A 21-year-old woman presents to the emergency room in active labor. She has had no prenatal care, but her last menstrual period was approximately 9 months prior. Her membranes are artificially ruptured, yielding no amniotic fluid. She delivers an 1800-g (4-lb) term infant who develops significant respiratory distress immediately at birth. The first chest radiograph on this infant is shown. After stabilization, the most appropriate next step for this infant is which of the following?

Oligohydramnios can cause a number of serious problems in the infant, including constraint deformities (such as clubfoot) and pulmonary hypoplasia, as shown in the photograph which shows essentially no long development. These infants have usually experienced intrauterine growth retardation and frequently have an associated serious renal abnormality. Ultrasound of the kidneys is important to rule out renal involvement as a cause of the oligohydramnios. None of the other testing would be expected to identify an etiology for the oligohydramnios and pulmonary hypoplasia, although this child's ultimate clinical course might necessitate additional testing. The finding of bilateral renal agenesis is termed Potter sequence.