BACKGROUND: Clinical trials of interventions for preventing malaria in pregnancy often use measures of malaria at delivery as their primary outcome. Although the objective of these interventions is to improve birth outcomes, data on associations between different measures of malaria at delivery and adverse birth outcomes are limited. METHODS: Data came from 637 Ugandan women enrolled in a randomized controlled trial of intermittent preventive treatment of malaria in pregnancy. Malaria at delivery was detected using peripheral and placental blood microscopy, placental blood loop-mediated isothermal amplification (LAMP), and placental histopathology. Multivariate analyses were used to estimate associations between measures of malaria at delivery and risks of low birth weight (LBW), small for gestational age (SGA), and preterm birth (PTB). RESULTS: Detection of malaria parasites by microscopy or LAMP was not associated with adverse birth outcomes. Presence of malaria pigment detected by histopathology in ≥30% of high-powered fields was strongly associated with LBW (adjusted risk ratio [aRR] = 3.42, P = .02) and SGA (aRR = 4.24, P < .001) but not PTB (aRR = 0.88, P = .87). CONCLUSIONS: A semiquantitative classification system based on histopathologically detected malaria pigment provided the best surrogate measure of adverse birth outcomes in a high-transmission setting and should be considered for use in malaria in pregnancy intervention studies.