Let me tackle the first part:  avoid giving birth on your back.

Some of the reasons vertical birth can be more beneficial than sitting or reclining:

• Gravity.  I think we all know about Newton’s Law, right?  It is pretty obvious that using the planet’s gravitational pull would be helpful in a normal birth scenario.  Upright positions ensure that the baby’s head stays evenly pressed against the cervix.  This pressure means more consistent dilation and speedier labor.  Also, the entrance of the baby’s head to the inlet of your pelvis is easiest when you are upright.
• It opens the sacrum and lifts the tailbone.  The sacrococcygeal joint is located between your sacrum and your coccyx.  It loosens during pregnancy so that your coccyx can tilt back out of the way as your baby is born.  When you lean forward on hands and knees or squat, this tilt happens.  What do you think happens when you are sitting on your tailbone?  Exactly.  The opposite:  it tilts in a bit.
• Optimal relaxation of the perineum.  The most common hospital birth position is semi-reclining with the woman’s legs pulled way back toward her ears.  I’ve assisted in countless births in the position.  Not only does this tilt the birth canal toward the ceiling (see point one about gravity) it also stretches the perineal muscles tight.  When the muscles are stretched externally, they are more likely to tear.
• Strong oxygen supply to the baby.  You’ve been told already not to sleep on your back.  Why?  The weight of your heavy uterus presses on some major abdominal blood vessels.  This pressure can cause fetal distress by hindering blood circulation.  When you’re already working hard to push out a baby, adding pressure to blood vessels does not benefit you or your baby.
• Less pain.  Ah–got your attention!  When you avoid laboring on your back, there is no direct pressure on the pelvic nerves that enter the pelvis through the sacrum.  Putting weight on your sacrum can compress these nerves causing you to experience unnecessary pain.
• Less work for your uterus.  When the uterus contracts, it tilts forward.  If you are upright or leaning forward, you make it easy for your uterus to assume this position.  Reclining, your uterus will have to heave forward with each contraction causing it to expend extra energy.

The woman to the above is using a squat bar at Greenville Memorial.  Doesn’t she look powerful?

Hmmm, so are there disadvantages?  Yes.  It is not the most convenient position for your care provider.  It is unusual (for some) and it throws a kink in some routines of creating a sterile field, keeping the laboring woman still for pushing, and monitoring fetal heartbeat.  I’ve heard all sorts of reasons given by OBs as to why their patient could not birth vertically.

If lying down is your preference for birth and what feels most comfortable to you, then of course, do it.  But what if you want to go vertical?  How can you make that happen at the hospital?  First, speak of your intentions to every doctor/midwife in your practice.  Second, put it in your birth plan.  Third, order the hospital birth bar.  Fourth, practice a few vertical positions to see which feels best to you and to get your body comfortable with these positions.  If you plan to squat, you will probably want to be supported.  You can be support on two sides by your doula and partner, you can have your partner or doula behind you on the bed, or you can use the birth bar to support your weight.  If you plan to birth on hands and knees, you can raise the bed so you can drape over it with your arms; taking pressure off your wrists.  If you plan to stand, you will want your partner behind you supporting under your arms or you will want to lean against the bed on your arms.

While the research and cultural history are on your side, vertical birth in the hospital is not the norm.  Remember, though, no one can make you lie on your back.  This is your birth and your body.  Your care provider is the hired help.