The role of ultrasound in life-threatening situations in pregnancy.

Pregnant women are at an increased risk of a number of conditions that are associated with bleeding. Conditions such as ectopic pregnancy, retained products of conception, placenta previa, abruptio placentae, morbid adhesion of the placenta, and postpartum hemorrhage can be associated with massive bleeding that endangers the maternal life and health. Screening, early detection, and prevention play a key role in reducing maternal morbidity and mortality caused by these conditions. Ultrasound, in experienced hands, is an effective tool that can assist in diagnosing many of these obstetrical conditions. The advances in technology and the non-invasive nature of ultrasound examination have made it popular in our daily obstetrical practice. The review discusses the role of ultrasound in the most common life-threatening conditions during pregnancy.

INTRODUCTION

Vaginal bleeding associated with pelvic or abdominal pain are the most common complaints of pregnant women presenting to the emergency department. In addition to clinical history, physical examination, and laboratory data, ultrasound examination is essential for evaluating these patients. Over the last five decades, technology has provided ultrasound machines of high quality and resolution with the option of compact and mobile units. This has made it a useful tool for obstetrical assessment and diagnosis in emergencies.

Ultrasound has become an important tool in routine obstetrical care. This review limits itself to the role of ultrasound in some of the most common emergency conditions during pregnancy and the immediate postpartum period.

Ectopic pregnancy

Although maternal mortality rate attributed to ectopic pregnancy has dropped by about 50% in the past two decades in the developed country, it remains to be a common cause of morbidity and mortality in other parts of the world.[1] The major causes of death are excessive hemorrhage, shock, and renal failure. Therefore, ectopic pregnancy must be excluded in every woman in childbearing age. Physicians should be aware of the risk factors for ectopic pregnancy such as history of ectopic pregnancy, intrauterine contraceptive device, and pelvic inflammatory disease.

Pelvic pain is the most common symptom of an ectopic pregnancy. The classic triad of vaginal bleeding, adnexal tenderness, and an adnexal mass is present in less than 30% of ectopic pregnancies. The presence of a normal menstrual period should not exclude the possibility of an ectopic pregnancy.

Sonographic findings

A normal intrauterine gestational sac is eccentrically placed in the endometrial cavity and surrounded by a double decidual layer. This should not be confused with the pseudo sac that is formed due to the hormonal changes associated with an ectopic pregnancy and results in an endometrial fluid collection surrounded by a single decidual layer. The presence of a yolk sac confirms an intrauterine pregnancy [Figure 1].

Figure 1

An intrauterine gestational sac with a double ring sign. A yolk sac is seen within the gestational sac. The star marks the inner ring and the two triangles mark the outer ring. YS-yolk sac

A complex adnexal mass of mixed echogenicity may be imaged following the rupture of an ectopic pregnancy. Occasionally, hemoperitoneum may be completely anechoic [Figure 2]. This should not be confused with the small amount of peritoneal fluid that may be present in normal pregnancy due to exudation from normal corpus luteum. Color doppler might be of help in the demonstration of the increased vascularity (ring of fire) around the ectopic pregnancy. In the absence of a detectable intrauterine gestation sac, transvaginal ultrasound should be used in conjunction with quantitative human chorionic gonadotropin (HCG) to increase the detection rate of unruptured ectopic pregnancy.[2]

Figure 2

Free fluid collection posterior to the uterus. The star marks the uterus and the triangle marks the free fluid collection

Retained products of conception/incomplete miscarriage

Retained products of conception might result in severe vaginal hemorrhage or provide a nidus for uterine infection. Sonographic findings include endometrial thickening showing heterogeneous echogenic material and focal areas of hyperechogenicity that may represent retained products of conception.[3]

Placenta previa

Placenta previa is defined as implantation of the placenta in the lower uterine segment. A placenta that is inserted at a distance less than 2 cm from the internal cervical os is defined as a low-lying placenta.[4] The term “major placenta previa” indicates that the placenta is covering the internal cervical os [Figure 3]. The incidence of placenta previa is 0.5% at term. The neonatal mortality associated with placenta previa is four times that of other pregnancies.[5] Up to 15% of massive postpartum hemorrhage and maternal near-miss cases are caused by placenta previa and abruptio placentae.[6]

Figure 3

A posterior implanted placenta reaching and covering the internal cervical os. The arrow marks the placenta, the star marks the maternal bladder, and the triangle marks the cervix

Multiparity, prior cesarean section and uterine curettage are the major predisposing factors for placenta previa . Because of the risk of provoking life-threatening hemorrhage, a digital vaginal examination is contraindicated until placenta previa is excluded. Transabdominal ultrasound might be a suitable approach when the placenta is inserted in the anterior wall. A mildly filled maternal bladder will help identify the lower uterine segment. However, transvaginal ultrasound is ideal when the placenta is inserted in the posterior uterine wall.[7]

Morbid adhesion of the placenta (accreta/increta/percreta)

Placenta accreta is defined as penetration of the chorionic villi into the superficial layer of the myometrium. The term increta is used when the chorionic villi penetrate the myometrium, while placenta percreta indicates that the placenta has penetrated through the uterine wall reaching peritoneal layer. The incidence of placenta accreta has increased steadily over the last few years from approximately 1/30,000 deliveries to 1/533 deliveries. This is attributed mainly to the increased rate of Cesarean sections. If encountered unexpectedly, morbid adhesion can lead to catastrophic blood loss. The antenatal diagnosis can help in reducing maternal morbidity and mortality, as the place and time of delivery as well as appropriate surgical approach can be planned in advance.[8]

The main sonographic features for morbid adhesion of the placenta are thinning from the retroplacental hypoechoic zone, presence of multiple placental lakes (“Swiss cheese” appearance), thinning of the uterine serosa–bladder wall complex, elevation of tissue beyond the uterine serosa, turbulent or complicated blood flow at the uteroplacental interface, and irregular blood flow underlying the maternal urinary bladder [Figure 4]. The last four features raise the suspicion of placenta percreta. Morbid adhesion of the placenta should be excluded in patients with anterior implanted placenta and history of repeated Cesarean section.[9]

Figure 4

A morbid adherent placenta. This is indicated by the increase blood flow

Placental abruption

Placental abruption, or abruptio placentae, is defined as premature separation of a placenta implanted in the upper segment. External vaginal bleeding does not always occur; approximately 40% of cases have concealed retroplacental hemorrhage. The incidence of placental abruption is 1/100 births.[10] Pre-eclampsia, hypertension, maternal vascular disease, smoking, prior placental abruption, external trauma, etc are some of the major risk factors. The perinatal mortality rate associated with abruptio placentae is reported to be as high as 53%, and the near-miss maternal morbidity is as high as 22%. This is mainly due to the associated hypovolemic shock and coagulation failure.[11]

The sensitivity of an ultrasound examination in detecting placental abruption is as low as 25%. Therefore, physicians should rely on the clinical presentation for diagnosis. The main clinical features are vaginal bleeding associated with abdominal pain, tachycardia, drop in blood pressure, hard abdomen on palpation, and signs of fetal distress. Requesting an ultrasound examination in such patients is of little significance and might waste valuable time.

CONCLUSIONS

Pregnancy might become complicated due to several conditions that are life threatening such as ectopic pregnancy, placenta previa, abruptio placentae, and morbid adhesion of the placenta. Ultrasound is an important and helpful tool in the investigation and diagnosis of such conditions. However, healthcare providers should be aware of its limitations. Therefore, as an adjunct diagnostic tool, it should not override their clinical judgment.