The process of giving birth vaginally is one which is common to all cultures. However, the best position in which to accomplish this act is still one of considerable debate.
The dorsal position
The dorsal lithotomy position is the one used commonly in North America. However, it is noteworthy that it only came into use within the last 150 years or so, and is not recommended in any other region of the world. In fact, what is today termed the conventional birthing position is actually the exception, with more vertical orientations being the norm almost everywhere else. Only 18 percent of cultures reflects the use of the dorsal position for childbirth.
Other positions
Most other maternal birthing positions take advantage of gravity to push down the baby in synchrony with uterine contractions, while also opening the pelvic outlet to facilitate the expulsion of the baby. They also take the weight of the uterus and baby off the great vessels and the uterine vessels in the posterior wall of the abdomen.
They give the woman a better view of what is occurring and enable her to participate actively in the labor and delivery. Contractions are often more frequent and stronger with the labouring woman in one of these positions, and the likelihood of fetal distress is lower. The upright and left lateral positions are associated with the lowest risk of maternal perineal tears.
The standing position
This upright position is highly ergonomic, in that it enables the action of gravity to enhance the effect of the contractions and of maternal pushing, in helping the baby to navigate the curved pelvic cavity. It is associated with the lowest risk of anal sphincter injuries during childbirth.
This position also relieves the uterine vessels and the inferior vena cava from the weight of the gravid and contracting uterus. This prevents any reduction in maternal blood flow and resulting placental ischemia, which could produce fetal distress. Like all vertical positions, it encourages greater frequency of contractions. It is, however, inconvenient for the obstetrician to see or assist the process of delivery in this position.
The semi-reclining position
The reclining position came into favor in the 1600s, largely due to the influence of Mauriceau, who was among the earliest of the barber-surgeons to be actively involved in obstetrics. It may have some connection with the fact that this was also the period of the emergence of lithotomy, which required this precise view of the perineum.
Historically, it is clear that these two innovations became popular at the same time, but no documentary evidence exists of their relationship. This position keeps the woman visible and gives her greater control of the birthing process. It also utilizes some advantage of gravity. By the 1800s this was commonplace in French confinements.
The left lateral position
In England, however, the lateral decubitus position was in favor still. This allows the woman to rest between pushes while still allowing the birth attendant to have a clear view of and assist with the emergence of the baby. It is not so physiological as the upright position with respect to the mechanics of descent of the presenting part, but the risk of perineal tears is relatively low. It is also found to produce the strongest contractions among all birthing positions.
Alternating between the semi-reclining or sitting, and left lateral positions is found to have the best outcome of all. All vertical positions produce a higher resting pressure within the uterine muscle which shortens the process of labor. It helps the tired parturient recover strength, is useful in relieving fetal distress, and to augment the second stage.
Squatting and the birthing stool
German women used the birthing stool extensively. There is ancient evidence of the use of birthing stools to support the mother in a squatting position during labor and delivery, with pictures of its use dating back to Babylonian times (c. 2000 BC). This position, with the spine erect and the thighs abducted, helps to open the pelvis maximally, directing the weight downward on the sacrum. The symphysis pubis and the sacroiliac joints are thrust outwards along with the backward motion of the sacrum and coccyx.
As a result, squatting results in an increase in pelvic outlet size by 28 percent. One should note that most traditional birthing postures, namely, squatting, kneeling, and using a birthing stool, all produce the same effect. However, these are associated with an increased incidence of perineal injury compared to the standing or lateral position.
The sitting position
The sitting position makes full use of the ergonomic advantages of gravity, and relieves lower back pain. It helps the woman move her legs freely, and the birthing chair also offers the birth attendant good visibility of the perineum.
The kneeling and the all-fours position
Many women are not able to kneel or squat for long in developed countries, but the all-fours position helps to relieve the strain on the back, and to push down better in the second stage.
Disadvantages
As mentioned above, the dorsal lithotomy position is associated with greatest convenience for the birth attendant - the others offer less visibility. In addition, it is easiest to auscultate the fetal heart in the dorsal position whilst in the other positions, electronic fetal monitoring may be needed. The administration of epidural anesthesia makes the other positions more difficult to maintain, but the left lateral decubitus position is viable and convenient.
It is undisputed that most of the so-called alternative birthing positions do have distinct and multiple physiologic advantages which make labor easier and shorter. For this reason, the ease of childbirth and the comfort of the laboring woman should be paramount in the choice of position, rather than only the convenience of the birth attendant.
References
Further Reading
Fetal hormone GDF15 linked to nausea and vomiting in pregnancy