The purpose of this report is to describe the current state of research and practice of maternal-fetal surgical procedures; the report does not offer guidance on whether or when such procedures are appropriate. Congenital abnormalities that can be repaired prenatally occur in a small percentage of full-term births, and because of advances in imaging techniques such as ultrasound, many more congenital abnormalities are being diagnosed in utero. As these abnormalities are increasingly frequently recognized prior to delivery, maternal-fetal surgical procedures have emerged as a potential option for treating some of these defects. Although postnatal intervention is best for most fetal abnormalities (particularly in light of risks associated with in utero surgeries), for a few conditions, the fetus' condition can deteriorate so rapidly in the womb as to make early intervention necessary either to avoid death or substantially higher morbidity after birth. Substantial questions remain about both the safety and efficacy of fetal surgical corrections. In some cases, the natural history of the conditions is poorly understood, making comparisons to no treatment or postnatal intervention difficult. In addition, comparisons of fetal versus postnatal surgery must consider the safety of the mother, yet limited comparative data exist. The issue is particularly complicated because while congenital defects are relatively common in aggregate, individual congenital abnormalities occur infrequently, making effective study very difficult. Ongoing trials are evaluating some of the most common fetal surgeries. The goal of this brief is to describe the current state of literature and practice of maternal-fetal surgical procedures for seven congenital abnormalities ranked of high importance by stakeholders: Sacrococcygeal teratoma; Congenital diaphragmatic hernia; Thoracic lesions: congenital cystic adenomatoid malformation and bronchopulmonary Sequestration; Obstructive uropathy; Myelomeningocele; Twin-twin transfusion syndrome; Cardiac malformations. The key questions for this brief were as follows: Key Question 1. a. What fetal diagnoses are currently treatable with a maternal-fetal surgical procedure? For each fetal diagnosis that is potentially treatable with a maternal-fetal surgical procedure, what is the annual number of fetuses that could potentially benefit from the procedure? b. What maternal-fetal surgical procedures are done in the United States? What is an estimate of the number of hospitals that perform each procedure and utilization of each procedure? c. For each fetal diagnosis, which procedures or techniques are used? d. For each maternal-fetal surgical procedure, what anesthesia is used? What are the potential harms to the fetus and mother from the anesthesia? e. For each fetal diagnosis, what are the alternatives? For each fetal diagnosis, what are the theoretical advantages and disadvantages (including potential safety issues and harms to both the mother and fetus) of maternal-fetal surgical procedures relative to the alternatives? f. What training programs exist for maternal-fetal surgical procedures? What special requirements are needed in hospitals that perform fetal surgical procedures? Key Question 2. Perform a systematic literature scan on studies on the use and safety of maternal-fetal surgical procedures for the selected conditions, with a synthesis of: a. Operational definition of fetal diagnoses b. Type of procedure c. Maternal inclusion criteria d. Training of providers of specialized expertise and equipment in the study hospital(s) e. Study design or size/country or setting f. Comparator used (if any) g. Length of followup h. Outcomes measured for both fetus and mother i. Adverse events /harms/safety issues reported for both fetus and mother.