The aim of this study is to examine whether treatment with 75 mg aspirin daily compared with placebo could reduce the risk for a new miscarriage. The treatment starts when the pregnancy is detected on transvaginal ultrasound (around gestational week 6+) and continues to week 35/36. The study is a single center, randomized, placebo-controlled, double blind and stratified for age. 400 participants with the diagnosis idiopathic recurrent abortion are enrolled, 200 in each arm aspirin / placebo.

Inclusion Criteria:

• recurrent abortion (≤ 3 consecutive abortions in first trimester)
• unknown etiology after work-up
• willingness to be randomized

Exclusion Criteria:

• previous participation in the study
• known cause of recurrent abortion, requiring specific management
• age ≥ 40
• BMI above 35
• IVF pregnancy if the reason for IVF was recurrent spontaneous abortion
• ongoing treatment with aspirin for other reason
• Sjoegren syndrome