IntroductionHepcidin production is normally upregulated by iron stores, and in obesity has been shown to be overexpressed and correlated with low iron status. The increased hepcidin may restrain the iron release from the cells by affecting the expression of ferroportin, which probably associates with the development of diabetes complication. First, we investigate the difference of serum hepcidin and iron parameters between obese and non-obese pregnant women; second, we examine the correlation between serum hepcidin and adverse maternal and neonatal outcomes in pregnant women.Methods and analysisThis is a mono-centre, prospective cohort study with a study (obese) and a control group (non-obese women). In the first trimester, 188 singleton pregnancies will be recruited. Thereof, we expect 75 with a body mass index (BMI) ≥30 kg/m²and 113 with a BMI 18.5–30 kg/m². Serum hepcidin, iron and haematological parameters will be measured at 11–14, 24–28, 32–36 weeks of gestation and at time of delivery. Blood pressure, weight, BMI and smoking status will be examined at all visits. We will assess the composite endpoints adverse maternal outcomes (including pre-eclampsia, gestational hypertension, gestational diabetes mellitus, haemorrhage, placenta abruption) and adverse neonatal outcomes (preterm birth, intrauterine growth restriction, preterm premature rupture of membranes, Apgar score <7 at 5 min, stillbirth, neonatal death).Recruitment has started in April 2019.Ethics and disseminationThis study received ethical approval from the ethics committee in Basel. The results of the study will be published in a peer-reviewed journal, and presented at national scientific conferences.Trial registration numberNCT03792464.