Bronchopulmonary dysplasia is a chronic lung disease of babies, which most commonly develops in the first 4 weeks after birth and most often affects babies born at least 4 weeks before term. The lungs do not work properly in bronchopulmonary dysplasia (BPD) and the baby has trouble breathing, needs extra oxygen, and may need help from a ventilator (breathing machine). The risk of BPD increases as the baby’s weight and time in the mother’s uterus decreases. Today, most babies with BPD (9 out of 10) weigh 1,500 grams (about 3 and a half pounds) or less at birth. Babies born weighing less than 1,000 grams (about 2 pounds) are at very high risk. About 1 out 3 of these gets BPD.