Pelvimetry - Women

May 23, 2012


		1 Introduction 2 Use 3 Cephalo-pelvic disproportion: CPD 4 Terminology 5 See also 6 References

Women Women

Pelvimetry

Wikipedia

Pelvimetry is the assessment of the female pelvis is relation to the birth of a baby. Traditional obstetrical services relied heavily on pelvimetry in the conduct of delivery in order to decide if natural or operative childbirth|vaginal delivery was possible or if and when to use a cesarean section. With the increased safety of modern cesarean section and increased medico legal concerns about use of operative vaginal delivery, the threshold to perform a cesarean section has decreased and the need for pelvimetry diminished.

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Use

Pelvimetry used to be performed routinely to see if a trial of labour (childbirth)|labour should be allowed. Women whose pelvis were deemed too small were given caesarean section's instead of being allowed to birth naturally. Research indicates that pelvimetry is not a useful diagnostic tool for CPD (see below) and then in all cases trial of labour should be allowed. See Blackadar & Viera, 2003, p505

Women's pelvis loosen up before birth (with the help of hormones), and an upright and/or squatting woman can birth a considerably larger baby. A woman in the 'stranded beetle position' (lying on her back) it is more than likely not going to push a bigger baby out, due to the size of outlet that this position creates. Since obstetricians continue to place women in this torturous position for their own personal requirement of 'access', not considering the birthing mother's needs to be in a better position to open her pelvis, it is inevitable that women will be subjected to the false diagnosis that their pelvis is too small to birth their baby.

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Cephalo-pelvic disproportion: CPD

Cephalo-pelvic disproportion exists when the capacity of the pelvis is inadequate to allow the fetus to negotiate the birth canal. This may be due to a small pelvis, a nongynecoid (see below) pelvic formation, or a large fetus, and combinations of these. Certain medical conditions may distort pelvic bones, such as rickets or a pelvic fracture, and lead to CPD.

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Terminology

The terms used in pelvimetry are commonly used in obstetrics. Clinical pelvimetry attempts to assess the pelvis by clinical examination. Pelvimetry can also be done by radiography and MRI.

Pelvic planes

Pelvic inlet: The line between the narrowest bony points formed by the sacral promontory and the inner pubic bone|pubic arch is termed obstetrical conjugate: It should be 11.5 cm or more. This anteroposterior line at the inlet is 2 cm less than the diagonal conjugate (distance from undersurface of pubic arch to sacral promontory).

Midpelvis: The line between the narrowest bone points connects the ischial spines; it typically exceeds 12 cm.

Pelvic outlet: The distance between the ischial tuberosities (normally > 10 cm), and the angulation of the pubic arch.

Pelvic types
Traditional obstetrics characterizes four types of pelvises:

Gynecoid: Ideal shape, with round to slightly oval (obstetrical inlet slightly less transverse) inlet: best chances for normal vaginal delivery.

Android: triangular inlet, and prominent ischial spines, more angulated pubic arch.

Anthropoid: inlet transverse is greater than inlet obstetrical diameter.

Platypelloid: Flat inlet with shortened obstetrical diameter.

Fetal relationship

Engagement: The fetal is engaged if the widest leading part (typically the widest circumference of the head) is negotiating the inlet.

Station: Relationship of the leading bony part of the fetus to the maternal ischial spines. If at the level of the spines it is at ???0(zero)??? station, if it passed it by 2 cm it is at ???+2??? station.

Attitude: Relationship of fetal head to spine: flexed, neutral (???military???), or extended attitudes are possible.

Position: Relationship of presenting part to maternal pelvis, i.e. ROP=right occiput posterior, or LOA=left occiput anterior.

Presentation: Relationship between the leading fetal part and the pelvic inlet: cephalic, breech, or shoulder presentation.

Lie: Relationship between the longitudinal axis of fetus and mother: longitudinal, oblique, and transverse.

Caput or Caput succedaneum: edema typically formed by the tissue overlying the fetal skull during the vaginal birthing process.

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