A better question is, "What position will be best for MY birth?".
A woman's position for pushing her baby out is best known at the time of birth. Sometimes a woman's pelvis will favor one position over another. Sometimes babies position will favor one position over others. Sometimes, babies size or mamas urge to push will favor one position over another.
The best thing a woman can do is know her options for birthing positions, and which ones have which benefits for what scenarios, and then listen to her bodies cues during labor and birth to know what position is best for HER birth.
So, what are the most common positions for labor and birth?
Hands down, the most common position for birth in a hospital setting is the LITHOTOMY position . This position is marked by a woman in a completely (or nearly completely) prone (flat on the back) position, legs flexed at the knee, and resting in stirrups. This is the position most used for pelvic exams as well.
This position is one of the worst routinely used positions for birth that there are. It compresses the pelvic outlet, making the passageway for baby to move through even smaller than usual (in fact, up to 30% smaller). It also causes the tailbone (coccyx) to act as an uphill path that baby has to navigate UPWARDS against to get out.
Additionally, this position restricts a woman from freely moving by 'pinning' her in a position with her legs up and out of the way. This increases mom's risks of cervical lips, posterior babies, asynclitic babies, muscle soreness, symphysis pubis dysfunction, and cesarean. This position also puts greater pressure on the perineum, which can lead to other unnecessary interventions or complications like tearing, episiotomy, forceps delivery, or vacuum extraction.
This position is most used in hospitals because it is easiest for the medical professional to see what is happening and allows them to have a more hands-on approach to the birthing process. It is also often used when a woman has no feeling or mobility of her legs because of a heavy epidural.
There are a few times when this is a good position for mom to birth in. One of the times is when mom has no urge to push and baby is showing some distress. When a mom is on her back, the Ferguson Reflex is stimulated more than in some other positions, which can help mom feel the overwhelming urge to push, allowing her to push in an emergent situation. It is also a good position when there is an actual need for the medical professional to be more hands-on, such as, shoulder dystocia or other complications.
This position is marked by mom being slightly elevated, around 45 degrees, from the surface she is birthing on. This is the second most common position for women in the hospital setting. Some call it simply a variation of lithotomy. The reason is because, although it gives mom greater power from the added benefit of some gravity, it has many of the same risks as the lithotomy position. It is reported to result in better FHT (fetal heart tones), better apgar scores, and less incidence of resuscitation than lithotomy though.
The semi-sit has been reported to result in the greatest incidence of anterior lips and posterior presentation.
So, when mom has no sensation from a heavy epidural, many argue this is a better position than lithotomy. Other's still, though, will argue that, it is better for baby to navigate an upward slope (coccyx) than to have the coccyx pressed into the babies space. I argue that it is better to have mom on her side in side lying if she has a heavy epidural and forgo either of these positions.
On the other hand, this position is one of the most assumed positions in a waterbirth. The pressure of the coccyx does not come into play in a waterbirth, though, as mom is in a gravity neutral environment in the water and her coccyx is, thus, not compressed. It can still encourage posterior presentations, but the water will often alleviate the back labor associated with it, allowing for a more easeful posterior birth. Also, in a water birth, the pelvic outlet is not compressed, as mom can float into any position necessary, or allow her legs to be as open, closed, or asynclitic as necessary.
Standing positions use gravity to the mother's advantage. Baby is allowed to drop into the pelvis more readily and allow full mobility, including mom having full control over how wide her legs are, how deep her 'press' is, and how strong her push is. This position is also great to allow the birth team to apply heat or cold, counterpressure, or acupressure to mom as needed.
This position is great for a posterior baby, a large baby, or a baby who is asynclitic. It allows for full mobility, meaning mom can rock, dance, and tuck her baby down through her hip, upper body, and lower body movements. It also opens her pelvis optimally, giving baby a straight path to exit from. Many women end up giving themselves clitoral/anterior counter pressure during crowning, which allows them a degree of control as well.
A variation of the standing position is the asynclitic stand, aka the Captain Morgan, which is good for when a baby is asynclitic or has a hand up by their face/head.
The standing position is difficult for mom to see baby or touch baby during 2nd stage, and can sometimes be a detriment, such as when mom is very weak/tired, if she has a very precipitous birth and wants/needs a more controlled/slow birth, or if mom is intent upon catching her own baby.
This position allows for mom to completely relax between birthing waves and is also a gravity positive position. It is marked by mom sitting on a toilet, birthing stool, or partner's thighs, with the mother's knees bend at a 90 degree angle and planted firmly on the floor.
It opens the pelvis and allows for mom to open her knees as wide as she is comfortable with, adjusting her hips and pelvis as she feels is necessary, and is a great position for mom to catch her own baby.
This position is great for a mom who needs complete relaxation, such as in the event of a long labor or pushing stage. It allows for mom to be actively involved by providing her own perineal counterpressure and the ability for her to see baby's descent with a mirror. Partners can also provide counter pressure or hip squeezes easily enough in this position.
If mom is sitting on something that puts pressure on her sacrum and coccyx, such as a chair or birthing ball, though, it can put unnecessary pressure on babies presenting part and mom's anatomy, which can add stress to baby or pain to mom.
Squatting allows the pelvic outlet to increase, an average, of 10%. It is also a great position to close the top of the pelvis, effectively engaging baby into the birth canal. It is a great position for when babies are trying to find the optimal position for birth, such as when a baby is still moving around for the best route, but mom is feeling the urge to push.
This can be achieved through the assistance of a partner/companion, a birthing ball at mom's back, a ribozo to pull against, a squat bar, or any other surface to 'hang' from.
This position can be overwhelming, though, as it increases the pressure at the fundus as well as the pressure felt in the pelvis, but is a great position for large babies, babies who are asynclitic, and babies who need help descending.
The drawbacks are that mom has to rely on the strength of her legs to hold her up, unless she is settled back against something or someone while in the squat, and it can be difficult or painful for extended periods of time and/or for moms experiencing moderate to severe edema in the ankles and feet.
HANDS AND KNEES
This position is, in essence, exactly what it sounds like. Mom can be on her hands and knees (like a crawl) on her elbows and knees (with her buttocks in the air), on her forearms and knees (with her buttocks in the air), or hanging over a birthing ball, stool, partner's lap, or other low surface, on her knees.
This gravity neutral position is excellent for posterior babies, women experiencing back ache or pain, large babies, breech babies, and babies where shoulder dystocia is suspected. This position takes pressure off of the umbilical cord, decreasing the incidence of late 2nd stage fetal distress and decreases pressure on the perineum, resulting in a decreased incidence of tearing. It allows baby the most room to navigate the pelvis as it allows the uterus to hang, giving baby added space to twist and turn its head into the best position to exit, and the pelvis is given more room from mom's ability to rock, sway, tilt, and raise/lower her hips/posterior.
When mom chooses to have her buttocks in the air, it can mean longer to birth baby, as baby has to make an upward journey, but can be helpful when mom wants more control in pushing, the perineum needs more time to stretch, or when baby is persistently posterior. This is especially beneficial for the latter as this allows mom to widen her hips as much as possible, drop baby out of the pelvic outlet momentarily, opening the pelvis to it's maximum capacity, and giving baby time and space to rotate to an anterior position.
The kneeling position is done with mom on her knees, with her buttocks raised off of her calves.
The frog squat is the same position, but with moms buttocks sitting on her calves. Many women find that, in the frog squat, they will lean forward with their hands on the floor as well.
Some women even choose the asynclitic kneel, which is achieved by assuming the same position as one would when proposing for marriage. It can be done with hands on the floor or upright (like the standing asynclitic, only on one knee).
Kneeling includes many of the benefits of the squat and hands and knees, without as much gravity as the squat and not as gravity neutral as all fours. It is great for a mom who is fatigued but not ready to try a gravity neutral position such as side-lying. It reduces the incidence of tearing, is a great position for mom to catch her baby in, and, depending on how she assumes the position, can promote relaxation and rest between birthing waves.
The asynclitic kneel is great for an asynclitic baby or a baby in transverse arrest, as well as for posterior babies to give them ample space to rotate. Times when kneeling/frog squat might not be a good position is when baby is showing some signs of distress or when mom needs more rest/control, such as with a gravity neutral position.
Side-lying is a gravity neutral position that allows mom control of the pushing stage. When using the side lying position, mom is resting on one side, almost in the fetal position. The variation would be that her top leg would be either raised, or opened, with that foot resting downward (on the bed or other surface mom is lying on), so that baby can come down and out.
This position is relaxation specific, a great position for mom to completely relax between birthing waves and to reduce all unnecessary muscular effort. This is an optimal position for mom's who are fatigued or exhausted.
This gravity neutral position is also great for baby. It removes pressure from the uterus, and, in turn, reduces the chances of compression of the umbilical cord. This position has a low incidence of fetal distress because of this. It also allows for a more controlled crowning and for mom to catch her own baby with ease.
Drawbacks are that large babies sometimes need the extra space that a more 'open' position (such as squatting or kneeling) allows for, as it is gravity neutral, it can lengthen the 2nd stage, and some moms report feeling 'confused' at the 2nd stage because the urge to push can be less overwhelming, resulting in more of mom-controlled versus womb-controlled pushing.
No one can tell what position will be best for their birth until they are in birth. The best thing is to know the benefits and contraindications for each position, try them out during pregnancy to see which feel comfortable to mom physically and emotionally, and be ready to listen to her bodies cues at the right time.