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The letter of Prefumo et al,1Prefumo F. Frusca T. Valensise H. Acetylsalicylic acid in pregnant women with chronic hypertension.Am J Obstet Gynecol. 2018; 218: 463-464Abstract Full Text Full Text PDF Scopus (1) Google Scholar raises 3 issues. First, the necessary dose of aspirin, the gestational age at onset of therapy, and the target condition for prevention, preterm vs term preeclampsia (PE). Second, the best method of selecting women at high risk for preterm PE who would benefit from use of aspirin. Third, should women with chronic hypertension be treated with aspirin? In the Aspirin for Evidence-Based Preeclampsia Prevention trial, use of aspirin (150 mg/d) vs placebo from 11-14 until 36 weeks’ gestation was associated with reduction in the incidence of preterm PE by 62% (95% confidence interval, 26–80%), but had no significant effect on the incidence of term PE.2Rolnik D.L. Wright D. Poon L.C. et al.Aspirin versus placebo in pregnancies at high risk for preterm preeclampsia.N Engl J Med. 2017; 377: 613-622Crossref PubMed Scopus (1093) Google Scholar A meta-analysis of trials on the prophylactic use of aspirin reported reduction in incidence of preterm PE by 67% (95% confidence interval, 43–81%), provided the daily dose was ≥100 mg and onset of therapy was ≤16 weeks; aspirin had no significant effect on incidence of term PE.3Roberge S. Bujold E. Nicolaides K.H. Aspirin for the prevention of preterm and term preeclampsia: systematic review and metaanalysis.Am J Obstet Gynecol. 2018; 218: 287-293Abstract Full Text Full Text PDF PubMed Scopus (283) Google Scholar The traditional method of identifying women at high risk of PE is based on a series of factors from demographic characteristics and medical history, including chronic hypertension; however, the performance of this method is poor, with detection of about 40% of cases of preterm PE, at screen-positive rate of 10%. The method advocated by the Fetal Medicine Foundation is use of Bayes theorem to combine maternal factors with biomarkers (mean arterial pressure, uterine artery pulsatility index, and serum placental growth factor) to determine the patient-specific risk for preterm PE; with this method the detection rate is 75%, at screen-positive rate of 10%.4O’Gorman N. Wright D. Syngelaki A. et al.Competing risks model in screening for preeclampsia by maternal factors and biomarkers at 11-13 weeks’ gestation.Am J Obstet Gynecol. 2016; 214: 103.e1-103.e12Abstract Full Text Full Text PDF PubMed Scopus (320) Google Scholar In screening for trisomy 21 it is now accepted that the best approach of selecting the high-risk group in need of further investigation is use of Bayes theorem to combine maternal age with biomarkers to determine the patient-specific risk, rather than use of arbitrary cut-offs in maternal age or biomarker levels. In this respect, in screening for preterm PE, chronic hypertension should be combined with other maternal factors and biomarkers to determine if the patient-specific risk is high or low. A secondary analysis of data from the Aspirin for Evidence-Based Preeclampsia Prevention trial demonstrated that there was no evidence of heterogeneity in the beneficial effect of aspirin in reducing the incidence of preterm PE in subgroups defined according to maternal age, body mass index, racial origin, method of conception, smoking, family history of PE, obstetrical history, and pre-existing medical conditions, except for chronic hypertension, where aspirin was not useful.5Poon L.C. Wright D. Rolnik D.L. et al.Aspirin for Evidence-Based Preeclampsia Prevention trial: effect of aspirin in prevention of preterm preeclampsia in subgroups of women according to their characteristics and medical and obstetrical history.Am J Obstet Gynecol. 2017; 217: 585.e1-585.e5Abstract Full Text Full Text PDF Scopus (114) Google Scholar Aspirin was also not useful in reducing the incidence of term PE in either patients with or without chronic hypertension. Guidelines should be revised to reflect recent scientific evidence that the target of screening should be preterm rather than all PE, the best way to identify the high-risk group is by a combination of maternal factors and biomarkers, aspirin should be started at ≤16 weeks’ gestation, and the daily dose should be ≥100 mg. Acetylsalicylic acid in pregnant women with chronic hypertensionAmerican Journal of Obstetrics & GynecologyVol. 218Issue 4PreviewWe read with interest the subgroup analysis of the Aspirin for Evidence-Based Preeclampsia Prevention (ASPRE) trial published by Poon and colleagues,1 which gives further insight on the impressive results of the ASPRE trial. Poon et al1 discuss in detail the finding that, in women with chronic hypertension, identified as at high risk of preeclampsia according to the first-trimester Fetal Medicine Foundation prediction model, aspirin may not be useful in the prevention of preterm preeclampsia. This is also in accordance with a previous meta-analysis of individual patient data, which included trials using variable doses of aspirin started at variable gestational ages. Full-Text PDF