#66 Do Babies Breathe in the Womb?

For the baby in the womb, breathing has two meanings. The baby’s exchange of oxygen for carbon dioxide is not accomplished by inhaling and exhaling amniotic fluid. The placenta sends oxygenated blood to the baby by the umbilical vein and removes carbon dioxide from the baby as the umbilical arteries return to the placenta. In the uterus, the baby’s lungs do not work to exchange carbon dioxide for oxygen.

The baby, in the process of moving amniotic fluid in and out of its lungs helps the baby prepare for the transition of moving air in and out of the lungs after birth. By 10 or 11 weeks of pregnancy, the baby in the womb begins primitive inhalation of amniotic fluid. This action is more like a combination of swallowing and inhaling, but it helps the baby’s lungs start to develop. By 20 weeks, the baby gets more serious about breathing and between 24 to 28 weeks breathing practice increases to about 10 or 20 percent of the time. By week 30, the “breathing” increases to 30 or 40 percent of the time. By 32 weeks, the baby’s lungs are fully developed and the baby can survive outside of the womb.

Fetal breathing movement is important in lung development. Additionally, moving amniotic fluid in and out of the lungs helps develop the alveoli, the small sacs in the lungs which actually exchange oxygen for carbon dioxide. For the lungs to work well, the baby needs a surfactant, a chemical to reduce the surface tension between the alveoli and the fluid surrounding the alveoli.  Surfactant production begins at about 26 weeks of gestation but isn’t complete until about 36 or 37 weeks. I know from personal experience if a baby is born spontaneously at 36 weeks, they seem to have no trouble breathing. On the other hand, if the baby is delivered electively (by the choice of the doctor or mother) 36 or 37 weeks they may have very significant breathing problems.

In order to accomplish air exchange, the alveoli must be able to open and close. The walls of the alveoli are only two cells thick. Without low surface tension, these cells can’t reopen once they are emptied. This means the alveoli require low surface tension to re-open. Difficulty with the air sacs opening is the main problem associated with premature delivery.

I attribute this difference  between spontaneous birth at 36 weeks and elective C-sections at 36 weeks to the baby’s making the decision to be born when it is ready to be born. There is something to say about getting ready for delivery and babies most often seem to know when the time is right. They have been deciding when to be born for millions of years and it is hubris to think we actually can know better than the baby about when to be born.

When you go into labor and your body prepares for delivery, your baby stops exchanging amniotic fluid. So your baby’s lungs have little or no fluid in them at the time of birth. Shortly, within 10 seconds after delivery, your baby will respond to the drastic change in its environment by taking its first breath of air. This miracle, during which your baby changes its oxygen source from placenta to lungs and room air happens thousands of times each day. It is the most intricate and meaningful event of a lifetime. The lungs of your child will keep fine-tuning and growing until your child is eight years old.