Hemorrhagic shock is the most common form of shock encountered in obstetric practice. Interventions that may limit transfusion requirements include normovolemic hemodilution, use of recombinant activated factor VII, selective embolization of pelvic vessels by interventional radiology, and the use of the cell saver intraoperatively. Current understanding of the mechanisms of acute coagulopathy calls into question the current transfusion guidelines, leading to a tendency to apply massive transfusion protocols based on hemostatic resuscitation despite lack of prospective data.
A 27-year-old patient with a history of 3 previous cesarean sections presents for her fetal anatomy scan at 22 weeks. On ultrasound (US) examination, an anterior placenta previa is noted with multiple lacunae and attenuation of the retroplacental space.
Hemorrhagic shock is the most common form of shock encountered in obstetric practice. In 2005, in the United States, hemorrhage was the third leading cause of maternal death because of obstetric factors.
Historically, the most frequent indication for a peripartum hysterectomy has been uterine atony. Recent literature suggests that this indication may be shifting, with abnormal placentation becoming the most common reason for peripartum hysterectomy. The incidence of placenta accreta is estimated at 1 in 533 pregnancies. With the increasing cesarean section rate as well as a decrease in vaginal birth after cesarean section, this number is likely to increase in the future.
In this article, we will address some of the new concepts in the medical management of obstetric hemorrhage. We will focus on a theoretical case of placenta accreta; however, many of the therapeutic recommendations apply to any cause of massive obstetric bleeding.
Antepartum care
In the vast majority of cases, placenta accreta may be presumptively diagnosed on the basis of US alone. Sonographic findings suggestive of accreta include the presence of placental lacunae giving a “Swiss cheese” appearance, loss of the normal retroplacental hypoechoic space, and increased vascularity with uterine wall vessel invasion as noted by the use of color Doppler.
In recent years, there has been increased interest in the use of magnetic resonance imaging (MRI) for the evaluation of patients with suspected placenta accreta because it can provide information on depth of invasion and may be particularly useful in the diagnosis of posteriorly located placentas. MRI findings suggestive of placenta accreta include lower uterine bulging, heterogeneous placenta, and dark intraplacental linear bands on T2-weighted images.
In a multicenter retrospective study, Dwyer et al compared the accuracy of both US and MRI in the diagnosis of placental accretism. The sensitivities for the diagnosis of placenta accreta with US and MRI were 93% and 80%, respectively. Specificities (negative study in the absence of the condition) were 71% and 65%, respectively. Neither difference achieved statistical significance. The accuracy for the diagnosis may be increased by complementing the abdominal US with transvaginal sonography.
The use of paramagnetic contrast media in MRI (gadolinium) likely would improve the diagnostic performance of MRI; however, the agent crosses the placenta, and the effects on the fetus are unknown.
At present, it appears that the diagnostic abilities of both US and MRI are similar. In cases where the diagnosis is unclear, MRI and US may be used as complementary tests.
In patients with suspected placenta percreta, we recommend a complementary MRI to better define the extent of invasion to adjacent organs (eg, bladder, bowel) so that appropriate preoperative planning may be undertaken (eg, placement of ureteral stents).
Once the diagnosis is suspected, patients should receive iron and/or folic acid as needed to maintain normal hemoglobin values. Occasionally, patients may require recombinant erythropoietin as adjuvant therapy. Patients should ideally be referred to a center with a multidisciplinary team available, including maternal fetal medicine, general surgery, urology, vascular surgery, interventional radiology, blood bank, and neonatology. Maternal morbidity is reduced in women with placental accretism who deliver in tertiary care centers.
Recent evidence questions the need for serial fetal growth USs in the setting of placenta previa without accretism, as it does not increase the risk of intrauterine growth restriction. In the setting of suspected accretism, however, we recommend sonographic follow-up every 3-4 weeks to evaluate placental location, depth of invasion, and fetal growth.
Occasionally, patients at risk for severe hemorrhage may benefit from preoperative autologous blood donation. Patients donate units of their own blood during pregnancy, and such products will be stored in the blood bank for use on the day of surgery. Theoretically, the hemoglobin will recover (patients will be on iron supplements) between donations. In practice, however, anemia is a limiting factor, and patients usually donate only a limited number of units throughout pregnancy. This technique will not prevent the risks associated with blood collection, storage, and administration and may not be acceptable to Jehovah’s Witnesses. Overall, the technique is not cost effective and is recommended only for patients with rare blood types and/or alloimmunization to rare antibodies for whom immediate availability of allogeneic blood products may be limited.
Timing of delivery in women with placental accretism is a controversial subject. A recent decision analysis model suggested that delivery at 34 weeks of gestation may be optimal and that amniocentesis for determination of fetal lung maturity does not improve outcomes and is not recommended. Advanced planning and interdisciplinary collaboration are fundamental, and as gestational age increases, so does the risk of emergent bleeding. We concur with these recommendations: patients with suspected accretism should be delivered between 34 and 37 weeks. Recent evidence suggests that patients with placenta previa and a cervical length less than 30 mm have a higher risk of acute hemorrhage. In deciding whether to deliver patients closer to 34 weeks vs 37 weeks, clinicians may consider obtaining a cervical length by transvaginal US. If the cervix is less than 30 mm and the gestational age more than 34 weeks, we favor delivery as opposed to waiting a “few” more weeks (no later than 37 weeks) to prevent bleeding and emergent deliveries.
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