Placenta Previa

History of Present Illness

The patient is a G6P4014 female in her 20’s who is 16 weeks pregnant and presents to the emergency department (ED) by ambulance with a chief complaint of vaginal bleeding. She reports that approximately one hour prior to presentation she experienced brisk post-coital vaginal bleeding. This was associated with abdominal cramping. Prior to her current symptoms, she was in her usual state of health and denies vaginal discharge, fever, nausea, and vomiting. Obstetric history is remarkable for a previous cesarean section, and a single episode of first trimester vaginal bleeding during the current pregnancy. The patient has had regular prenatal care, and a routine first trimester ultrasound demonstrated an intrauterine pregnancy (IUP) with no other abnormalities.

Past Medical History:  Asthma

Past Surgical History:  Cesarean section

Vital Signs: T 37.1  P 92  BP 116/69  RR 12  SpO2 100% on room air

Physical Exam: The patient is in no acute distress. Cardiac exam reveals a regular rhythm with borderline tachycardia. No murmurs, rubs, or gallops are present. Pulmonary and neurologic examinations are unremarkable. Her abdomen is soft and non-tender with a gravid uterus consistent with dates. Patient is lying on a chuck pad that is 50% saturated with blood. The external genitalia is normal in appearance with no rashes or lesions. The cervical os is closed. There is a moderate amount of active bright red blood coming from the os. 


Hgb: 11.9  Plt: 283  PTT: 34.9  INR: 1.1  Type/Rh: O+  Urinalysis: Large blood, nitrite/leukocyte esterase negative

Transvaginal Ultrasound: Placenta is anterior. Complete previa is noted, with hypervascularity which appears to invade myometrium, suspicious for accreta. Hypoechoic region present, possible placental lake or subchorionic hemorrhage. 

Hospital Course

Given the active bleeding from the cervical os and the patient’s relative tachycardia, the obstetric (OB) team was consulted and a formal ultrasound was obtained. It demonstrated complete previa and possible placenta accreta. Given the patient’s hemodynamic stability and absence of anemia in the ED, blood products were withheld. She was RH positive, so RhoGAM was also not administered. The patient was admitted to the OB service. During admission, a pelvic MRI was obtained and verified complete previa with accreta. She had no further episodes of bleeding as an inpatient and was discharged on hospital day two. Her hemoglobin nadir was 10.1 during that admission. 

Four days after discharge, the patient had a second episode of bleeding with an estimated blood loss of 200 mL. She was again admitted to the OB service for observation and was eventually discharged after two weeks without significant bleeding during her hospitalization. She was then readmitted two days later after an additional bleeding episode. She remained hospitalized for the remainder of her pregnancy and experienced several episodes of minor bleeding during her final admission. At 24 weeks, she received magnesium for tocolysis and betamethasone for fetal maturation following an episode of moderate bleeding. 

At 29 weeks, the patient had a significant episode of bleeding with an estimated blood loss of 500 mL. An emergent cesarean hysterectomy was performed. She required two units of red blood cells intra-operatively and had a brief intensive care unit (ICU) stay following the surgery for hemodynamic monitoring. She did well post-operatively and was discharged on post-operative day five. Her infant was admitted to the neonatal ICU upon delivery and required intubation for hypoxemia. His hospital course has been complicated by hyperbilirubinemia requiring phototherapy, with a protracted ICU course.


Normal placental implantation is in the upper segment of the uterus. Placenta previa is defined as a placenta that is in close proximity to, or overlies the internal os of the cervix. It is present to some degree in 1 in 200 pregnancies.[1] Historically, there are four categories of previa each defined by proximity of the placenta to the cervical os. These range from a low-lying placenta, which extends into the lower uterine segment but does not reach the os, to a complete previa where the placenta completely covers the os.[2]

Figure 1.  Abnormal placental implantation. Art courtesy of nicole soria, MD.

Placenta accreta occurs in approximately 10% of women with previa and is relatively rare outside of the context of previa.[3] Accreta is defined as an abnormal attachment of the placental villi to the uterine wall. It occurs in approximately 1 in 500 pregnancies.[1] In its least invasive form it is simply referred to as placenta accreta. In this iteration, the placenta attaches directly to the myometrium through a defect in the decidua basalis. In placenta increta, the placenta invades the myometrium. In placenta percreta, the placenta invades through the myometrium and may attach to intraperitoneal structures such as bowel or bladder. Confusingly, the term placenta accreta may also be used to encompass the entire spectrum of these conditions (for example, a placenta accreta may refer to a true accreta, an increta, or a percreta).[3] 

Risk factors for placenta previa include prior cesarean delivery (with increasing risk with greater number of cesareans), advanced maternal age, recurrent abortions, multiparity, and infertility treatment.[4]  Risk factors for placenta accreta are similar to those of previa and include smoking, hypertensive disorders, low socioeconomic status, short caesarean to conception interval, and female fetus.[5] There are significant adverse outcomes associated with previa that can occur to both the mother and the child. Poor maternal outcomes include increased rates of peripartum hysterectomy, second trimester bleeding, maternal blood transfusion, maternal sepsis, vasa previa, malpresentation, and postpartum hemorrhage.[4] Poor neonatal outcomes include increased mortality, lower birth weight, Apgar score less than seven after one and five minutes, congenital malformations, and intrauterine growth retardation.[4] Notably, rates of placenta previa and accreta have been increasing since the 1950’s. This is largely attributable to the increase in cesarean section over this time period.[1] 

Placenta previa generally presents as painless vaginal bleeding occurring in the second or third trimester. It is essential that this diagnosis be excluded in all women presenting with vaginal bleeding after the first trimester because it has implications for the remainder of the pregnancy. Emergency department (ED) evaluation should include a thorough history including quantifying bleeding. Occasional vaginal spotting is often less concerning than heavy flow, such as in the presented case. Placenta previa classically presents without abdominal pain, helping to distinguish it from spontaneous miscarriage and other causes of vaginal bleeding in pregnancy. 

Physical exam should focus on identifying signs of hemodynamic instability and significant anemia. Some obstetricians recommend delaying both digital and speculum exam until placental location can be verified. This is not well supported in the literature, and some obstetricians recommend performing speculum examination to exclude other sources of vaginal bleeding such as infection, malignancy, or laceration prior to undertaking transvaginal ultrasonography. In this case, great care should be taken not to directly manipulate the cervix.

Diagnosis of placenta previa is typically via transvaginal ultrasound, which is highly sensitive and specific for the diagnosis.[4] Transabdominal ultrasound lacks sufficient sensitivity, as evident in the above patient who had a normal transabdominal ultrasound earlier in her pregnancy. Translabial ultrasound shows similar test characteristics to transvaginal ultrasound and may also be considered, though transvaginal ultrasound is usually well tolerated with little bleeding risk when performed appropriately. 

Once identified in the ED, consultation with an obstetrician is warranted as these patients often require admission for monitoring at the very least. These patients are at risk of severe vaginal bleeding. Therefore, emergency providers should prioritize stabilization of the patient including administration of fluids and blood products if necessary. Prevention of Rh isoimmunization is also indicated. It is recommended to avoid allowing these patients to eat or drink because they are at high risk of decompensation and may require early fetal delivery if symptoms do not improve. Ultimately, disposition of patients with placenta previa or accreta should be made in conjunction with the obstetrics team.  

Approximately 20% of previas will resolve prior to delivery, through so called placental “migration.” Consequently, women diagnosed with previa early in pregnancy should have repeat ultrasonography performed later in pregnancy to re-evaluate the location of the placenta. Placental migration is thought to occur due to differential growth whereby the placenta grows towards the fundus, which contains a more robust blood supply. The less vascularized portions of the placenta close to the cervix will then atrophy. While this is generally considered a favorable outcome, the risk of vasa previa is increased. In this condition, fetal vessels course within the placental membranes but are unsupported by the placenta and are dangerously close to the cervical os. These vessels are at high risk for tearing at the time of membrane rupture, with a subsequent risk of fetal exsanguination.[6] 

As placenta accreta usually presents in conjunction with placenta previa, the diagnosis is most often made by ultrasonography, either as part of routine antenatal testing or due to vaginal bleeding in the second or third trimester. Unfortunately, the false negative rate for the diagnosis of accreta by transvaginal ultrasound approaches 20%, and this diagnosis is often made when catastrophic hemorrhage results from attempts to deliver the placenta at birth.[7] Pelvic MRI is another diagnostic modality that may be considered. Test characteristics are fairly similar to transvaginal ultrasound, however. Nonetheless, its sensitivity is somewhat improved for posterior placenta accretas.[8]  

Previa is managed conservatively in the antenatal period. This may be done in the outpatient setting in the absence of bleeding. However, many women will have recurrent bleeding requiring multiple hospitalizations for monitoring and blood product administration. Patients with previa should be delivered by scheduled caesarean if at all possible. Some women with low lying placentas less than 2 cm from the cervical os may be appropriate for a trial of labor, but the risk of hemorrhage is high and a double setup should be considered. Optimal timing of delivery is also controversial but is generally recommended to occur at 36 weeks' gestation as this optimally balances fetal maturity with risk of bleeding. Women who develop significant but non life-threatening vaginal bleeding may benefit from tocolytic administration. Steroid administration is also routinely performed to promote fetal lung maturity prior to delivery.[6] 

There are few beneficial interventions that may be initiated prior to delivery in the case of placenta accreta. Unfortunately, accreta is associated with significant morbidity due to the highly vascular nature of the placenta and associated bleeding risk. Most women with accreta are managed with caesarean hysterectomy in which the woman undergoes a caesarean section with hysterectomy at the time of delivery. Attempts to preserve fertility by delivery of the placenta and omission of hysterectomy have been attempted and are associated with high bleeding risk. There have been small studies reporting successful fertility preservation by making no attempt to deliver placenta at the time of delivery and instead administering methotrexate and monitoring for placental expulsion.[10] 

A recent small prospective study also demonstrated that fertility may be preserved by abortion followed by methotrexate administration and dilation and curettage for retained products of conceptus. On average, even with caesarean hysterectomy, the average blood loss is on the order of several liters and ICU admission is common. Additional complications include maternal sepsis, injury to bowel and bladder, and fstula formation.[11] In cases where accreta is diagnosed antenatally, caesarean is scheduled when fetal lung maturity is achieved (typically at 36 weeks). In cases where accreta is not diagnosed antenatally or emergent surgery is necessitated due to hemorrhage, morbidity and mortality are increased.[10] 

Placenta previa is a potentially life-threatening diagnosis often complicated by accreta. While definitive management requires advanced obstetric care, appropriate ED care is essential. These conditions should be considered in all cases of second and third trimester vaginal bleeding even when transabdominal ultrasonography has previously demonstrated no abnormality. A careful speculum examination is warranted, but care should be taken to avoid manipulation of the cervix. Digital examination is contraindicated. Basic supportive care should be initiated including volume resuscitation as needed. Obstetrics should be involved early in evaluation particularly if bleeding is brisk or there is evidence of hemodynamic instability.

Authored by david habib, md

posted by matthew Scanlon, MD


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  8. Everett, M., Cummings, J., Neiderhauser, A., Rodriguez-Thompson, D., et al. Antepartum bleeding of unknown origin in the second half of pregnancy: a review. Obstetrical and Gynecological Survey, 2005(11): 741-745. 
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  11. Fitzpatrick, K., Sellers, S., Spark, P., Kurinczuk, J., et al. The management and outcomes of placenta accreta, increta, and percreta in the UK: a population-based descriptive study. BJOG, 2014(1): 62-70. 
  12. Lin, K., Qin, J., Xu, K., Hu, W., et al. Methotrexate management for placenta accrete: a prospective study. Archives of Gynecology and Obstetrics, 2015(6): 1259-1264.