United Brachial Plexus Network, Inc.

By increasing space in the pelvis, the all-fours position can fix shoulder dystocia and encourage a baby to move from the posterior position to the proper fetal positioning. (Bruner, J.P., et al. All-fours maneuver for reducing shoulder dystocia during labor. J Reprod Med 1998;43(5):439-443)

Walking opens the inlet of the pelvis and speeds labor by 28%, almost as much as Pitocin. (Dr. Roberto Caldyero-Barcia, Italian physician and researcher)

The incidence of persistent posterior babies increases by 450 percent with epidural use. (Epidural vs. non- epidural analgesia in labor. In: Neilson, J.P. et al. eds. Pregnancy and Childbirth Module of the Cochrane Database of Systematic Reviews, updated September 1997)

and the definition of shoulder dystocia is all over the board:

http://ajol.info/index.php/sajog/articl ... 0343/39030
Shoulder dystocia arises when the shoulders are too broad to pass through the pelvic outlet simultaneously, and fundal pressure alone or direct traction to the baby’s head does not help to deliver the shoulders and body.


If the mother is push- ing well and the shoulders have rotated, the birth can be ac- complished with gentle traction by the birth attendant. If the shoulders have not rotated, the pelvic outlet is small, the infant is malpositioned (nuchal hand or arm), or the shoulders and chest are a larger circumference than the head, it’s probable that shoulder dystocia will occur (Gherman, 2005).


Which is "normally" bigger, pelvic outlet or pelvic inlet? Pelvic inlet:
http://emedicine.medscape.com/article/260036-overview

The pelvis can also be assessed either by clinical examination (clinical pelvimetry) or radiographically (CT or MRI). The pelvic planes include the following:

* Pelvic inlet: The obstetrical conjugate is the distance between the sacral promontory and the inner pubic arch; it should measure 11.5 cm or more. The diagonal conjugate is the distance from the undersurface of the pubic arch to sacral promontory; it is 2 cm longer than the obstetrical conjugate. The transverse diameter of the pelvic inlet measures 13.5 cm.
* Midpelvis: The midpelvis is the distance between the bony points of ischial spines, and it typically exceeds 12 cm.
* Pelvic outlet: The pelvic outlet is the distance between the ischial tuberosities and the pubic arch. It usually exceeds 10 cm.

http://ps.mcicvermont.com/appdocs/lps/Should Dystocia_the nurse's role AWHONN 2007 .pdf
Positioning of the mother is important in all births but even more so when a large baby is expected and shoulder dys- tocia is more likely than usual. The mother of a macrosomic infant may push more effectively on either side, but at the time of birth the mother should either be squatting, on her hands and knees, or semi-sitting. This enables the physician or mid- wife to attempt to continue the delivery of the head and shoul- ders in one motion, rather than spending time stopping for a contraction, cutting the cord or suctioning the baby.

...'Keeping this IMPORTANT INFORMATION up front.... We have a number of new moms-to-be recently joined our UBPN Family.
UBPN IS a Caring, Informed Family!
Carolyn J
LOBPI/72

The tailbone is not relevant until both shoulders have passed through the pubic inlet. In normal childbirth, the posterior shoulder passes through the inlet first and rests in the sacral hollow. The anterior shoulder then rotates to the oblique axis, fitting under the pubic symphysis and joining the posterior shoulder in the mid-pelvis. The anterior shoulder is then normally birthed through the outlet (perineum) first (unless the posterior arm is deliberately gone after and "swept" out to alleviate shoulder dystocia) after this "swivel" of the shoulders and fetal body occurs. The concepts of "inlet" and "outlet" are confusing when discussion shoulder distocia because the shoulders don't both go through either at exactly the same time. They "take turns". I have not seen any research that indicates that pressure on the tailbone decreases the space in the midpelvis, where the posterior shoulder sits while waiting for the anterior shoulder to pass under the pubic bone. Pressure on the tailbone could make it more difficult for the anterior shoulder to be delivered AFTER it clears the pubic symphysis, but this is not the distocia that typically causes injury.

A good explanation of the mechanics of birth is in this article discussing delivery of the posterior arm for shoulder dystocia. Note that the posterior arm must be *deliberately delivered*. It DOES NOT comes out first naturally, without intervention. The anterior shoulder comes out first. This further supports that obstruction at the tailbone - which would impeded delivery of the posterior arm, is NOT the cause of impaction of the anterior arm, which is the severe dystocia that causes most injuries:

http://www.obgyn.net/women/women.asp?pa ... casereport

"Discussion

Recalling the mechanism of normal delivery is the key to understanding what occurs in shoulder dystocia. It is important to remember that although the bisacromial diameter of a fully grown term fetus is greater than the biparietal diameter, the shoulders are mobile and compressible and the pelvic inlet is normally wider in the oblique diameter than the posterior. During labour, uterine contractions lead to flexion and engagement of the fetal head, if this hasn’t occurred already. The head enters the pelvis inlet in the occipitotransverse position, with the shoulders lying anterioposterior at this stage. Internal rotation of the head occurs as the head reaches the level of the ischial spines, while the shoulders rotate to the oblique position. Fetal head extends as it comes through the pelvic outlet. The shoulders pass through the pelvic inlet in the oblique position. The posterior shoulder enters first, coming to rest in the sacral hollow or over the sacrosciatic notch, while the anterior shoulder follows it to lie over the obturator foramen. As further descent occurs, the anterior shoulder emerges from under pubic ramusand the shoulder girdle rotates to allow delivery in the anterioposterior position, which is usually assisted by lateral flexion of the body. It is important to appreciate that, in shoulder dystocia, the point of obstruction occurs at the inlet of the pelvis. Usually the posterior shoulder enters the pelvis, but the anterior shoulder, having failed to rotate to the oblique position, remains trapped behind the symphysis pubis. Once the shoulders impact at the pelvis inlet, the fetal head which has already left the pelvis, often recoils tightly against the maternal perineum. This is termed the ‘Turtle sign’, and as in Mrs AN’s case, it was the first sign of shoulder dystocia occurring (Sturdee et al, 2001)."

The fetus can only become impacted against both the pubic symphysis (anterior arm) AND the tip of the tailbone (posterior arm) if the brachial plexus is already significantly stretched and the shoulders tilted severely with respect to the head. Yes, the baby can impact against both the pubic bone and the tailbone... if the doctor has pulled on them so severely. In that case they are likely to already have an injury. Just look at this image and how much stretch on the anterior shoulder would be necessary to get the posterior shoulder to the outlet with the anterior shoulder still behind the pubic symphysis. It just isn't physiological:

http://www.smartimagebase.com/shoulder- ... temID=8896

Or look at any other picture of a fetus in the birth canal. It is not possible to birth the posterior shoulder past the sacral promontary without stretching the brachial plexus to get the shoulder it that far. When the posterior arm is delivered first, it is the posterior ARM, not the posterior SHOULDER, that comes out first. Getting the posterior arm out the outlet decreases the bisacromial diameter of the shoulders, allowing the anterior shoulder to rotate and pass the pubic bone into the mid-pelvis, where the baby can then be delivered. .

http://www.trialimagestore.com/article_ ... ticle.html
http://www.smartimagebase.com/manipulat ... temID=7121

Note how at no point is the tailbone the thing that is blocking the baby.

Kate

Posting again to bring thisimportant information up front for new Moms-to-Be who come here.
Carolyn J
LOBPI/72