Low-dose aspirin started in the first-trimester has been associated with a decrease of preeclampsia, fetal growth restriction and preterm birth in high-risk pregnancies. Multiple pregnancies are considered a risk factor for all those adverse outcomes. The main objective of the current trial is to evaluate whether a dose of 80 mg of aspirin is associated with an improvement of birthweight compared to placebo in twin pregnancies.

Twin pregnancies represent approximately 3% of births and are associated with increased risks of complications such as preeclampsia, fetal growth restriction and preterm birth. All of these complications are commonly associated impaired placental function and low birth weight.

Most prophylactic measures tested over the years have failed to prevent these adverse outcomes in twin pregnancies. Since administration of low-dose of aspirin can improve placental function and all these adverse outcomes in high-risk pregnancies, mainly in women with prior adverse outcomes, we suggest that similar benefits could be seen in twins. We are expecting that the administration of low-dose of aspirin starting in the first-trimester in twin pregnancies could lead to an improvement of placental function, a reduction or these adverse perinatal outcomes and therefore to an improvement of birthweight.

Inclusion Criteria:

• Gestational age between 8 0/7 and 13 6/7 weeks
• Twin pregnancy confirmed by ultrasound

Exclusion Criteria:

• One or two negative heart beat
• Previous hypertensive disorder of pregnancy
• Pre-existing hypertension or diastolic blood pressure >90 mmHg at randomization
• Pre-existing nephropathy
• Pre-existing diabetes (type 1 or 2)
• Anaphylactic allergy to lactose
• Known coagulopathy (antithrombin III deficiency, factor V Leiden, antiphospholipid syndrome, the prothrombin mutation, deficiency of protein S or protein C)
• Use of heparin or other anticoagulants.
• Contre-indications to aspirin
• Discordance of crown-rump length greater than 20%.
• Fetal anomalies (cystic hygroma, nuchal translucency > 95th percentile, anencephaly, omphalocele, etc.)
• Previous or current gastric ulcer