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Pelvimetry
 
 
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Pelvimetry is the assessment of the female pelvis
Pelvis

The pelvis or pelvic girdle is the irregular bone structure located at the base of the spine . In the adult human, it is formed by the sacrum and the coccyx, the caudal part of the axial skeleton, and a pair of hip bones, part of the appendicular skeleton or human leg....
 in relation to the birth
Birth

Birth is the act or process of bearing or bringing forth offspring . The offspring is brought forth from the mother. Different forms of birth are oviparity, vivipary or Ovoviviparity....
 of a baby. Traditional obstetrical services relied heavily on pelvimetry in the conduct of delivery in order to decide if natural or operative vaginal delivery
Childbirth

Childbirth is the culmination of a human pregnancy or gestation period with the delivery of one or more newborn infants from a woman's uterus. The process of normal human childbirth is categorized in three stages of labour: the shortening and dilation of the cervix, descent and delivery of the infant, and delivery of the placenta.....
 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.

imetry used to be performed routinely to discern if spontaneous labour was medically advisable.






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Pelvimetry is the assessment of the female pelvis
Pelvis

The pelvis or pelvic girdle is the irregular bone structure located at the base of the spine . In the adult human, it is formed by the sacrum and the coccyx, the caudal part of the axial skeleton, and a pair of hip bones, part of the appendicular skeleton or human leg....
 in relation to the birth
Birth

Birth is the act or process of bearing or bringing forth offspring . The offspring is brought forth from the mother. Different forms of birth are oviparity, vivipary or Ovoviviparity....
 of a baby. Traditional obstetrical services relied heavily on pelvimetry in the conduct of delivery in order to decide if natural or operative vaginal delivery
Childbirth

Childbirth is the culmination of a human pregnancy or gestation period with the delivery of one or more newborn infants from a woman's uterus. The process of normal human childbirth is categorized in three stages of labour: the shortening and dilation of the cervix, descent and delivery of the infant, and delivery of the placenta.....
 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.

Use

Pelvimetry used to be performed routinely to discern if spontaneous labour was medically advisable. Women whose pelvises were deemed too small received caesarean sections instead of birthing naturally. Research indicates that pelvimetry is not a useful diagnostic tool for CPD (see below) and that in all cases spontaneous labour and birthing should be facilitated. See Blackadar & Viera, 2003, p505

A woman's pelvis loosens 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 lithotomy (lying on her back, head of bed elevated) is more than likely not going to push a larger than average baby out, due to the size of outlet that this position creates. Since obstetricians continue to place women in this position for their requirement of 'access', not considering the birthing mother's needs to be in a better position to open her pelvis, it is more likely that women will be given a potentially false diagnosis that their pelvis is too small to birth their baby.

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
Rickets

Rickets is a softening of bones in children potentially leading to fractures and deformity. Rickets is among the most frequent childhood diseases in many developing countries....
 or a pelvic fracture
Fracture

A fracture is the separation of an object or material into two, or more, pieces under the action of stress .The word fracture is often applied to bones of living creatures, or to crystals or crystalline materials, such as gemstones or metal....
, and lead to CPD.

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
Radiography

Radiography is the use of X-rays to view unseen or hard-to-image objects. The main diagnostic purposes of X-rays are to see inside one's body, most commonly the bones which can be viewed at an optimum resolution ....
 and MRI.

Pelvic planes

  • Pelvic inlet
    Pelvic inlet

    The superior circumference of the lesser pelvis forms the brim of the pelvis, the included space being called the superior aperture or pelvic inlet....
    : The line between the narrowest bony points formed by the sacral promontory
    Sacral promontory

    The sacral promontory is the anatomical term for the superiormost portion of the sacrum. It marks part of the border of the pelvic inlet.With the iliopectineal line, it comprises the linea terminalis....
     and the inner 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
    Pubic arch

    The eminences of the lower circumference of the true pelvis are separated by three notches: one in front, the pubic arch, formed by the convergence of the inferior rami of the ischium and pubis on either side....
     to sacral promontory). The transverse diameter of the pelvic inlet measures 13.5 cm.
  • Midpelvis: The line between the narrowest bone points connects the ischial spine
    Ischial spine

    From the posterior border of the body of the Ischium there extends backward a thin and pointed triangular eminence, the ischial spine, more or less elongated in different subjects....
    s; it typically exceeds 12 cm.
  • Pelvic outlet
    Pelvic outlet

    The lower circumference of the lesser pelvis is very irregular; the space enclosed by it is named the inferior aperture or 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.


See also

  • Childbirth
    Childbirth

    Childbirth is the culmination of a human pregnancy or gestation period with the delivery of one or more newborn infants from a woman's uterus. The process of normal human childbirth is categorized in three stages of labour: the shortening and dilation of the cervix, descent and delivery of the infant, and delivery of the placenta.....
  • List of obstetric topics
    List of obstetric topics

    Obstetrics is the study of the reproductive process within the female body, including fertilization, pregnancy and childbirth....
  • Pelvic Bone Width
  • Pelvis
    Pelvis

    The pelvis or pelvic girdle is the irregular bone structure located at the base of the spine . In the adult human, it is formed by the sacrum and the coccyx, the caudal part of the axial skeleton, and a pair of hip bones, part of the appendicular skeleton or human leg....
  • Pregnancy
    Pregnancy

    Pregnancy is the carrying of one or more offspring, known as a fetus or embryo, inside the uterus of a female. In a pregnancy, there can be multiple gestations, as in the case of twins or Multiple birth....
  • Sacroiliac joint
    Sacroiliac joint

    The sacroiliac joint or SI joint is the joint between the sacrum, at the base of the vertebral column and the ilium of the pelvis, which are joined by ligaments....
  • Sacrum
    Sacrum

    The sacrum is a large, triangular bone at the base of the vertebral column and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones....
  • Symphysis pubis