Neoreviews 20 (1): e12-e24, 2019. doi: 10.1542 / neo.20 - 1-e12 Diagnosis of Meconium Ileus Plain x-rays If positive, tests for cystic fibrosis Prenatal ultrasonography can detect changes in utero suggestive of cystic fibrosis and meconium ileus (eg, dilated bowel, polyhydramnios), but these changes are not specific.