Fantastic voyage from the womb
The amazing changes in a new born baby’s circulation
It’s three in the morning, and my pager jolts me awake from a brief 15-minute slumber. It blinks with the words “Code brown—delivery room 4”. My feet hit the cold hard linoleum and I slip on my shoes. Entering room 4, the bright lights constrict my pupils. I meet up with the drama, excitement and fear of the expectant father who grips his wife’s hand as she is writhing in pain. The obstetrician sitting at the foot of the bed encourages the mother to push again. Not looking up, he alerts me that when the mother’s membranes ruptured (water broke) the fluid had a greenish hue. This signifies that the baby had had its first bowel movements in the womb during the stress of the delivery. These will evacuate its bowel contents—a sticky, tar-like substance called meconium—into the amniotic fluid. If a baby aspirates this into its lungs it will compromise its breathing, and the transition from the womb to the outside world would be difficult.
I grab a sterile towel, and with expectant hands I brace myself to accept the baby. As a pediatrician, I have attended countless deliveries; my eyes still well up a bit with tears at the astonishing wonder of birth. It never gets old; I am in awe of God’s design.
The transition of a baby from the warm comfort of the womb into this immense, noisy world is nothing short of phenomenal. Adult circulation, which begins when the baby takes its first breath, is very different from fetal circulation. In the womb, the baby, attached to the mother through the placenta, resides in a fluid environment.
The placenta is the life support of the baby. The kidneys and lungs (as well as digestive and immune systems) do not function at full throttle when the baby is in the womb. The placenta takes on the lion’s share of work for these organs, awaiting their maturation outside the womb. It provides nutrients and oxygen for the growing baby, and whisks away waste products.
Much could be said about the complicated physiological relationship of the mother and the baby. For instance, how the placenta forms a barrier of sorts between the chemicals in the baby’s and mother’s blood, while allowing oxygen and carbon dioxide to cross. And how the early cells, present after fertilization, implant to form the placenta, and so much more. Each in itself is truly a remarkable piece of engineering. But this article—definitely not exhaustive—will focus on how the baby transitions from fetal to adult circulation.
As humans, we like to build things. But as any architect or engineer can tell you, just because you can imagine it in your mind or even sketch it on paper doesn’t mean you can actually build something that will work. When it comes to building a house or a computer, the process involves much more than just putting a bunch of materials together in the right location. It also requires a correct sequence, specific timing, a controlled environment, additional parts used for temporary scaffolding or temporary function, directed energy, and an army of workers that all understand how to read and follow the blueprints for the design they are bringing to life. No one would deny that such complicated creations originate from a masterful designer. As we will see, the nature of fetal circulation resonates with extraordinary design.
The developing baby
Let’s begin our journey through the circulation of the developing baby—see fig. 1 as a guide. The nutrient- and oxygen-rich blood leaves the placenta via the umbilical vein. This vein carries blood towards the baby’s liver. A small amount of blood is sent to nourish the liver but the majority of the blood bypasses it through a vessel called the ductus venosus (DV)—one of the main temporary ‘bypass shunts’ God has designed at key locations. The blood of the DV flows into a large vein called the inferior vena cava (IVC). This is the vessel that brings deoxygenated blood from the lower extremities to the heart. The IVC enters the right one of the heart’s two upper chambers (‘entrance foyers’, if you like), the right atrium (RA). Another large vein, the superior vena cava (SVC), enters the RA, ferrying blood from the head and upper extremities.
Some of the baby’s blood is shunted from the right atrium across to the other side, to the left atrium (LA), by way of a temporary opening called the foramen ovale (FO). This is a hole in the wall dividing the two upper chambers of the heart. (Most people have heard of ‘hole in the heart’, the condition where this opening fails to close after birth as it should.) Oxygenated and deoxygenated blood mixes in the right and left atria.
Most of the blood remaining in the RA moves on to the right ventricle (or ‘pumping chamber’), just as happens in the adult. From there it is pumped towards the lungs via the pulmonary trunk, which divides into the right and left pulmonary arteries. In the unborn baby, the walls of the alveoli (tiny sacs in our lungs) are pressed together—collapsed, not expanded as they need to be for gas exchange in respiration once the baby is breathing air.
Like the liver, the lungs are only minimally functional in this aqueous environment. They receive a small amount of blood for sustenance, but most has to ‘bypass’ the lungs, so it is shunted from the pulmonary trunk directly to the aorta—the large artery, the outflow of the left ventricle (LV) that supplies the body with oxygenated blood. This bypass is via another crucial (but also temporary) shunt, called the ductus arteriosus (DA).
The rest of the blood returns from the lungs by way of the pulmonary veins to the LA, then to the LV, which pumps it to the rest of the body, leaving the heart through the aorta. On the final passage, in the terminal aorta, a portion of the blood is diverted to the umbilical arteries, which return it to the placenta to pick up more oxygen and unload its carbon dioxide and other waste products. The other portion continues to the pelvis and lower extremities.
The newborn baby
Returning to our analogy of building a house, this new, designed human form must be able to operate on its own in a way quite unlike in the womb. It must have its own electrical, heating and cooling, waste management, maintenance and repair, security, communication, and control systems in place and working properly.
Anticipating the arrival of my newest patient, the baby’s head emerges after a great push by the mother. The obstetrician quickly suctions the mouth and nose of the baby with a hand-held bulb syringe as it presents. The baby’s eyes blink quickly, temporarily blinded by the lights as it emerges from its dark warm environment. The baby is delivered.
The obstetrician clamps and cuts the umbilical cord. This is one of the events that signals the astonishing change from fetal circulation to adult circulation. The placental flow stops instantly with the clamping of the cord. The umbilical arteries and vein are now disconnected. Air enters the lungs to expand the sacs, and breathing begins. All this causes blood flow to the lungs to increase as the vascular resistance in the lungs decreases. Pressure in the LA increases while the pressure in the RA decreases. This pressure change between the two atria causes the flaps of muscle around the FO, the hole that served as a shunt between them, to fold in so it functionally closes.
The shunts of the fetal circulation, the DV, DA and FO, begin to shut down functionally with that first breath. The inside of each of the two vessels is mostly obliterated by fibrous tissue growth in the first months of life, and they become ligamentous structures. The lungs rapidly become fully functional, and the placenta has shut down for business. The baby begins a life independent of the confines of the life-sustaining maternal incubator.
I am handed the precious cargo, and promptly walk over to the warmer. I begin to suction deeply into the lungs of the baby to remove any possible meconium it may have aspirated. The baby gasps, coughs and begins to cry. Vigorously, I dry her off. Drying stimulates a baby to cry strongly. Her ashen skin colour begins to change to a natural healthy skin tone. Behold, an astoundingly engineered feat has just taken place.