Anticoagulation in Pregnant Women With Mechanical Valves

Study Questions:

What are the risks of advanced maternal and fetal outcomes in pregnant women with mechanical heart valves (MHVs) receiving different methods of anticoagulation?


The authors performed a meta-analysis of 18 publications through June 5, 2016. Included maternal outcomes included death, thromboembolism, and valve failure. Included fetal outcomes included spontaneous abortion, death, and congenital defects. The studies explored the use of one or more of the following anticoagulants: 1) a vitamin K antagonist (VKA) throughout pregnancy, 2) low molecular weight heparin (LMWH) throughout pregnancy, 3) LMWH for the first trimester followed by VKA (LMWH + VKA), or 4) unfractionated heparin for the first trimester followed by a VKA (UFH + VKA).


Eight hundred pregnancies from 18 publications were included in the analysis. Composite maternal risk was lowest with VKA (5%) as compared to LMWH (16%; ratio of average risks [RAR], 3.2; 95% confidence interval [CI], 1.5-7.5), LMWH + VKA (16%; RAR, 3.1; 95% CI, 1.2-7.5), and UFH + VKA (16%; RAR, 3.1; 95% CI, 1.5-7.1). Composite fetal risk was higher with VKA (39%) as compared to LMWH (13%; RAR, 0.3; 95% CI, 0.1-0.8). Similar composite fetal risk was seen with LMWH + VKA (23%) and UFH + VKA (34%). No significant difference in fetal risk was observed between individuals on ≤5 mg of daily warfarin and those on a LMWH regimen (RAR, 0.9; 95% CI, 0.3-2.4).


The authors concluded that VKA treatment was associated with the lowest risk of adverse maternal outcomes, while LMWH use was associated with the lowest risk of adverse fetal outcomes. The authors also concluded that there were similar fetal risks between women on warfarin ≤5 mg daily and women using LMWH.


Appropriate thromboprophylaxis for pregnant women with MHVs has been a topic of much debate. While the risk of moderate- to high-dose VKA has been well described, this fear has led many pregnant women and clinicians to avoid its use altogether. This meta-analysis provides reassurance that use of low-dose warfarin (≤5 mg daily) can be an equally safe (possibly safer) choice than LMWH for pregnant women with MHVs. This is also supported by the 2014 American Heart Association/American College of Cardiology Guideline for the Management of Patients With Valvular Heart Disease.

Clinical Topics: Anticoagulation Management, Cardiac Surgery, Congenital Heart Disease and Pediatric Cardiology, Prevention, Valvular Heart Disease, Cardiac Surgery and Arrhythmias, Cardiac Surgery and CHD & Pediatrics, Cardiac Surgery and VHD, Congenital Heart Disease, CHD & Pediatrics and Arrhythmias, CHD & Pediatrics and Prevention, CHD & Pediatrics and Quality Improvement

Keywords: Abortion, Spontaneous, Anticoagulants, Heart Defects, Congenital, Heart Valve Diseases, Heart Valve Prosthesis, Heparin, Heparin, Low-Molecular-Weight, Pregnancy, Pregnancy Trimester, First, Primary Prevention, Risk, Thromboembolism, Treatment Outcome, Vitamin K, Warfarin

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