AbstractIntroductionLung hypoplasia and pulmonary arterial hypertension in congenital diaphragmatic hernia lead to a high perinatal mortality. Although sustained fetoscopic tracheal occlusion (TO) improves lung development, a major side effect is abnormal pneumocyte differentiation. This study evaluated the potential ability of intratracheal retinoic acid (RA) administration to reduce adverse effects of sustained TO in a rabbit model of diaphragmatic hernia.MethodsA left diaphragmatic defect was created on day 23 in time‐dated pregnant rabbits. On day 28, the same rabbits underwent sham surgery or TO, with an injection of empty or RA‐loaded liposomes. On day 30, the fetuses were harvested, and the lungs were processed for histology, immunohistochemistry, and gene expression quantification.ResultsA tracheal RA injection at the time of TO had no effect on the lung‐to‐body‐weight ratio, radial alveolar count or lung connective tissue composition. Retinoic acid plus TO had synergic effects on vascular measurements, proportional medial thickness, and endothelin‐1 receptor type‐A gene expression. The most noticeable effect was recovery of normal pneumocyte differentiation.ConclusionRetinoic acid plus TO prevented abnormal pneumocyte differentiation and seemed to have a beneficial effect on pulmonary vascularization.