Sorry this is a bit fragmented, but I am pregnant & very nauseous & trying to work all at the same time.
If you're gonna be birthing in the tub, you're not supposed to put the oils in there as they could get in the babies eyes.
When I was in labour I sniffed clary sage as I have always found it helpful for period pains. I also had a major craving for some jasmine sambac but couldn't find my bottle. I gave birth accidentally unassisted at home which all the aromatherapy people I have spoken to attribute to the clary sage altho' I'm not so sure. My first labour was 3.5 hrs so I think it was just me. I would have been prepared & made myself a blend but dd was 1 week early & I didn't think I was in proper labour until she was born!
Most of the books you get on aromatherapy are total BS, but maybe get one out of the library & see if you can find a blend that relaxes you without worrying about any supposed therapeutic use.
Some oils I would suggest off the top of my head are :
frankincense - good for meditation & helps deepen breathing.
myrrh - ditto
Actually I think some of the ancient meditation oils would really help for labour as it is the ancient, primordial part of the brain you need to tap into....
rose - feminine, relaxing.
jasmine - ditto
lavender - clean smelling, light, gentle, good muscle relaxant.
neroli - good for calming nerves.
chamomile - ditto
You could make a blend of any 3 of these that appeal to you & put it in a burner. You could use hot compresses of clary sage for pain relief if the contractions get really strong.
Depending on how long you are in labour & what effect you need, you may like to add some citrus oil, like grapefruit, to wake you up a bit.
You can also get hydrosols which you can spritz around the room.
My fave supplier in the US is
www.naturesgift.com She could have some good suggestions or a premadeup blend all ready to go which would save you heaps of dough.
Good luck & remember, the key is to get a blend you like & also be open to the fact, you could change your mind in labour or get a strong craving for an oil you need.