I did a search on the archives here for the keywords “upside” and “down” but didn’t find an answer … maybe you Teeming Lurkers can help?
Every pregnancy book I can get my hands on points out that the child generally spends a lot of time in a position we would consider ‘upside down’, that is, head pointed down and butt pointed up.
Why doesn’t the blood rush to his/her head and be uncomfortable, as it does for us humans ex utero? Or does the pressure/fluidity of the amniotic sac/fluid equalize the pressure internally and externally enough that it’s not a concern?
IANADoc, but don’t forget that the amount of blood present in the baby is much less than that in an adult so there would be a smaller mass of fluid providing the presure.
No, I don’t think buoyancy is an issue here. I think that (1) the kid isn’t quite upside down (i.e., the fetal position curves the cervical spine so that the head is in a slightly more horizontal position; (2) the fetal position also holds the legs curled, so that there really isn’t that much distance involved; (3) the blood mass in a newborn is what – two pounds? Five? That’s not enough for gravity to hurt much.
If anyone actually knows, of course, I’ll defer – but that’s my speculation.
I remember reading that major changes occur to an infant’s circulatory system at the moment of birth; the chambers of the heart are connected in some way by holes that close up in the first few minutes (unless they don’t, which is how the baby-with-a-hole-in-the-heart thing happens).
the head down position is normal really only at the end of the pregnancy just before birth.
really though the babys head represents a much bigger proportion of body weight than in an adult. The head I think is fully half the mass of a baby which means that a much larger proportion of the blood in the body already is in the head. In an adult body there is much more volume outside the head than in it.
Not always near the end does the child change position … it usually happens anywhere between three and four months before birth up until just days before birth … mostly because there isn’t a lot of room in there to flip around after a while.
I’ve had a … large number of ultrasounds because of other minor considerations and becau$e they reali$ed that I wa$ an excellent candidate for $uch mutilple vi$it$ and in$urance covered all the$e ultra$ound$ … and after a “big movement” recently, the child has been and still is “upside down” (though not “dropped” for birth, which can happen between a six weeks to a day before labor begins) and his movements still indicate that he remains in that position (I can feel his butt up in my ribs, lovely).
I’ve actually got until mid August to go (Due first week of August but babies on my side tend to run two weeks late).
The part about the circulation kind of makes sense … after all, the placenta is pretty much handling most of the blood transfer right now, is it not? Even though the heart is beating and doing some of the work. And the kid isn’t actually breathing, either … just sucking fluid in and out of his lungs, so maybe that has something to do with it as well?
As for holes in the heart … that kind of sounds right but not … not sure … I think there are some changes (obviously as the heart takes over completely and the lungs start functioning with air instead of water) after birth, but some holes can be detected before they are born (not many, though) … but I do recall a lot of kids being born with ‘holes’ in their heart where things didn’t close up but then eventually did.
So, maybe it’s like the kid is scuba diving for several months? Do scuba divers and deep sea divers have a problem being “upside down” for a length of time (aside from vertigo)?
I posted a form of this question on my “mommies” group and got back this answer from a scuba diver:
So that leads me to think about being out in space, too, I guess as there is little gravity pressure there, the body just gets used to it … so maybe the kid just never “feels” strange? But then again, they aren’t really in space, they’re in a pressurized environment with reduced gravity (much like in the womb, as the amniotic fluid provides bouyancy) …
But then that doesn’t make sense because I guarantee if I whelp this kid and start carrying him around by his ankles, he’s not going to like it very much.
Right, now I’ve done it. After lurking for years, you got me to register because I have not one, not two, but THREE relevant points to make!
Point 1: the pressure exterted by a column of fluid is proportional to the height of the column and the density of the fluid. That means for a (say) five-foot tall adult the change in pressure is five times as large as for a 1 foot “tall” infant. But only in air, where the change in external pressure is negligable.
Point 2: When I SCUBA or am otherwise underwater, I don’t get nearly the “head rush” thing as out of the water. That’s 'cause the pressure of the water outside neatly counteracts the pressure of the blood inside. The only parts on which you’d feel a difference would be places where there is an air gap, which you should be “equalizing” anyways.
Point 3: My 10-month old daughter LOVES to be upside-down. She might even be willing to spend all the time upside-down if that didn’t make it hard to nurse! Nothing is more certain to induce giggles and grins than being swung by her thighs. YMMV. Merely holding her upside-down does not seem to induce much “red face”, but swinging from overhead (about 7 feet up) to between the legs produces some “red face”. I also note this makes her mother nervious.
The point about scuba is interesting. I love swimming under water. I regularly go down 20 feet in a free dive. The only effect orientation plays on me is the “torque” of my chestful of air around my center of mass. (Using that info alone I can tell my orientation with eyes closed. Yeah, I’ve swum in some fairly murky lakes.) Pressure differences are not discernible.
Sort of a continuation on the SCUBA front. I think the answer you are looking for can be found in a pilot / astronaut’s pressure suit. By the time the little one is big enough for up and down to have any meaning it is completely enclosed in natures little pressure suit. I’m pretty sure that the force of gravity is a pretty minor factor when compared to the force of the uterine muscle wall.
