Dr. Greene's Answer
“Why” questions are often the most interesting and the most rewarding. They are also among the most difficult to answer.
Your observations are correct — premature children who have been subjected to stress tend to have better survival and less lung disease, compared to those premature babies who are born without a preceding stressful period. Your observation that the administration of steroids to mothers in pre-term labor tends to speed fetal lung maturity is also correct. But, why should these things be?
When a child is born, the lungs change from fluid-filled sacs to air-breathing organs. This transition is an important part of birth. During labor, mechanical forces help to squeeze out fluid from the lungs. Steroid hormones secreted by the mother during labor also help ready the baby for the transitions of the first day of life. The body normally secretes corticosteroids in response to stressful situations — including labor. These hormones affect every cell of the body, preparing them to meet the stressful situation.
A child who is born before the normal gestational age has not yet finished in-utero development. If the delivery is abrupt, a partially developed baby is born. If, on the other hand, the baby has been subjected to a period of chronic stress lasting for at least several days before the birth takes place, the baby “realizes” that she may be delivered too soon. The most vital steps of maturation (notably regarding the lungs) are rapidly accelerated. The mechanism for this is the release of stress hormones. This situation can be mimicked when a delivery is imminent by treating the mother with a steroid such as betamethasone. This has been proven to accelerate lung maturation, including the production of surfactant (a “soapy” film that coats the inside of the lung, reduces surface tension, and makes breathing easier). The design of our bodies is truly fabulous. When the normal situation (for example normal gestational period) doesn’t pertain, self-correcting, healing mechanisms are in place to try to get us back on track.
One way to think about steroids, or stress hormones (which have many effects throughout the body), are as agents that tend to mature us. In premature infants, the stress tends to make them ready to face the world a little sooner. In children who are chronically stressed or treated with steroids, a common side effect is premature closure of the growth plates of their bones — they reach the end of their growth more quickly. Adults who are stressed or who are treated with steroid hormones tend to reach the next level of maturity, (including osteoporosis, cataracts, diabetes, heart disease, and death) more quickly.
Thus some degree of stress, of challenge, is necessary to keep us moving forward and growing throughout our lives, but as you can see, excess stress is destructive. Brief periods of great stress help to move us through crises, but chronic excess stress is unhealthy. Live in a zone of moderate challenge.