Background: Severe maternal morbidity (SMM) is a key indicator of maternal health. Generally explored without distinction by the timing of the event, it mainly reflects postpartum SMM. Although antepartum (pre-labour) SMM presents specific challenges in its need to optimise the risk-benefit balance for both mother and foetus, its features remain inadequately explored. Objectives: We explored risk factors of antepartum SMM and described adverse delivery and neonatal outcomes associated with antepartum SMM. Methods: We designed a population-based nested case-control study based on data from the EPIMOMS study (119 maternity hospitals of 6 French regions, 2012-2013, N = 182,309 deliveries in the source cohort). This study included all women with antepartum SMM (cases, n = 601) compared to a randomly selected sample of women who gave birth without SMM in the same hospitals (controls, n = 3651). Antepartum SMM risk factors were identified with multivariable logistic regression following imputations for missing data. Results: Antepartum SMM complicated 0.33% (95% confidence interval [CI] 0.30, 0.36) of pregnancies. Antepartum SMM risk factors were maternal age ≥35 years (adjusted odds ratio [OR] 1.55, 95% CI 1.22, 1.97), increased body mass index (OR for 5 kg/m2 increase, 1.24, 95% CI 1.14, 1.36), maternal birth in sub-Saharan Africa (OR 1.80, 95% CI 1.29, 2.53), pre-existing medical condition (OR 2.56, 95% CI 1.99, 3.30), nulliparity (OR 2.26, 95% CI 1.83, 2.80), previous pregnancy-related hypertensive disorders (OR 4.94, 95% CI 3.36, 7.26), multiple pregnancy (OR 5.79, 95% CI 3.75, 7.26), irregular prenatal care (OR 1.86, 95% CI 1.27, 2.72). For women with antepartum SMM, preterm delivery, neonatal mortality and transfer to the neonatal intensive care unit were 10 times more frequent than for controls. Emergency caesarean and general anaesthesia were more frequent in women with antepartum SMM. Conclusions: Antepartum SMM is rare but associated with increased rates of adverse delivery and neonatal outcomes.