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Key Points: Question: In pregnancies complicated by anhydramnios due to fetal bilateral renal agenesis, do serial amnioinfusions instituted before 26 weeks' gestation mitigate lethal pulmonary hypoplasia in neonates? Findings: In this nonrandomized clinical trial, 82% of live-born infants survived to 14 days of life or longer and placement of dialysis access, but longer-term neonatal survival was reduced. Serial amnioinfusions were not associated with severe maternal complications. Meaning: Prenatal serial amnioinfusions can mitigate neonatal lethal pulmonary hypoplasia in neonates with bilateral renal agenesis, but infants face substantial morbidity independent of lung function. Importance: Early anhydramnios during pregnancy, resulting from fetal bilateral renal agenesis, causes lethal pulmonary hypoplasia in neonates. Restoring amniotic fluid via serial amnioinfusions may promote lung development, enabling survival. Objective: To assess neonatal outcomes of serial amnioinfusions initiated before 26 weeks' gestation to mitigate lethal pulmonary hypoplasia. Design, Setting, and Participants: Prospective, nonrandomized clinical trial conducted at 9 US fetal therapy centers between December 2018 and July 2022. Outcomes are reported for 21 maternal-fetal pairs with confirmed anhydramnios due to isolated fetal bilateral renal agenesis without other identified congenital anomalies. Exposure: Enrolled participants initiated ultrasound-guided percutaneous amnioinfusions of isotonic fluid before 26 weeks' gestation, with frequency of infusions individualized to maintain normal amniotic fluid levels for gestational age. Main Outcomes and Measures: The primary end point was postnatal infant survival to 14 days of life or longer with dialysis access placement. Results: The trial was stopped early based on an interim analysis of 18 maternal-fetal pairs given concern about neonatal morbidity and mortality beyond the primary end point despite demonstration of the efficacy of the intervention. There were 17 live births (94%), with a median gestational age at delivery of 32 weeks, 4 days (IQR, 32-34 weeks). All participants delivered prior to 37 weeks' gestation. The primary outcome was achieved in 14 (82%) of 17 live-born infants (95% CI, 44%-99%). Factors associated with survival to the primary outcome included a higher number of amnioinfusions (P =.01), gestational age greater than 32 weeks (P =.005), and higher birth weight (P =.03). Only 6 (35%) of the 17 neonates born alive survived to hospital discharge while receiving peritoneal dialysis at a median age of 24 weeks of life (range, 12-32 weeks). Conclusions and Relevance: Serial amnioinfusions mitigated lethal pulmonary hypoplasia but were associated with preterm delivery. The lower rate of survival to discharge highlights the additional mortality burden independent of lung function. Additional long-term data are needed to fully characterize the outcomes in surviving neonates and assess the morbidity and mortality burden. Trial Registration: ClinicalTrials.gov Identifier: NCT03101891 This prospective, nonrandomized clinical trial assesses neonatal outcomes after serial amnioinfusions initiated before 26 weeks' gestation to mitigate lethal pulmonary hypoplasia in pregnancies complicated by bilateral renal agenesis. [ABSTRACT FROM AUTHOR]