The Mysterious Baby Timer

To cook a bun in the oven, set your timer according to the recipe and remove it from the heated chamber when the bell sounds. To carry this metaphor a little farther, what is the corresponding timer inside a developing fetus that alerts the mother when it’s done?

The mechanism, as we so far understand it, is proving very unexpected.

Researchers recently discovered that two specific proteins in a human fetus’ lungs activate genes to increase the production of a surfactant as well as a platelet-activating factor. These two compounds are then secreted from the fetus into the surrounding amniotic fluid where they trigger an inflammatory response in the mother’s uterus that initiates labor.

Say what?

In a nutshell, substances produced in the lungs of a full-term fetus provoke a reaction in the mother’s uterus that induces labor.

While it’s been known for some time that pulmonary surfactant (a substance that helps prepare the fetal lungs for breathing air) is produced as a fetus approaches full term, it was not previously suspected of initiating the labor process.

Most in the scientific community who’ve read the study have suggested that the discovery of a connection between substances secreted by a fetus’ lungs and the initiation of labor may eventually offer new avenues for preventing premature births.

And while this is clearly an important goal, the finding also raises bigger picture quandaries that I hope will also receive further study.

For example:

1) Why is it not the mother’s body that decides when the baby is ready for the world, but the baby itself? How did this phenomenon come to be? And does it in some way reflect the widely shared feeling among expectant mothers of having their bodies “taken over”?

2) Why the lungs?

Are the lungs in charge of labor timing because they’re they last organ to be prepared for terrestrial life? Or does their critical role harken back to a time when our predecessors existed entirely in water? And what might this suggest?

3) And perhaps the most interesting question — Why is the mechanism for initiating labor an inflammatory response?

Such a response is normally triggered by a pathogen, injury, or antigen — and works to prevent either actual harm or the imagined harm that launches a full-blown allergic reaction.

So does the body of an expectant mother, in the end, view its fetus as a pathogen or allergen?

And if so, how and why would such an arrangement have evolved?

And what might it tell us about the primordial, evolutionary relationship of mother and fetus? Was it as wholesome and mutually beneficial as we believe it to be? Or was it more conflicted for some reason?

As usual, many more questions than answers.

But this is just the tip of the iceberg.

The plot thickens with the recent discovery of more stowaway viruses built into our DNA. Known as endogenic retroviruses, they essentially act like genes and take a variety of actions, some of which have been shown to influence reproduction.

For example, one endogenic retrovirus becomes active inside early-stage human embryos, assisting in their formation and protecting them from other viruses.

While another activates inside the placenta where its presence works to suppress the mother’s immune response during pregnancy.


That’s shaping up to be one complicated little bun!

(more on other stowaway viruses that manipulate embryos in a future post)


Photo: Lennart Nilsson, originally published in Life Magazine 1965. Human fetus at 10 weeks. The eyelids are semi-shut. They will close completely in a few days.

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