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Author Topic: Why does the growth rate of a human fetus change during pregnancy?  (Read 5571 times)

DiscoverDave

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A recent news story told of a mother and baby who died during childbirth but who came back to life.  This story referenced an older story of a 23-week-old fetus who survived a premature birth.  This prompted me to learn the typical weight of a 23-week-old fetus (about 500 grams, 1.1 pounds). 

I found a site with average fetal growth data, and when I plotted the weight logarithmically, I found three distinct growth periods with different growth rates (shown below).  The crossover points occur at about 16 and 36 weeks.  Does anyone have any ideas why different periods of development would have the growth rates?


 

Offline Variola

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From memory-
The 1st trimester is dedicated to formation of the foetus, by the end of week 12 the foetus has a full set of internal organs, limbs, brain etc. It is where the 'blueprint' for the baby is laid down and where most genetic defects happen.
The 2nd trimester is dedicated to growth,particularly from 16 weeks onwards. The foetus growth is dedicated to further growing and developing internal organs, brain, bone density sexual organs, eyes etc. The foetus also starts moving, stretching and practising breathing techniques, and they start to open their eyes. By week 28 everything is formed and ready to go. Hence babies born after 28 weeks are much more viable than those born before.
The 3rd trimester is dedicated to growth and putting on weight, during the last 6 weeks the baby can put on up to half a pound a week! Which explains why women go from having a neat bump in the 2nd trimester to looking like a space hopper!!! :D Putting on weight and laying down fat reserves is crucial for how the baby will survive after birth, it is known that low birth weight babies, even at full term have health problems.

HTH Dave.
 

Offline Variola

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LOL!!! Ah yes but growth is constricted by room left in the uterus (thankfully) which is why twins or triplets tend to be smaller and be delivered sooner as the uterus becomes stretched to full capacity. And also why subsequent babies are bigger as the womb has already been stretched.

If evolution really worked we would evolve a small trapdoor to let them out...!!!!! :D
 

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