the examining finger introduced through the cervix.
Marginal placenta previa: Placenta extends to the margin of the internal cervical os
Partial placenta previa: Placenta partially covers internal cervical os
Complete placenta previa: Placenta completely covers internal cervical os
Placenta previa is much more common in early pregnancy than at term. During routine second-trimester ultrasound, the placenta is observed to cover the cervix in 5 to 20% of pregnancies. However, because of the growth of the uterus throughout pregnancy, more than 90% of early placenta previas convert to a normal location by the time of delivery. Conversion to normal location is less common in centrally-located complete placenta previa.
Placenta previa classically is characterized by painless vaginal bleeding in the late second or third trimester. However, uterine pain and/or contractions do not exclude the diagnosis in a woman who presents with vaginal bleeding. In many cases, placenta previa remains asymptomatic throughout pregnancy.
Historically, placenta previa has been associated with increased maternal and perinatal morbidity and mortality. Preterm delivery and complications of prematurity are the most common sources of perinatal morbidity, occurring in nearly two-thirds of cases. Abnormal fetal presentation is observed in up to 30% of cases. Placental separation and bleeding may cause the newborn to be anemic. Hemorrhage and complications of cesarean delivery are the most common causes of maternal morbidity. Blood transfusions are necessary is one-third to one-half of cases.
In addition, 9 to 10% of cases of placenta previa are associated with placenta accreta, an abnormally firm attachment of the placenta to the wall of the uterus. Placenta accreta prevents the placenta from separating from the uterine wall at the time of delivery and can cause severe bleeding that often necessitates hysterectomy. Placenta accreta is particularly common in women with placenta previa and one or more previous cesarean sections and may complicate one-third to one-half of all such cases. More than 50% of patients with placenta accreta require blood transfusion.
Many cases of placenta previa are diagnosed by routine ultrasound. In other cases, the initial diagnosis is made when the patient comes to the hospital with vaginal bleeding during the second half of pregnancy. Ultrasound may confirm the suspicion of placenta previa. When adequate visualization of the relationship between the placenta and the cervix is not possible with abdominal ultrasound, a transvaginal ultrasound may be helpful. Careful transvaginal sonography does not appear to increase the risk of bleeding in placenta previa.
Placenta previa diagnosed by routine second-trimester ultrasound is managed expectantly. The likelihood of spontaneous resolution is greater than 90%. Strenuous activity may provoke bleeding and should be avoided. Placental location should be reevaluated at 28 to 30 weeks. If placenta previa is still present, the same precautions should be followed. If placenta previa persists beyond 32 to 34 weeks, resolution by term is uncommon. Cesarean section usually is scheduled at a gestational age that will maximize the likelihood of fetal maturity and minimize the risk of hemorrhage that may result from the normal onset of uterine contractions. In patients who are not experiencing bleeding, amniocentesis may be performed at 34 to 36 weeks to assess fetal lung maturity. If the baby's lungs are mature, delivery usually is indicated. Otherwise, management is individualized based on the condition of the mother and the baby. Waiting beyond 37 weeks is not likely to benefit for the fetus or mother.
In the case of bleeding placenta previa, the mother's interest is best served by immediate delivery. However, the decision also must take into account the interests of the fetus. In all cases of active hemorrhage, the primary consideration is to ensure the mother is stable and not in jeopardy. Large IV lines usually are established, fluids are administered and blood availability is confirmed. Blood transfusion often is necessary when active bleeding is present.
The condition of the baby usually is assessed with continuous electronic fetal heart rate (FHR) monitoring, and ultrasound may be ordered to estimate the gestational age and fetal weight. Medications such as magnesium sulfate, terbutaline, ritodrine, nifedipine or indomethacin may be used to stop uterine contractions.
If any of the following are present, immediate cesarean section usually is necessary:
- Deteriorating condition of the mother
- Persistent heavy bleeding
- Gestational age > 36 weeks
- Estimated fetal weight > 2500 gm
- Fetal distress in a viable fetus
- Contractions that do not respond to medication
Placenta accreta is a potential complication in all women with placenta previa, particularly those with previous cesarean sections. Other risk factors for placenta accreta include maternal age of 35 or more, multiple previous pregnancies, previous uterine surgery and previous D&C. It may be possible to diagnose placenta accreta with ultrasound.
If the initial episode of bleeding resolves, the mother and baby remain stable, and the fetus is premature, it is reasonable to delay delivery. The goal of this approach is to improve newborn outcome by allowing additional time for the baby to develop inside the uterus. Bed-rest usually is prescribed, steroids are given to hasten the development of the baby's lungs if needed. In women a negative blood type, an injection of Rh immune globulin or RhoGam is administered.
In patients who remain stable for a period of days after an initial episode of bleeding, the need for continued hospitalization is controversial. In selected patients, outpatient management in reasonable following the first episode of bleeding. If bleeding recurs, prolonged hospitalization may be necessary.
Cesarean section is the recommended method of delivery in nearly all cases of placenta previa. When possible, the procedure should be performed electively. Preparations should be made prior to delivery to ensure adequate venous access and ready availability of blood and necessary medications. If placenta accreta is anticipated, hysterectomy may be necessary and this should be discussed in advance. The management of placenta accreta encountered at cesarean section is discussed later in this chapter. Rarely, in the case of a low-lying or marginal placenta previa the descending fetal head may "tamponade" the bleeding placental edge and permit vaginal delivery. In the past, this possibility was assessed using a "double set-up" examination in which the patient was taken to the operating room and prepped for cesarean section. A careful examination then was undertaken to determine whether placental tissue could be seen or felt near the cervix, and the method of delivery was determined by the findings. Today, the "double set-up" examination largely has been replaced by ultrasound evaluation of placental location.
Placenta accreta is an abnormally firm attachment of placenta to the uterine wall Collectively termed "placenta accreta", three variants of the condition are recognized. In the most common form, accreta, the placenta is attached directly to the muscle of the uterine wall. This variant accounts for approximately 75-78%% of all cases. In approximately 17% of cases, the placenta extends into the uterine muscle and is termed placenta increta. In the remaining 5-7%, the placenta extends through the entire wall of the uterus and is termed placenta percreta.
The reported incidence of placenta accreta ranges from 1 in 540 to 1 in 70,000 deliveries, with an average incidence of approximately 1 in 7,000. The incidence of placenta accreta may be increasing because of the increasing number of women with previous cesarean sections.
In placenta accreta, the abnormally firm attachment of the placenta to the uterine wall prevents the placenta from separating normally after delivery. The retained placenta interferes with uterine contraction that is necessary to control bleeding after delivery. Severe bleeding and the surgical procedures performed in attempt to control it, are the major sources of maternal morbidity and mortality in cases of placenta accreta. Blood transfusions are required in more than 50% of patients with placenta accreta.
The principal newborn complication of placenta accreta is prematurity. Although earlier reports suggested increased perinatal mortality, recent studies do not confirm this association. Preterm birth complicates nearly two-thirds of cases, and the average gestational age at delivery is 34-35 weeks.
Several risk factors for placenta accreta have been identified. Among these, the most important appears to be placenta previa. Placenta accreta complicates approximately 10% of all cases of placenta previa. In the absence of placenta previa, accreta is rare. In patients with placenta previa the incidence of placenta accreta appears to
correlate with the number of previous cesarean sections. Maternal age greater than 35 and placental location overlying the previous uterine scar also increase the risk of accreta. Other reported risk factors include multiple previous pregnancies, previous uterine surgery, and previous D&C.
Placenta accreta should be suspected in all women with placenta previa. In the majority of cases, placenta accreta remains asymptomatic until delivery. Although bleeding prior to labor is not uncommon, it is more likely related to placenta previa than to placenta accreta. A definitive diagnosis of accreta is not possible prior to delivery. However, it may be possible to detect accreta with transvaginal ultrasound.
In women with placenta previa who are considered to be at high risk for placenta accreta, cesarean delivery should be performed electively whenever possible. The patient should be counseled preoperatively regarding the risks of hemorrhage, transfusion and hysterectomy. The operating room should be staffed by experienced personnel, and blood products should be readily available.
Unfortunately, most cases of placenta accreta are encountered without warning in women who are not prepared for the possibility of hysterectomy. Control of potentially life-threatening hemorrhage is the first priority, however the patient's desire for future fertility must be taken into consideration. Historically, control of bleeding has been achieved by hysterectomy. However, In ten recent reports, including 31 cases of placenta accreta managed without hysterectomy, there were no maternal deaths, and subsequent fertility did not appear to be impaired.
Initial approaches to conservative management of placenta accreta may include curettage and/or over-sewing of the placental bed and occluding the blood vessels that supply the pelvis. Reported success rates of these maneuvers vary widely.
Another approach is to use X-ray guidance to inject gelatin sponge particles or spring coils into the blood vessels supplying the uterus. As noted previously, this technique is not feasible in most emergency situations.
There are several case reports of placenta accreta in which all or part of the placenta was left inside the uterus and managed expectantly. This is possible only in patients who are stable. It should be considered only in those who strongly desire future fertility and who understand and accept the risks of delayed bleeding and infection.
Conservative options may provide alternatives to hysterectomy in carefully selected patients. In the majority of cases, however, hysterectomy remains the procedure of choice.
Approximately 15% of all deliveries in the United State occur in women with previous cesarean sections. In a patient with a previous cesarean section, labor may cause the uterine scar to separate. Severe scar separation, also termed uterine rupture, can result in complete extrusion of the fetus into the maternal abdomen. In other cases rupture is associated with fetal distress or severe hemorrhage from the rupture site. In women undertaking a trial of labor with a previous low-transverse cesarean section, the risk of uterine rupture is less than 1%.
When uterine rupture is diagnosed or strongly suspected, surgery is necessary. In earlier reports of uterine rupture, most were managed with hysterectomy. In contrast, most cases today are managed by controlling the bleeding surgically and repairing the defect. Because of the risk of rupture recurrence in a subsequent pregnancy, women with previously-repaired uterine ruptures are advised not to attempt labor in the future. Ideally, a repeat cesarean section should be performed prior to the onset of uterine contractions.
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