Rib fracture. The infant was G3P1, with a gestational age of 30+1 weeks and a birth weight of 1,370 g. The infant was born by Cesarean section due to placental abruption. After birth, the infant suffered from various diseases, such as respiratory distress syndrome, pneumonia, atelectasis, and calcium and phosphorus metabolism disorder, which was diagnosed as metabolic bone disease. Forty days after birth, an ultrasound examination found that the infant had a fracture in the fifth rib on the left side.