How Does Congenital Diaphragmatic Hernia Affect Lungs?

It is a common misconception that the lungs in babies with Congenital Diaphragmatic Hernia (CDH) are small solely because the stomach and other abdominal organs are pushing up into the chest. While this physical crowding does play a major role, researchers now understand that lung development in CDH is affected by a “dual-hit” process ^[1]. This means there are actually two distinct challenges (or “hits”) that cause the lungs to be smaller and less developed than expected, a condition doctors call pulmonary hypoplasia ^[2].

The First Hit: Early Developmental Challenges

The “first hit” happens very early in pregnancy, before the diaphragm is even fully formed ^[1]. During this early stage, a developmental change occurs that prevents normal lung growth from the very beginning ^[1].

It is incredibly important to know that you did not cause this. This early change is a random developmental event, not the result of anything you did, ate, or experienced during pregnancy.

Because of this early issue, the tiny tubes (airways) and early lung structures do not branch out as much as they should ^[1]. This first hit affects the cells that make up the lung tissue, meaning the lungs start out smaller and less mature before the crowding even begins ^[3]. Importantly, this initial challenge affects both lungs, not just the lung on the side of the hernia ^[1].

The Second Hit: Mechanical Compression

The “second hit” is the physical crowding caused by the herniated organs. As your baby grows, the hole in the diaphragm allows abdominal organs—like the stomach, intestines, and sometimes the liver—to move up into the chest cavity ^[4].

Because the chest space is restricted by these organs, the developing lungs do not have the physical room they need to expand and grow properly during the second half of pregnancy ^[5]. This mechanical compression acts as a second major roadblock to lung development, and it most severely affects the lung on the same side as the hernia (the ipsilateral lung) ^[1].

How This Affects Lung Function and Future Growth

Because of this two-step process, the lungs in babies with CDH are structurally different ^[2]. They have fewer air sacs for exchanging oxygen and carbon dioxide, and their blood vessels are also affected ^[6].

The blood vessels in the lungs often develop thicker walls, making it harder for blood to flow through them ^[6]. This can lead to pulmonary hypertension, which is high blood pressure specifically in the lungs ^[4]. Doctors will monitor this pressure using ultrasounds of the heart, called echocardiograms. Managing this high blood pressure is often one of the most critical parts of caring for a baby with CDH right after birth ^[7].

While this sounds intimidating, there is reason for hope. Your baby’s lungs are not finished growing when they are born. Human lungs continue to develop and grow new air sacs (alveoli) for several years after birth. Your care team will focus on stabilizing your baby to gently support their breathing, managing their pulmonary hypertension, and allowing their lungs the best chance to adapt, heal, and continue growing ^[8].