Low-dose ASA response using the PFA-100 in women with high-risk pregnancy

To study the platelet function response to low-dose ASA with the Platelet Function Analyzer (PFA-100) in pregnant women and to identify maternal characteristics associated with non-responsiveness.

We conducted a prospective cohort study involving 87 pregnant women on ASA. The platelet function response to ASA was measured as the closure time obtained with epinephrine cartridges (CT-EPI) by the PFA-100. Non-response to ASA was defined as a CT-EPI < or =150 seconds after four weeks of therapy. Non-responders were given an escalating dose of ASA and their CT-EPI was tested again.

After four weeks of enteric-coated ASA 81 mg daily, 25/87 women (28.7%) were non-responders (95% CI 16.1 to 41.4). Among these women, a CT-EPI < or =150 seconds was found in 8/24 women (33.3%) after another four weeks of alternating ASA 81 mg and 162 mg daily. After a further four-week course of ASA 162 mg daily, a CT-EPI < or =150 seconds was found in 3/6 women (50.0%). Among the women who initially responded and who were reassessed at 24-32 weeks of pregnancy, the CT-EPI was < or =150 seconds in 9/36 (25.0%). There was no statistical difference in maternal characteristics between ASA responders and non-responders.

A significant number of pregnant women showed a lack of platelet function response to ASA 81 mg that was in most cases overcome with higher dosing. Furthermore, the prevalence of non-responsiveness increased with advancing pregnancy.