The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Maternal Fetal Medicine Units Network was set up in 1986 to conduct major randomized trials and observational studies in maternal-fetal medicine. Two observational studies – the Cesarean Registry and the Assessment of Perinatal Excellence (APEX) study – together provide detailed obstetric and delivery information on 192,000 women, with a particular focus on maternal morbidity. The purpose of the Cesarean Registry was to determine the safety and success of trial of labor in women with a prior cesarean delivery. The purpose of APEX was to evaluate measures of quality of care. In both studies, detailed information on maternal morbidity and patient characteristics were collected. By harmonizing these two datasets we can provide a rich resource for researchers in high risk obstetrics. The NICHD also supported the Management of Myelomeningocele Study (MOMS), a ground-breaking trial of surgical repair of the spina bifida defect before the baby is born versus the usual postnatal surgical repair. In addition, MOMS2, a follow-up study of the children at 6 to 10 years old has recently been completed. The trial and the follow-up study serve as a model for other trials in the area of maternal-fetal surgery where both the mother and fetus undergo a procedure before birth. We propose to create a linked dataset, which while preserving privacy, will provide researchers with a unique resource of longitudinal data in the field of maternal-fetal therapy. As the data coordinating center for both of these initiatives (MFMU and MOMS) we will make the carefully curated data with appropriate metadata available to the NICHD Data and Specimens Hub in response to PAR-20-064 ‘Archiving and Documenting Child Health and Human Development Data Sets’.