Objective: Verify that resistance to aspirin may have an impact on pregnancy and neonatal outcome.
Methods: We enrolled 43 pregnant women, aged 30.7 ± 4.0 years regularly taking 75 mg of aspirin daily and 32 (aged 30.8 ± 4 years) pregnant women not receiving aspirin who served as control group. Laboratory tests were performed at 18 to 22 weeks of gestation, 28 to 32 weeks of gestation and 16 to 32 weeks after delivery. Resistance to aspirin was defined as urinary 11-dehydrothromboxane B2 (u11-dTXB2) concentrations in the highest quartile and additionally, as the resistance index (RI) calculated for each woman, defined as the difference between u11-dTXB2 concentration of each woman treated with aspirin and the median value at the same time point measured in the control group.
Results: Women taking aspirin in the highest quartile of u11-dTXB2 delivered prematurely (35.8±3.4 vs 38.1±1.7 weeks, p=0.02). Delivery of small for gestational age (SGA) newborns (p=0.003) as well as fetal distress (p=0.014) and preeclampsia (p=0.003) occured more frequently in aspirin-resistant women. Resistance to aspirin based on the RI value was also associated with higher prevalence of preeclampsia (p=0.02) and SGA newborns delivery (p=0.01). The two groups resistant to ASA designed on the basis of both (RI and u11-dTXB2 urine levels) methods compared with ASA sensitive group differed in frequency of SLE prevalence.
Conclusion: Aspirin resistance may be associated with increased risk of adverse pregnancy outcomes including preeclampsia, premature delivery and delivery of SGA newborns.