Thrombosis in Pregnancy
Ileofemoral vein thrombosis accounts for approximately 90% of proximal thromboses in pregnancy, occurring most often in the left lower extremity.20 The incidence of isolated iliac vein thrombosis in pregnancy is low, but when it does occur, delay in diagnosis can lead to significant morbidity. Therefore, for women with suspected isolated iliac vein thrombosis in whom CUS is negative or nondiagnostic, magnetic resonance direct thrombus imaging (MRDTI) should be performed.21 Patients with iliac vein thrombosis may present with unexplained inguinal, pelvic, or abdominal pain, which may be accompanied by back pain, and they usually present with swelling of the entire leg. MRDTI does not require gadolinium contrast and its accuracy appears to be similar to that of venography for iliac vein thrombi in the nonpregnant population.21 Exposure to gadolinium during pregnancy is associated with an increased risk for rheumatologic, inflammatory, or infiltrative skin conditions and stillbirth or neonatal death.22
Ovarian vein thrombosis is a rare but serious diagnosis. It occurs mostly in the postpartum period, mainly after cesarean delivery, and usually affects the right ovarian vein. The diagnosis is confirmed by ultrasound, computed tomography (CT), or magnetic resonance imaging.23
PULMONARY EMBOLISM
PE is more difficult to diagnose than DVT, particularly because clinical signs of PE are unreliable in the pregnant patient. The mortality rate of untreated PE is high, ranging from 18% to 38%, and approximately one-third of patients with untreated thromboembolic disease develop recurrent embolism.24 Studies have reported a PE prevalence between 1.4% and 4.2% in pregnant women with suspected clinical diagnosis of PE.25
,The clinical presentation of PE and associated laboratory testing results may be subtler in pregnant than in nonpregnant patients. Arterial blood gases (ABG) may show hypoxemia or hypocapnia. The ABG in pregnancy has a sensitivity of 76.9%, specificity of 20.2%, and negative and positive predictive values of 80% and 11.5% for PE, respectively.26 The alveolar-arterial oxygen gradient is a poor screening test for PE during pregnancy and postpartum. A retrospective chart review of 17 pregnant women with documented PE showed that 58% had normal alveolar-arterial gradients.27 Therefore, in a pregnant woman with a history suspicious for PE, objective imaging studies should be performed even if the patient has normal ABG.
The 2011 guidelines from the American Thoracic Society (ATS) and the Society of Thoracic Radiology (STR) recommend against using D-dimer to diagnose PE in pregnancy.28 In addition, lower extremity CUS should only be performed as the first diagnostic imaging procedure if the patient has signs or symptoms of DVT. Instead, the ATS/STR guidelines recommend a plain radiograph of the chest as the first imaging test. If the chest radiograph is normal, a ventilation/perfusion scan (V/Q) scan is preferred over CT pulmonary angiography (CTPA). Diagnostic accuracy of the V/Q scan may be superior to CTPA in pregnancy, and it is preferable because of the lower prevalence of indeterminate V/Q scan in pregnant women.29 Moreover, there is lower radiation exposure to the maternal breast and lung tissue with a V/Q scan than with CTPA. CTPA confers lower fetal radiation doses than V/Q scans (0.03–0.66 mGy versus 0.32–0.74 mGy, respectively) but higher total body maternal radiation (4–16 mSv versus 1–2.5 mSv).30 A quantitative approach to lung scan interpretation, based on the distribution histogram of V/Q ratios, may be helpful in categorizing patients with suspected PE.28 A study of 121 suspected episodes of PE in 120 pregnant women showed that 104 women with normal or nondiagnostic scans did not develop subsequent episodes of VTE during a mean follow-up period of 20 months.31
If the baseline chest radiograph is abnormal in a pregnant woman with clinical suspicion of PE, a CTPA should be performed. As noted, fetal radiation doses for CTPA examinations in which the fetus is not directly imaged are minimal. If CTPA is recommended for the diagnosis of PE, the patient should be informed that radiation to the breast may increase her baseline risk for breast cancer. The ATS guidelines state that “given the lack of evidence documenting clear superiority of any one diagnostic test, the values and preferences of a patient and her physician likely will and should determine the final choice and sequence of tests performed.”28
CASE I CONTINUED
Upon presentation to the emergency department, the circumference of the patient’s left leg is not significantly greater than that of her right leg, and her leg pain has resolved. Bilateral CUS is negative for proximal or distal DVT. Chest radiograph shows an opacification of her left lower lobe. CTPA shows bilateral segmental and subsegmental lower lobe pulmonary emboli.
How does risk for VTE change throughout pregnancy?
Women are at increased risk for VTE throughout the entire pregnancy, starting from conception, but mainly during the postpartum period. A Danish historical controlled cohort study of 819,751 pregnant women (ages 15–49 years) over a 10-year period identified 727 women with VTE. The absolute risk for VTE per 10,000 pregnancy-years increased from 4.1 (95% CI 3.2 to 5.2) during weeks 1 to 11 to 59.0 (95% CI 46.1 to 76.4) in week 40 and decreased in the postpartum period from 60 (95% CI 47.2 to 76.4) during the first week after birth to 2.1 during weeks 9–12 after birth (95% CI 1.1 to 4.2).32 This study showed that the risk of VTE increases throughout pregnancy and reaches its maximum during the peripartum period and is not significantly increased after 6 weeks post-delivery. In a retrospective cross-over cohort study of 1,687,930 women in California who delivered their first newborn, an elevated risk of VTE persisted until at least 12 weeks after delivery. However, the absolute increase in risk after 6 weeks postpartum was low.33
CASE 1 CONCLUSION
The patient is started on anticoagulation therapy and carefully monitored during the remainder of the pregnancy and postpartum period. Anticoagulation is discontinued 6 weeks after delivery.
