With DS1 I had done a load of active birth classes and learned about the physiology of birth. Basically if you follow this theory, in order to support the birth process, you want to be upright at much as possible as every contraction causes baby's head to put pressure on your cervix, helping it to thin and open. That will still happen if you're lying down, but it's most effective if you're upright because you're not working against gravity. For example see this ping pong ball demo - you can see that obviously it would still be possible to do this sideways, but upright is likely to be a bit more effective.
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Then when the baby is moving through the birth canal, if you're focused on how to most effectively push the baby down, you ideally want to be upright again (or, at least, on all fours/squatting leaning back/leaning forward over something/lying on left side with something between knees) in order to have your hips the most open they can possibly be, including getting the lowest bit of your spine (tailbone/coxxyx) out of the way.
The theory is that if you can use your position + gravity + moving your hips a lot then you'll get a more open, easy position for the baby to come out and therefore (in theory) you have less chance of needing an instrumental birth, episiotomy, etc, and labour might also be quicker and less likely to tire you out so much that you can't push effectively at the end and need assistance (instrumental/episiotomy again).
Obviously the caveat of this is that labour takes a long time (many hours, sometimes several days) and really bloody hurts!! So while we can have all this knowledge and understand that physiologically, it is likely to make it easier and go more smoothly and efficiently (and not tire you/baby out as much) - there is also the option of pain relief, with the main three options being G&A, opiate injection, and epidural.
In the absence of pain relief, it's possible (in theory) to get through the experience by sort of hunkering down and "being mammal" and sort of going into yourself, the endorphins then do their job, and there's a kind of helpful positive feedback loop of relaxation encouraging more of the contraction-inducing hormones, and then those hormones helping you to relax more, IME it doesn't make it painless at all, but it helps you get over each contraction "hump" as they are only about 60 seconds long.
Gas and air is totally compatible with the active type of birth, but doesn't really do a great deal, it kind of takes the edge off which might be enough. I found it helpful. But I wouldn't say that it really takes the pain away - it helped me feel like I was in control of something when I was starting to lose it, and gave me the push to get through the last bit which is extra tough.
Opiate injections are usually given if you're a while off actually giving birth but you're getting tired and frustrated, because they can let you rest and relax for a bit. It's temporary and they don't like to give this too close to birth because it can make the baby sleepy.
Epidural is basically the gold standard though, I'm told it totally numbs the pain but the issue is that it also immobilises you (so you can't do the active positioning stuff) and means that you need monitoring, which can be slightly stressful. Because you don't need the coping mechanisms to get through the contractions any more, I guess that the feedback loop isn't happening, although that doesn't mean you won't get the contraction-producing hormones, you still do - I think it's just that the whole thing is meant to work slightly less efficiently.
There are now "mobile" epidurals as people have mentioned which might mean you can still do the active bit, but they don't seem to be an option everywhere and I don't think I was ever offered one.
So in theory at least, it's meant to be a trade off between a painful/intense experience that is likely to be more straightforward and result in an easier recovery, vs an experience which is pain free but might work less effectively and might be more likely to result in longer labour which could mean more distress to baby or instrumental delivery which would be a more difficult recovery.
And, obviously also, it's not always as simple as that, because there are many things which can happen which makes the drug-free option less copable, or more painful, or not effective anyway. Babies can be awkwardly positioned, they can get stuck, they can be big, the environment might not be conducive to relaxation, you might have necessary interventions such as induction or there might be no conceivable reason, it's just different! There are no guarantees, so you could go all natural and have instrumental delivery anyway, or you could have an epidural and have a perfectly straightforward labour.
All other things being equal, it would make sense if it was just seen as a personal choice that people make with all their own personal factors e.g. pain tolerance, length/experience of previous labours, likelihood of complications, and it seems just as valid to me for one person to say "It doesn't make that much difference, I'd rather have the pain relief" vs "I'd like to see if I can optimise the process/have as hands-off an experience as possible". It also seems, because I quickly googled to see if there were stats about labour length, intervenstions etc related to epidural or not, that some of the info I've explained here is out of date and it's actually been found that epidural doesn't increase incidence of these things, so that might be worth investigating. I'll leave it in just because this was the basis that I made decisions on and it seemed to make sense to me.
Unfortunately there DOES seem to be a vocal minority who seem to see drug-free birth as some kind of pinnacle to aim for, for everyone when that doesn't really make sense. They often see intervention-free as some kind of goal as well which is even stupider because the majority of the time, you don't have any control over whether an intervention is needed, and when they are needed, you absolutely want them!! I do agree that policies/healthcare professionals should be trying to minimise use of intervention except when necessary, but it seems daft to try and paint this kind of thing as maternal choice, and even more daft to insist that there is a "right" vs "wrong" choice.
Ultimately, there are pros and cons to both options. For me, I opted for an epidural with DS2 when I remembered what it was really like after 10 years, and realised I didn't actually want to go through hours more pain if I didn't have to. However, it didn't work, and I ended up feeling more out of control and finding it more difficult. I opted for no epidural with DS3, because I just didn't want that to happen again, I honestly felt a bit daunted at the idea of being immobilised, the procedure to get the epidural in wasn't nice, and I was OK managing with coping techniques all the way through. But if the labour had been different, then it might have led to a different choice. He was actually breech up until 37 weeks and I had a c-section booked because I had no desire to do the breech birth vaginally, but he turned in the end.
Labour is hard however you do it and everyone who has been through it is strong IMO no matter how it went. I think the most empowering thing is understanding how all these tools - pain relief options, medical interventions, management techniques, environmental tweaks etc - can feed in and being able to feed into, or at the very least understand decisions about them when there's time.