A best evidence topic was written according to a structured protocol in order to identify the mode of anticoagulation that has the best safety profile for both the mother and the foetus in pregnant patients with mechanical prosthetic heart valves. A total of 281 papers were identified using the reported search, of which eight represented the best evidence to answer the clinical question. The authors, date, journal, study type, population, main outcome measures and results are tabulated. The reported measures were foetal mortality, maternal mortality,
congenital abnormalities and
embryopathy, and maternal thromboembolic and haemorrhagic complications. The medical orthodoxy has warned of the combination of oral anticoagulation and pregnancy due to the well-documented
warfarin embryopathy. Yet only one of the reported papers identified a greater incidence of foetal aberrations among
warfarin use, with the highest reported rate being 6.4% and two of the assessed papers reporting no
embryopathy at all. Foetal mortality with oral anticoagulation use ranged from 1.52 to 76%. All reported publications demonstrated a superior maternal outcome with
warfarin use, with a range of thromboembolic events from 0 to 10% in comparison with 4 to 48% where
heparin was used. Thus, it is concluded that
warfarin is a more durable
anticoagulant with a better maternal outcome despite it carrying a greater foetal risk. Although, in contrast to previous teaching, the risks of
embryopathy are not the major drawback of oral anticoagulation.
Heparin is consistently less effective, but may be preferred for the superior foetal outcome.
Heparin usage during the first trimester reduces the foetal risk but is still associated with an adverse maternal outcome. While the focus for clinicians looking after pregnant women with mechanical heart valves may be to prevent maternal thromboembolic complications, the overriding concern for many women is to avoid any harm to their unborn child, even when this places their health at risk. Thus women with mechanical heart valves must be fully informed of the risks involved with different anticoagulation for an informed decision to be made.