Why is LOA the best position for the baby to be in for labour?

[miranda2]

my dh insists I ask mumsnet this one!
I saw the midwife the other day and she said baby was left occipant anterior (spelling?), which was the best position for labour. I know I've read this in lots of mags. So i was v.chuffed and told dh. We were both pleased it wasn;t back to back (though there's time yet..), but then he looked puzzled for a minute and said 'so what is asymmetrical so that left is better than right?'. And neither of us could think of a plausible explanation! Is the pelvis and/or baby not symetrical? Or is actually left or right not an issue?
No reason for asking really, just interest!

[starlover]

hmm, my book says that left occiput anterior is the best position for labour, as you already know.
It then says that it can lie to the right, but it is not as common...

maybe there is just something that makes babies lie to the left?

Either way, it is the occiput anterior bit that is important, rather than the left/right

[CarolinaMoon]

i think (from what i've read, am not health pro or anything) that it is to do with the way your muscles encourage the baby to rotate down the birth canal. i even read somewhere that a ROA baby would have to rotate through an OP position to get to LOA before descending, but seems a bit far-fetched tbh. I found that stuff by googling when i was pg - there are various sites where MWs discuss their experiences and this is the type of thing that comes up.

anyway, no doubt people who actually know about this will answer your q...

[mears]

The baby's head fits into the bony shape of the pelvis better that way. It does not matter if it is the left or right. Once the baby's head has gone down through the pelvis, it reaches the pelvic floor and rotates so the face is facing downwards as it comes out. The head then glides out under the pubic arch (front part of pelvis), the neck extends and the face appears and the head is born. The baby's head then turns to face mother's thigh and the body is born with the next contraction. If women drive a lot, or sit a lot, the baby fits better into the back of the pelvis which is the OP position which makes the rotation for the baby a longer way to go. They can come out face up though (stargazer). Just takes longer because a wider part of the head is being delivered that way. An OA baby is able to flex it's neck so that smallest part of the head emerges first. Fascinating isn't it

[orangina]

Sorry, don't want to hi-jack thread, but have was wondering, I'm 37+ weeks pg and baby is not yet engaged (I think?!), but is head down and seems to swivel from being LOA to ROA and back again... Any idea if this will settle down? Does this matter? (Glad to hear that ROA or LOA are both good positions to be in, perhaps I shouldn't worry either way!). Thanks