A term infant has initial Apgar scores of 8 and 10 at 1 and 5 minutes. On auscultation of the chest, a heart murmur is audible. There is hepatosplenomegaly. Cataracts of the crystalline lens are noted. The infant is at the 30th percentile for height and weight. Echocardiography shows a patent ductus arteriosus. Which of the following events is the most likely risk factor for the findings in this infant?