Recurrent pregnancy loss (RPL) is a poorly understood condition that comes with many uncertainties, both for affected couples and healthcare providers. Important goals are to provide answers to these couples and to improve their pregnancy outcomes. To achieve this, we need a better understanding of contributing and predictive factors. Until now, the male role in RPL has been underexposed. In this thesis, we aimed to expand our knowledge regarding the ‘forgotten father’ in RPL. We have found strong clues that in RPL, male contribution really matters.The main conclusions are that advanced paternal age and paternal smoking are associated with an increased risk of pregnancy loss, that inclusion of paternal factors into a prediction model improves the accuracy of predicting ongoing pregnancy after RPL, and that impaired immunomodulatory effects of seminal plasma may play a role in RPL. At the same time, our studies have led to new questions and uncovered new challenges, which are excellent opportunities for further research. Stichting Oranjekliniek, Department of Gynaecology and Obstetrics of the Leiden University Medical Center, Moeders voor Moeders, Goodlife Pharma, Canon Medical Systems Nederland, Hellp Stichting, Castor EDC, ChipSoftLUMC / Geneeskund
