Pre-eclampsia is a potentially life-threatening, placenta-associated disease that affects 3% of pregnancies. Aspirin treatment started early in pregnancy reduces the risk of pre-eclampsia but recent guidelines call for prophylactic treatment of 1 in 10 normal pregnancies based on a screening procedure. The problem is the paucity of data on the potential long-term effects, lack of maternal safety data, and surprisingly, insufficient knowledge on the mechanism behind the beneficial effects of aspirin. We will use advanced epidemiological methods to investigate potential risks of aspirin in the Danish registries and in a unique source of prenatal ultrasound data. Outcome include maternal postpartum haemorrhage, foetal growth, and neurodevelopmental offspring outcomes. To corroborate the epidemiological findings and to provide new biological insight in placental biology, we will perform Next Generation Sequencing on placental tissue from unexposed and aspirin exposed pregnancies.