Why don't babies which are head-downwards for months have all the blood rushing to their heads?

[Wigeon]

Can someone scientific / medical enlighten me? Unborn babies spend weeks and weeks head down, with no apparent ill effects. If I stood on my head for weeks, I would feel terrible and get very red in the face. I'm sure there's a perfectly sensible medical / scientific reason why babies don't - please tell me what it is! It's been bothering me for a while .

I believe it's something to do with the fact that as they are suspended in water gravity has little part to play. This is not a medical opinion, simply my surmisation

Think of doing a handstand under water - no blood rush there huh?!

They do come out looking a bit red looking though don't they?

I have no idea why it is the case btw.

Always wondered this - good q!

Mine come out looking blueish.....

I believe it's to do with the fluid.

It does seem very odd to my mind though, I try to keep reminding myself not to refer to the baby as being upside down in case it hears me and decides it's better off breech!

Maybe babies have very low blood pressure?

Did occur to me that there was something which physics could explain about the baby floating in water. . GCSE physics didn't cover this!

I do did get a headache from doing a handstand in the swimming pool, but then I thought it might be to do with the pressure of the water or something ...

I should think the red-looking at birth is due to being sqeeezed through a teeny tiny gap .

C'mon, scientists, let us know!

love it! always wondering the same!

wikianswers:
You've asked why the fetus doesn't experience blood "rushing to its head" because of the upside-down position. First, the movement downward is slow, over days to weeks, so the baby adjusts to the "head-down" bloodflow, much like astronaunts become acclimated to weightlessness over time. Second, a normal fetal and neonate (just after birth) and the infant's heart rate is much higher than a "normal" for an adult. While adults have a normal heart rate of about 80 (give or take 10 beats), a fetal to infant's heart rate is normally 140 to 160. This keeps the fetus well-perfused (i.e. an adequate amount of circulating blood) to the brain and all extremeties and vital organs, regardless of the position within the womb.

also:

"The amniotic fluid that surrounds the baby acts as a cushion so that the pressure of gravity is not pulling on the baby as it does the mum."

yes.... I think the double heart rate and water are to thank it seems?

I don't think the amniotic fluid cushions against gravity theory 'holds any water', sorry!

Imagine this you have a sealed container with some marbles and you drop it into a pool of water. What happens to the marbles? They sit at the bottom of the container - the water doesn't cushion them against gravity. Gravity is just the same inside the container.

Ah - the first wikianswer seems sensible in terms of heart rate. But I don't get the point about the movement downwards being slow - the baby doesn't start off upright (breech) and then gradually rotate round over weeks, spending days or weeks being transverse for example - it might well just flip round to head-down. So it isn't like an astronaut. I think...

On the fluid-cushions-aganist-gravity thing - I see the
point, but surely water does provide some buoyancy (rather than protection against gravity) - picture a cork in the sealed water-filled container, which would just fall down if you dropped it to the ground out of water - does this have any affect on the baby-not-getting-a-head-rush question?

I think there's a difference between overall buoyancy and the effects of gravity on things inside a buoyant object. The baby could be floating in the amniotic fluid but its own body fluids will still be subject to gravity.

But the water thing is not simply about gravity is it? Surely the mass issue has an effect too? Otherwise, why do I float?

Obviously, I know absolutely nothing - I did get a D in GCSE physics after all!

Um, what do you mean by "the mass issue"?

Isn't floating about buoyancy, not gravity, and whether the object is heavier or lighter than water (marble = heavier, cork = lighter). And it can't just be about weight, because as you say people float in water but marbles sink. Er. Gravity just stops the object floating off into space and keeps it in the water to start with. Maybe.

Oh, right, I see. If an object is heavier than the water it displaces, it will sink. An object floats when the mass of the water it displaces equals its own mass.

But strictly speaking buoyancy isn't really about mass, it's more about density - ie, the amount of mass per unit volume. A marble is considerably more dense than cork. If an object is less dense than water then it will float. If not, it will sink. So a glass marble is more dense than water so it will sink whereas a piece of cork is less dense than water (due to the air trapped in its pores) so it floats.

Ah yes, that's it - density.

But more importantly - how does this all relate to an unborn baby in a womb not getting head-rush?!

I think unborn babies do get a head-rush from the blood pooling in their brain, albeit tempered somewhat by their fast heart-rate. But it's not like they're able to say "Oi, mum, I'm getting a headache!" is it?

Himalaya- the buoyancy of water does reduce the effects of gravity somewhat

Perhaps that's what I meant - density rather than mass. I told you I failed!

Schmoo - how is that then?

Gravity is the force between two heavy objects, it is a function of mass and distance. The earth is big, we are close to the surface, the force is considerable (but not that strong) the moon is smaller, it's gravity is less etc... Water doesn't come into it.

When you are lying in bed your bed is holding you up, when you are floating in water the water is holding you up. Gravity is the same in both cases.

When a person is floating in water the gravity felt by their blood and Internal organs (like the marbles in the box in my example) is the same as when they are on land. If they go deep underwater they are also subject to water pressure, which does effect internal organs but doesn't turn off gravity.

I have been wondering about this for as my baby is head down and has been since at least 32 weeks (I'm now 34+3). You would not hold a newborn upside down so how come it doesn't affect it.
I have a physics A-level (grade C in 2000) but sadly the subjects studied won't be able to help answer the question.
The baby will be a very similar density to the ammniotic fluid as humans are mainly water, gravity would act equally. I did wonder if it was to do with the babys balance? As we learn balance maybe our cardiovascular systems learn which way up we are suppossed to be? Eg there is a lot of pressure in the jugular veins in the neck as usually they are working against gravity but maybe in a baby these mechanisms are not so well developed?

yes himalaya- in that the water is holding you up is what I meant sorry- not that it is somehow negated!

I love threads like this! But I have to confess to feeling slightly smug as, while I understand why so many people get confused over the whole weight/density/buoyancy stuff, I was fortunate enough to study engineering for my degree so I can see the red herrings that some of you have fallen into .
Shmoo's Wikianswers post makes total sense. In the first and second trimesters babies spend lots of time upside down, upright and flipping between the two. If they settle in a breech position for a few weeks later on and then suddenly flip to head down, it's not the shock to the system that it would be for me having spent 30 years "upright"most of the time and then suddenly standing on my head for a while. My body's just not geared up to cope with it anymore than it's geared up not to overheat when immersed in a 37degree environment, but baby's is so he/she's fine.
Feel free to ping any more questions my way, although I can't promise to be able to answer them. Should we have posted this to the nuclear physicist professor who was on earlier in the week?

Ah ha! A scientist!

So, it's the fast heart rate keeping the baby's blood pumping round (not pooling in its head), plus the fact that it's been used to being upside down for some of the first two thirds of the pregnancy. But the "amniotic fluid cushions against gravity" is a complete red herring? Right?

But given a newborn baby's heart beat is also fast, and it has also been used to being upside down for the 1st and 2nd trimesters, presumably it would be a bad idea to dangle it upside down for hours on end (as saldoozer* says)? There must be something about being in a womb which is different from being on the outside.

Help! I feel no closer to discovering the answer to this important question! .

"amniotic fluid cushions against gravity" is a red herring - correct.

I'm not a medical professional so I don't know whether or not holding a baby upside down for long periods would cause any damage but I certainly wouldn't recommend it. I know shaking is definitely very bad because the brain is not properly cushioned inside the cranium when babies are very young but as for their orientation, I don't honestly know if it would hurt them.

I'm guessing that there probably aren't many clinical trials into the effects of hanging newborn babies upside down for long periods due to the small number of volunteers for a research project like this!

Much as I hate to say it, I think I'd have to pass on my midwife's seemingly universal but very irritating advice of "better to be safe than sorry" and refrain from hanging your baby up by its ankles.

HTH (but I doubt it!)