Picture: MaxPixel
Picture: MaxPixel

This is what happens to a baby’s body during birth

By Ian Wright Time of article published Jul 7, 2019

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Pregnancy, labour and delivery are incredibly physically demanding for women. But birth is no walk in the park for the baby either.

Sudden increase in oxygen

Before the baby is born, blood goes through the placenta to get rid of waste and to pick up oxygen and nutrients that come from the mother. The developing baby manages on relatively low oxygen levels while in the uterus.

After birth the child is exposed to suddenly higher (potentially dangerous) oxygen levels. This shift requires different ways to protect the newborn – so the baby has systems ramped up to cope with this sudden flood of oxygen. Mild jaundice, a temporary yellowing of the skin resulting from a delay in liver enzymes kicking in, may be one such protective mechanism seen in many infants.

Physical changes plus shifts in biology and chemistry of the body’s systems are required to cope with the outside world.

Goodbye placenta

Before birth, most of the baby’s blood circulation passes through the placenta, but bypasses the lungs.

After delivery, the placental flow stops. Instead of going from the baby’s heart to the placenta, the blood from the heart needs to redirect through the newly expanded lungs.

New research helps us understand the relationship between baby’s first breaths and the expansion of lung blood flow.

Understanding these processes in the first few minutes guides us in knowing when exactly to clamp the umbilical cord, and to time any breathing help needed for sick or premature newborns.

It doesn’t always go to plan

The many changes a baby needs to be ready for delivery do not always have a chance to take place.

For example, if a baby is born prematurely then some or all of these adaptations may not have occurred.

Premature babies may have trouble opening up their lungs, or they may not close off the relevant bits of “plumbing” to redirect blood flow to the lungs. Or they may have difficulty exchanging oxygen and other gases in the lungs.

Other body systems such as skin, guts and the body’s chemistry systems may also be relatively unprepared.

Despite this, all but the most premature of babies benefit from the boost of labour if possible. The changes associated with the onset of labour, particularly inflammation, trigger the biological signals that tell a baby to get ready for being born.

Caesarian delivery

Surprisingly, even a small deviation from normal, full-term (around 40 weeks) timing of labour may have effects.

Babies born by caesarean section without labour do not transition to the outside world as smoothly as those where labour has commenced. They have a higher rate of admission to neonatal units for respiratory problems, even after adjusting for other risk factors. Every week earlier than delivery at 40 weeks roughly doubles the risk of neonatal unit admission for babies.

Current recommendations for birth timing are to balance the risks of delivery with these immaturity risks, and not deliver too early unless it is medically required.

Some of these effects can be altered by steroids. Steroids are made naturally by our bodies, including in babies. Also referred to as “the body’s stress hormones”, these are particularly important in making sure lung maturity happens at birth.

Sometimes steroids given to the mother can trick the baby into “preparing an escape plan” and getting lungs ready for delivery before term.

Independent of mild prematurity, researchers are looking closely to determine if there are any long term health and developmental effects of being born by caesarean section, without the process of labour and delivery.

Squashed head

But why do we have such a high-risk delivery system, one where the baby has to actually deform its skull to be born?

Humans are defined by our brains. In our species, the process of evolution has been a balancing act, where brain size and maturity have been weighed up (in terms of survival) against the risk of obstruction in labour.

Human babies are relatively immature compared with some of our close primate relatives, but we cannot safely achieve more brain growth before delivery. For us, this extra growth has to occur over the first year or so after birth.

In addition, because we walk upright, this has created a tilt in our pelvis which narrows the birth canal (the gap in the bones of the pelvis through which the baby has to pass).

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