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22-07-2009 | Cardiology | Article

LMWH effective for pregnancy mechanical heart valve thromboprophylaxis


Free abstract

MedWire News: Low molecular weight heparin (LWMH) may offer effective thromboprophylaxis for pregnant women with mechanical heart valves, researchers suggest, by balancing the risks for maternal thrombosis and fetal harm.

“Oral anticoagulants (OA) offer the best protection against thrombosis, but their use is associated with an appreciable risk of fetal malformations and pregnancy loss,” explain Ulrich Abildgaard (Aker University, Oslo, Norway) and co-workers.

“Substituting OA with unfractionated heparin (UFH) reduces the risk for fetal damage, but increases the risk of valve thrombosis, even when administered in adjusted doses.”

Following a patient request for alternative thromboprophylaxis following pregnancy loss while using warfarin, the team treated the patient with LMWH, and pregnancy was successful and without complications.

The researchers now report on the outcome of this and 11 other pregnancies (13 infants) in women with aortic (n=6), mitral (n=4), or both types of mechanical heart valves (n=2) who were treated with LMWH throughout their gestation.

Patients were given LMWH twice daily and doses were adjusted using anti-Xa monitoring, with a median dose of 57 IU/kg/24 hours and a median peak LMWH plasma level of 0.54–0.92 anti-Xa U/ml.

As reported in the journal Thrombosis Research, two women with aortic valves developed venous thromboembolism (VTE) despite adequate thromboprophylaxis.

One patient developed aortic valve thrombosis and was treated successfully with alteplase, while the second patient experienced repeated systemic embolism to the lower and upper limbs. Both patients underwent cesarean section and were treated with bridging UFH therapy.

The team calculated the risk for VTE with LMWH treatment throughout pregnancy using their data and other reports to be 7.1%. This compared favorably with historical information used to calculate the risk for VTE with UFH in first trimester followed by OA (10.3%). The lowest risks were with OA throughout (2.4%) and LMWH in first trimester alone (3.6%).

Although OA provides the greatest protection against maternal thrombosis, there is a risk for fetal malformation and then cranial bleeding after week 35, while using

LMWH or UFH in only first trimester, or UFH throughout, reduces risk for fetal malformation but at greater risk for maternal thrombosis, explain Abildgaard et al.

Noting the intermediate risk for VTE with LMWH throughout pregnancy, the team concludes: “In a woman who is unwilling to use OA during her pregnancy, this regimen may be an acceptable alternative provided strict adherence to a high therapeutic dosage regimen.”  

MedWire ( is an independent clinical news service provided by Current Medicine Group, a part of Springer Science+Business Media. © Current Medicine Group Ltd; 2009

By Lynda Williams

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