Pelvimetry is the assessment of the female pelvisis relation to the birthof a baby. Traditional obstetrical services relied heavily on pelvimetry in the conduct of delivery in order to decide if natural or operative vaginal deliverywas 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.
- 1 Use
- 2 Cephalo-pelvic disproportion: CPD
- 3 Terminology
- 3.1 Pelvic planes
- 3.2 Pelvic types
- 3.3 Fetal relationship
- 4 See also
- 5 References
Pelvimetry used to be performed routinely to see if a trial of labourshould be allowed. Women whose pelvis were deemed to 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
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 a ricketsor a pelvic fracture, and lead to CPD.
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 radiographyand MRI.
- Pelvic inlet: The line between the narrowest bony points formed by the sacral promontoryand the inner pubic archis 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.
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.
- 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.
- List of obstetric topics
- Scott JR, Gibbs RS, Karlan BY, Haney AF: Danforth?s Obsterics and Gynecology. 9th edition. Lippincott Williams and Wilkins, Philadelphia. USA , 2003.
- Blackadar CS, Viera A: "A Retrospective Review of Performance and Utility of Routine Clinical Pelvimetry", AAFP, 2003, v36:7, p505 
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It uses material from the Wikipedia article Pelvimetry.