Aspirin response by PAR4 genotype. Aspirin response as assessed by PAR4 genotype in pregnancy at PFA-100 epinephrine closure time for 106 (A) and 98 (B). (C) Urinary thromboxane (n = 17) with >75% aspirin adherence, visit follow-up 1, 2 to 4 weeks after initiation of 81 mg daily. (D) Urinary thromboxane for 16 patients with >75% aspirin adherence; visit follow-up 2, 28 to 32 weeks gestation. The generalized estimating equation model taking into consideration repeat measures and relevant covariates was not significant for PFA-100 but was significantly different for urinary thromboxane (geometric mean ratio, 2.08 [95% CI, 1.66-2.61]; P < .001).