title: Management of pregnant women with mechanical heart valve prosthesis: thromboprophylaxis with low molecular weight heparin.
abstract: BACKGROUND
  Pregnancy increases the risk of mechanical heart valve (MHV) thrombosis. Warfarin is protective, but implies risks to the fetus. Unfractionated heparin (UFH) is less effective but does not harm the fetus. In general, anticoagulation is more stable and predictable with low molecular weight heparin (LMWH) than with UFH.
  
  
  METHODS
  Retrospective study of 12 pregnancies with MHV; 6 in aortic, 4 in mitral, and 2 in both positions, treated with therapeutic doses of subcutaneous LMWH twice daily throughout pregnancy. Doses were adjusted using anti-Xa monitoring. The frequency of thrombo-embolism with various anticoagulation regimes was calculated based on a literature review.
  
  
  RESULTS
  Median LMWH dose was 15500 IU/24 h, range 10000-20000 IU/24 h; median dose 257 IU/kg/24 h. Median peak LMWH in blood plasma ranged 0.54-0.92 anti-Xa U/mL. Thromboembolism developed in two women with aortic MHV despite LMWH levels in target range. One had systemic embolic episodes; in the other woman valve thrombosis was successfully thrombolysed. Both had initially received subtherapeutic doses. Thrombo-embolism was not observed in ten pregnancies treated as recommended. The pregnancies resulted in thirteen healthy babies; eight delivered by Cesarean section. Bleeding occurred in two women after Cesarean section due to preeclampsia.
  
  
  CONCLUSIONS
  Treatment with adjusted therapeutic doses of LMWH was successful in 10 of 12 pregnancies, and was not associated with fetal complications. Thromboembolism occurred in two pregnancies, possibly attributed to subtherapeutic doses of LMWH during the initial 3 weeks. Compared to UFH prophylaxis, therapeutic doses of LMWH appears to be more efficacious.
authors.affiliation: Department of Hematology, Aker University Hospital, Oslo, Norway. ulrich.abildgaard@medisin.uio.no
authors.forename: Ulrich
authors.initials: U
authors.lastname: Abildgaard
authors.forename: Per Morten
authors.initials: PM
authors.lastname: Sandset
authors.forename: Jens
authors.initials: J
authors.lastname: Hammerstrøm
authors.forename: Finn Tore
authors.initials: FT
authors.lastname: Gjestvang
authors.forename: Arnljot
authors.initials: A
authors.lastname: Tveit
mesh_terms: D000328:Adult; D000925:Anticoagulants / Q000008:administration & dosage; D005260:Female; D006350:Heart Valve Prosthesis / Q000009:adverse effects*; D006495:Heparin, Low-Molecular-Weight / Q000008:administration & dosage*; D006801:Humans; D011247:Pregnancy; D011249:Pregnancy Complications, Cardiovascular / Q000517:prevention & control*; D012189:Retrospective Studies; D013927:Thrombosis / Q000209:etiology* / Q000517:prevention & control*; D016896:Treatment Outcome
chemical_list: D000925:Anticoagulants; D006495:Heparin, Low-Molecular-Weight