The Effect of Low-Dose Aspirin on Platelet Function During Pregnancy Compared to Placebo: an Explorative Study.

Objectives: To evaluate the effect of aspirin 80 mg compared to placebo on platelet function tests in the second and third trimester of pregnancy. Study design: An explorative study was performed to assess laboratory platelet function in a subpopulation of the APRIL trial: a randomized double-blind trial comparing aspirin 80 mg once daily to placebo for the prevention of recurrent preterm birth. Platelet function was measured between 18 and 22, and between 28 and 32 weeks gestational age with three platelet function tests: VerifyNow (R), Chronolog light transmission aggregometry (Chronolog LTA) and serum thromboxane B2 (TxB(2)). Medication adherence was evaluated by pill counts, self-reported diaries and structured interviews. Results: We included 11 women, six in the aspirin and five in the placebo group. In women receiving aspirin, platelet function was significantly lower compared to women receiving placebo for all three tests: VerifyNow (R) Aspirin Reaction Units (450.5 vs 648.0, p = 0.017); Chronolog LTA (9.5% vs 94.5%, p = 0.009); serum TxB(2) levels (11.9 ng/mL versus 175.9 ng/mL, p = 0.030). For all three tests, platelet function did not differ between the second and third trimester of pregnancy in the aspirin group. In the placebo group, serum TxB(2) levels were significantly higher in the third trimester. One non-adherent participant in the aspirin group showed results similar to the placebo group. Conclusion: Aspirin 80 mg has a clear inhibitory effect on laboratory platelet function during pregnancy compared to placebo. This effect is similar in the second and third trimester of pregnancy.