The relationships between markers of pregnancy planning and pre-pregnancy care and adverse outcomes (early pregnancy loss, major congenital anomaly and perinatal death) were examined in 423 singleton pregnancies in women with pre-gestational type I diabetes mellitus. Pregnancy planning and markers of pre-pregnancy care were associated with reduced risks of adverse pregnancy outcomes. 'Documentation of achievement of an optimal haemoglobin A1c prior to discontinuation of contraception' was the marker associated with the lowest rate of adverse outcome (OR 0.2; 95% CI 0.06-0.67) and might serve as an appropriate definition of pre-pregnancy care for research and audit purposes.