Bronchopulmonary dysplasia (BPD) is a chronic lung disease that develops in premature infants, most often those born before 28 weeks of gestation. It happens when a baby’s lungs, still in the early stages of development at birth, are injured by the very treatments needed to keep the baby alive, particularly mechanical ventilation and supplemental oxygen. Among extremely premature infants in the United States, between 32% and 45% develop BPD, making it one of the most common serious complications of prematurity.
Why Premature Lungs Are Vulnerable
A full-term pregnancy lasts about 40 weeks. The tiny air sacs in the lungs, called alveoli, don’t finish forming until the final weeks of pregnancy and continue developing after birth. When a baby is born months early, the lungs have far fewer air sacs, and the blood vessels that surround them are equally immature. This means the lungs can’t efficiently exchange oxygen and carbon dioxide on their own.
At a cellular level, BPD disrupts the growth signals that tell the lungs to keep building new air sacs and blood vessels. One of the most important of these signals is a protein that promotes blood vessel growth. In infants who develop severe BPD, levels of this protein are significantly reduced. When blood vessel growth stalls, air sac development stalls with it, because the two processes are tightly linked. The result is “alveolar simplification,” meaning the lungs end up with fewer, larger air sacs instead of the millions of small ones needed for efficient breathing. Less surface area means less ability to absorb oxygen.
What Causes the Lung Injury
The primary culprits are mechanical ventilation and oxygen therapy, both of which are often necessary to keep extremely premature infants alive but can damage fragile lung tissue in several ways.
- Pressure injury (barotrauma): High ventilation pressures can cause air to leak into the spaces around the lungs, triggering inflammation.
- Volume injury (volutrauma): Inflating the lungs beyond their natural capacity stretches and tears delicate tissue, causes fluid to leak into the air sacs, and draws immune cells into the lungs.
- Collapse injury (atelectrauma): The repeated opening and closing of air sacs that haven’t fully inflated causes shearing forces that damage the lung lining.
- Inflammation (biotrauma): All of the above trigger an inflammatory cascade that further injures the lungs and interferes with normal development.
Oxygen itself, while life-saving, is toxic to immature lung tissue in high concentrations. Prolonged exposure generates harmful molecules that damage cells and amplify inflammation. Infections, both before and after birth, also contribute. A baby whose mother had an infection of the membranes surrounding the uterus faces higher risk, as does any premature infant who develops a postnatal infection in the hospital.
How BPD Is Diagnosed and Graded
Doctors typically assess for BPD at 36 weeks postmenstrual age, which is 36 weeks from the start of the mother’s last menstrual period, not 36 weeks after birth. At that point, they evaluate how much respiratory support the baby still needs. A chest X-ray showing characteristic lung changes confirms the diagnosis.
BPD is classified into three grades based on how much oxygen and what type of breathing support the infant requires:
- Grade I (mild): The baby needs low levels of supplemental oxygen or minimal breathing support.
- Grade II (moderate): The baby requires higher oxygen concentrations or more significant support such as continuous positive airway pressure.
- Grade III (severe): The baby needs both high oxygen levels and mechanical ventilation, or very high oxygen through any delivery method.
An international effort published in 2025 in the journal Pediatrics emphasized that BPD definitions should be severity-based and should predict long-term respiratory outcomes, not just describe the baby’s status at one moment. Despite this push, the most commonly used definition in clinical practice remains the one established in 2001, and there is still notable variation in how different hospitals classify the condition.
Pulmonary Hypertension: A Serious Complication
About 25% of infants with moderate to severe BPD develop high blood pressure in the blood vessels of the lungs, a condition called pulmonary hypertension. This happens because the same disrupted growth signals that prevent normal air sac development also cause the lung’s blood vessels to be fewer in number and abnormally constricted. The heart has to work much harder to push blood through these narrowed vessels, and over time this can strain the right side of the heart. Pulmonary hypertension substantially increases mortality risk in babies with BPD and is one of the complications that neonatal teams monitor most closely.
Treatment in the NICU
There is no single cure for BPD. Treatment focuses on supporting the baby’s breathing while minimizing further lung injury and giving the lungs time to grow.
Caffeine is one of the most widely used preventive treatments. Starting it within the first two days of life reduces the combined risk of BPD and death compared to starting later. It works by stimulating the baby’s breathing drive, reducing the need for mechanical ventilation. Nearly all extremely premature infants receive caffeine as a standard part of their care.
When babies remain dependent on a ventilator, doctors may use a short course of corticosteroids to reduce lung inflammation and help get the baby off the machine. Current guidelines from the American Academy of Pediatrics recommend using the lowest effective dose for a short, predefined period. High doses are not recommended because of concerns about effects on brain development. If there’s no improvement within 72 hours, continuing the medication is not advised.
Nutrition plays a critical role as well. Babies with BPD burn significantly more calories just to breathe, yet their fluid intake is often restricted to prevent fluid from accumulating in the lungs. This creates a challenging balance. Adequate protein and calorie intake during the first weeks of life is essential because poor early nutrition is associated with worse lung outcomes. Feeding strategies are carefully adjusted to pack enough energy into limited volumes of milk or formula.
Many infants with moderate to severe BPD go home on supplemental oxygen delivered through a nasal cannula. Some need it for weeks, others for months, and a smaller number for more than a year. Parents learn to manage oxygen equipment, monitor their baby’s oxygen levels, and watch for signs of respiratory distress.
Long-Term Respiratory Health
BPD is not something children simply outgrow. While many improve significantly during the first few years of life, the condition leaves lasting marks on lung function that can persist into adulthood.
Research tracking adults who had BPD as infants reveals measurably reduced lung function compared to people born at term, people born preterm without BPD, and even people with asthma. In one study, 27% of adults with a history of BPD had airway obstruction below the normal threshold, compared to less than 5% in both the preterm-without-BPD group and the asthma group. Adults with BPD history also show signs of small airway disease and air trapping, meaning air gets stuck in the lungs during exhalation, and reduced gas diffusing capacity, meaning the lungs are less efficient at moving oxygen into the bloodstream.
These findings look similar to chronic obstructive pulmonary disease (COPD), a condition typically associated with decades of smoking. Researchers now recognize that early life events, including premature birth and BPD, are meaningful risk factors for developing chronic airway obstruction later in life, even in people who have never smoked. An estimated 20% to 25% of all COPD patients have no smoking history, and neonatal lung injury is increasingly recognized as one explanation.
For children and adults with a history of BPD, avoiding cigarette smoke, air pollution, and respiratory infections is especially important. Regular follow-up with a pulmonologist can help track lung function over time and catch any decline early. Exercise is generally encouraged and beneficial, though some individuals may notice more shortness of breath during intense activity than their peers.