[Aspirin and pregnancy in the era of early first-trimester screening: efficacy, indications and maternal-fetal safety].

Apart from calcium supplementation, which is beneficial in women with inadequate intake, low-dose aspirin is the only drug with established efficacy for the primary prevention of preeclampsia. Its mechanism - restoration of the thromboxane A2 / prostacyclin balance through platelet cyclo-oxygenase-1 inhibition - accounts for its efficacy in placental vascular disease, and its benefit depends on a dose of 100 to 160 mg, evening intake and, above all, initiation before 16 weeks. The question is no longer whether it works, but in whom, and whether this can be known early enough. Three early identification strategies have been evaluated in turn. Clinical risk factors, used by the historical trials and then by Anglo-Saxon guidelines, are either too restrictive - a history of preeclampsia by construction excludes nulliparous women - or so broad that up to 85% of women would become eligible. First-trimester uterine artery Doppler, a direct reflection of trophoblastic invasion, offered an attractive pathophysiological rationale; the double-blind randomised trials nevertheless proved negative, including the French PERASTUN trial conducted in 1,104 nulliparous women selected on this criterion alone and treated with 160 mg before 16 weeks (16.0% vs 14.4%), Doppler alone lacking specificity and selecting a population with low absolute risk whose preeclampsia is mostly late - precisely where aspirin has no effect. Combined algorithms, associating maternal factors, mean arterial pressure, Doppler and PlGF, perform better: the ASPRE trial reduced preeclampsia before 37 weeks of gestation by 62%, though part of the benefit arose from women already identifiable by their history; the ongoing French RANSPRE trial randomises the screening strategy itself for the first time. This uncertainty about the target population explains the marked heterogeneity of international guidelines and bears directly on safety: while the fetal profile remains reassuring at antiplatelet doses, recent maternal data, including a French nationwide cohort of 5.8 million pregnancies, show an excess of haemorrhagic complications. Defining whom to treat is the condition for preserving a favourable benefit-risk balance.