This thesis describes the results of the LEMMoN study, a nationwide prospective cohort study into severe maternal morbidity in the Netherlands in which all hospitals in the Netherlands participated. The main objectives of the study were to assess incidence, case fatality rate, risk factors and substandard care in severe maternal morbidity in the Netherlands. Cases of severe maternal morbidity were collected during a two-year period. All pregnant women in the Netherlands in the same period acted as reference cohort (n=371,021). Special attention was paid to the ethnic background. Substandard care was assessed in selected cases during audit meetings. Severe maternal morbidity was reported in 2552 cases, overall incidence being 7.1 per 1000 deliveries. Incidences of ICU admission, uterine rupture, eclampsia and major obstetric haemorrhage were 0.24%, 0.06%, 0.06% and 0.45% per 1000, respectively. Non-Western immigrant women had a 1.3 fold increased risk of severe maternal morbidity as compared with Western women. Jehovah__s witnesses had a 3.1-fold increased risk. Overall case fatality rate was 1 in 53. Substandard care was found in 80% of assessed cases during clinical audit. Since substandard care was found in the majority of assessed cases, reduction of severe maternal morbidity seems a mandatory challenge.ZonMW Matty Brand FoundationUBL - phd migration 201