May-Thurner Syndrome in Pregnancy: a Multi-Institutional Case Series and Review of the Literature.

May-Thurner syndrome (MTS), also known as iliac vein compression syndrome, is one of the least recognized causes of deep venous thrombosis (DVT) in reproductive-aged women. First reported by May and Thurner1May R. Thurner J. The cause of the predominantly sinistral occurrence of thrombosis of the pelvic veins.Angiology. 1957; 8: 419-427Crossref PubMed Scopus (471) Google Scholar in 1957, this anatomic variant involves compression of the thin-walled left common iliac vein by the thick-walled overriding right common iliac artery, resulting in intraluminal collagen deposition, sluggish venous flow, and increased risk of proximal DVTs. The prevalence of MTS ranges from 18% to 49% among patients diagnosed as having iliofemoral vein thrombosis, but MTS can also be diagnosed incidentally during imaging for other indications.2Kasirajan K. Gray B. Ouriel K. Percutaneous Angio-Jet thrombectomy in the management of extensive deep venous thrombosis.J Vasc Interv Radiol. 2001; 12: 179-185Abstract Full Text Full Text PDF PubMed Scopus (190) Google Scholar In the physiological gravid state, the risk of venous thromboembolic (VTE) disease increases considerably secondary to venous stasis from mechanical compression of vessels by the gravid uterus and changes in the coagulation profile owing to hormonal alterations.3Danilenko-Dixon D.R. Heit J.A. Silverstein M.D. et al.Risk factors for deep vein thrombosis and pulmonary embolism during pregnancy or postpartum: a population-based, case-control study.Am J Obstet Gynecol. 2001; 184: 104-110Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar The incidence of VTE in pregnancy or postpartum period is 4 to 5 times higher than in nonpregnant women of the same age.4James A.H. Jamison M.G. Brancazio L.R. Myers E.R. Venous thromboembolism during pregnancy and the postpartum period: incidence, risk factors, and mortality.Am J Obstet Gynecol. 2006; 194: 1311-1315Abstract Full Text Full Text PDF PubMed Scopus (616) Google Scholar Although a handful of case reports have been published on MTS in pregnancy in recent years, there is an overall dearth of literature on this condition and therapeutic options and outcomes. We present a large case series of management and outcomes for MTS in pregnancy. We performed a retrospective chart review of 25 patients with MTS who experienced 1 or more pregnancies over a 6-year period (2013–2019) at 1 of 2 urban maternal-fetal medicine referral centers. Both medical centers are tertiary referral centers with ethnically diverse patient populations. The following patients were excluded: <18 years of age, fetal demise, or lethal fetal anomalies. This study was approved by the institutional review boards (IRBs) of the University of California, Los Angeles (IRB #18-002070), and Yale School of Medicine (IRB #2000024850). Electronic medical records were reviewed for maternal demographics, management protocols, and obstetrical outcomes. Maternal demographics included age, parity, race and ethnicity, prenatal care and delivery provider, and MTS characteristics. Management protocols included anticoagulation and presence of iliac stent. Obstetrical and perinatal variables included postpartum hemorrhage (defined as blood loss of >1000 mL for either vaginal or cesarean delivery) and maternal intensive care unit (ICU) admission. A total of 30 pregnancies were identified in 25 patients with MTS, 6 from site 1 and 19 from site 2. Of note, 24 of the pregnancies carried a diagnosis of MTS during the antepartum course (diagnosed before or during pregnancy), with 6 diagnosed after delivery. Demographics are listed in the Table and include maternal characteristics related to MTS diagnosis, presence of VTE, mode of diagnostic imaging, presenting symptoms, and concurrent thrombophilia mutations. Of the 24 pregnancies in which patients had an antenatal diagnosis of MTS, antepartum anticoagulation was prescribed in 23 cases (95.8%). Specific anticoagulation regimens are detailed in the Figure. Therapeutic dosing consisted of enoxaparin 1 mg/kg titrated to an anti-Xa level of 0.6 to 1.0, intermediate dosing consisted of enoxaparin 40 mg twice daily, and prophylactic dosing consisted of enoxaparin 40 mg daily. Notably, 1 patient with antepartum MTS diagnosis in the absence of DVT history declined anticoagulation. Of the 30 pregnancies, 26 (86.7%) resulted in term deliveries, 2 iatrogenic preterm, and 2 spontaneous preterm deliveries; 13 (43.3%) were through cesarean delivery. Neuraxial analgesia was used in 28 deliveries (93.3%), including all cases of cesarean delivery. Furthermore, 2 patients (6.7%), both multiparous, underwent unmedicated precipitous vaginal deliveries. There were 2 cases of postpartum hemorrhage, both postcesarean with multifetal gestations on therapeutic anticoagulation. There was 1 maternal ICU admission for administration of a heparin drip in anticipation of a thrombolysis procedure. Median birthweight was 3100 g (interquartile range, 2792–3347.5). Furthermore, 4 neonates (13.3%) required neonatal ICU admissions, but there were no cases of neonatal intraventricular hemorrhage, birth trauma, seizure, or respiratory distress syndrome.TableDemographics and baseline characteristicsCharacteristicTotal pregnancies (n=30)Total patients (n=25)Number of fetuses Singletons27 (90)N/A Twins2 (6.7)N/A Triplets1 (3.3)N/A Maternal age, yN/A34.0 (30.5–37.5)Race and ethnicity WhiteN/A21 (84) BlackN/A1 (4) HispanicN/A0 (0) AsianN/A0 (0) Mixed raceN/A1 (4) UnspecifiedN/A2 (8)Maternal characteristics BMI, prepregnancy, kg/m226.3 (22.7–29.8)N/A Gestational weight gain, lb23.0 (15.0–30.0)N/A Spontaneous conception24 (80)N/A In vitro fertilization6 (20)N/AObstetrical care Generalist prenatal provider6 (20)N/A MFM prenatal provider11 (36.7)N/A Comanagement by both13 (43.3)N/A Generalist delivery provider17 (56.7)N/A MFM delivery provider13 (43.3)N/AVenous thromboembolic events Total deep venous thrombosis20 (66.7)N/A DVT diagnosed before pregnancy9/20 (45)N/A DVT diagnosed during pregnancy10/20 (50)N/A DVT diagnosed postpartum1/20 (5)N/A Total pulmonary embolism6 (20)N/A PE diagnosed before pregnancy5/6 (83.3)N/A PE diagnosed during pregnancy1/6 (16.7)N/ATiming of MTS diagnosis PreconceptionN/A14 (56) AntepartumN/A6 (24) PostpartumN/A5 (20) Concomitant inheritable thrombophilia mutationN/A11 (44)Diagnostic modality Duplex ultrasound onlyN/A6 (24) MRI onlyN/A7 (28) Duplex ultrasound plus MRIN/A3 (12) VenogramN/A6 (24) Unreported imagingN/A3 (12)Most common presenting symptomsaA total of 3 patients with prepregnancy diagnosis of MTS did not have records available for review owing to remote diagnosis of MTS. PainN/A17/22 (77.3) SwellingN/A17/22 (77.3) ErythemaN/A6/22 (27.3) VaricositiesN/A4/22 (18.2) Pelvic congestionN/A2/22 (9.1) Iliac stents placed preconceptionN/A8/10 (80) Iliac stents placed postpartumN/A2/10 (20)Data are presented as number (percentage) or median (IQR).BMI, body mass index; DVT, deep venous thrombosis; IQR, interquartile range; MFM, maternal-fetal medicine; MRI, magnetic resonance imaging; MTS, May-Thurner syndrome; N/A; not applicable; PE, pulmonary embolism.Mei. May-Thurner syndrome in pregnancy: a case series and review of literature. AJOG MFM 2020.a A total of 3 patients with prepregnancy diagnosis of MTS did not have records available for review owing to remote diagnosis of MTS. Open table in a new tab Data are presented as number (percentage) or median (IQR). BMI, body mass index; DVT, deep venous thrombosis; IQR, interquartile range; MFM, maternal-fetal medicine; MRI, magnetic resonance imaging; MTS, May-Thurner syndrome; N/A; not applicable; PE, pulmonary embolism. Mei. May-Thurner syndrome in pregnancy: a case series and review of literature. AJOG MFM 2020. Current national guidelines recommend treating pregnant patients with active thrombosis using therapeutic anticoagulation and treating those with remote history of thrombosis or stents using prophylactic anticoagulation.5American College of Obstetricians and Gynecologists’ Committee on Practice Bulletins—ObstetricsACOG Practice Bulletin No. 196: thromboembolism in pregnancy.Obstet Gynecol. 2018; 132: e1-e17Crossref PubMed Scopus (70) Google Scholar In this case series, the anticoagulation regimens used for the pregnant patients with MTS deviate slightly from the standard guidelines, with MTS prompting prophylactic anticoagulation without previous VTE and some providers opting for intermediate or therapeutic dosing with previous pulmonary embolism. Obstetrical outcomes were largely favorable in our large series. Most pregnancies resulted in term deliveries with appropriately grown fetuses, including patients with concomitant inheritable thrombophilias. Although the cesarean delivery rate was slightly higher than national average, all women undergoing cesarean delivery were able to receive neuraxial analgesia. The limitations of our study include its geographic restriction to 2 large urban areas with patient populations who could readily access a tertiary level referral center with subspecialty care. More research is needed in evaluating outcomes of patients with less access to subspecialists and whether standardized protocols for the management of MTS in pregnancy could prevent the need for transfer of care. Our study was also limited by the lack of records regarding the details of initial MTS diagnosis, including the percentage of narrowing in the iliac veins. Despite these limitations, our case series is one of the largest to date of pregnant patients with MTS and indicates that appropriate management and awareness of the risks of VTE in pregnancies affected by MTS can yield favorable maternal and neonatal outcomes. MTS should be considered as part of the differential diagnosis in female patients with iliofemoral DVT, especially when pregnant. The patient with incidental MTS diagnosed by intraluminal narrowing and sluggish flow in the left common iliac vein, even in the absence of DVT history, should be considered at risk. Future work is needed in randomized clinical trials comparing the various treatment modalities in pregnant patients in the hopes of creating specific guidelines for the management of women with MTS during pregnancy.