Magnetic Resonance Direct Thrombus Imaging for diagnostic management of suspected pelvic vein thrombosis during pregnancy

The Tethys study is a prospective cohort study that will primarily focus on pregnant women with clinically suspected DVT, a high pre-test probability as determined by the LEFt criteria, a positive D-dimer test but negative single CUS. These patients who are thus suspected of pelvic vein thrombosis, will be subjected to MRDTI within 48 hours of clinical presentation and initial diagnostic testing. Moreover, a small number of patients with 0 or 1 LEFt points in combination with a normal D-dimer test will be subjected to MRDTI as well. In the former patient category, MRDTI will be applied as definite diagnostic test, and patients will be treated based on the result of the MRDTI. In the latter patient category, MRDTI will only be read post-hoc, and its results will not influence the therapeutic management of the patient, since DVT has been ruled out based on the initial tests performed. All patients will be followed for a 90-day (+/-7 days) period for the occurrence of symptomatic VTE as part of the LEAD study.

The Tethys study will be performed in close collaboration with the LEAD study (NCT02507180), a running prospective cohort diagnostic management study in pregnant women with suspected DVT. The primary outcome of this study is to assess the number of VTE events, i.e. any DVT (distal or proximal), pulmonary embolism ([PE] sub-segmental or greater PE), or death potentially attributable to VTE, during the three-month follow-up in those patients left untreated for DVT on the basis of an "unlikely" LEFt score (0 or 1 points) and a negative D-dimer test result. This study aims to include 366 patients to ensure that the lower bound of the 95% confidence interval for the failure rate of the diagnostic strategy is less than 3% (3/300; 1% (95% CI: 0.3 to 2.9%) assuming a point estimate of a 3-month VTE risk of 1% in patients left untreated after completion of the initial diagnostic strategy. In this collaboration, the data of both studies will be combined for the calculation of the main outcomes of LEAD, being secondary outcome 2 and 3 of the Tethys study.

We hypothesize that DVT can be safely ruled out by the LEFt rule in combination with the D-dimer test in 5-10% of pregnant women, and that a normal MRDTI safely rules out isolated pelvic vein thrombosis. We hypothesize that 7-10% of performed MRDTI’s in the patients with high pre-test probability, abnormal D-dimer test but normal CUS will show isolated pelvic vein thrombosis, while MRDTI is negative in the patients in whom DVT is ruled out without imaging

All patients will be followed for 3 months.

MRDTI as decisive diagnostic test in preganant patients with suspected isolated pelvic vein thrombosis