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Bukovinian State Medical University

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Bukovinian State Medical University


on methodological meeting

of Department of Obstetrics and Gynecology

with course of Infant and Adolescent Gynecology

“___”______________________ 200_ year

protocol #

The Head of the department

Assistant Professor

________________ S.P.Poliova

Methodological instruction

for practical lesson

“Bony pelvis. Fetus as an object of labor”

Module 1: Physiology of pregnancy, labor and puerperium

Context module 1: Physiology of pregnancy, labor and puerperium

Subject: Obstetrics and Gynecology

4th year of studying

2nd medical faculty

Number of academic hours – 4

Methodological instruction developed by:

assistant Andriy Berbets

Chernivtsi – 2008

Aim; to learn measuring the pelvis sizes, to estimate pelvis from the obstetrics' point of view, to learn the structure of pelvic floor, sizes of fetus head.

Basic level:

1. Structure of pelvis.

2, Main anatomic landmarks for measuring pelvis.

3. Shape and sizes of pelvic planes.

4. External sizes of pelvis.

5. Structure of pelvic floor.

6. Structure and sizes of in-term fetus head.

Inter-subject integration

Previous disciplines

Requested skills


To describe anatomy of female pelvis, external and internal female genitalia, pelvic floor, to define parts pf pelvis and their dimensions. To know the dimensions of fetal head


I. Objectives for Students' Independent Studies

You should prepare for the practical class using the existing textbooks and lectures. Special attention should be paid to the following:

1. What bones is the pelvis consist of?

2. Differences between female and male pelvis.

3. The main landmarks of the female pelvis.

4. Planes of pelvis and their sizes.

5. Main and additional external pelvis sizes.

6. Methods of estimation of true conjugate.

7. Solovjov index. It’s significance for estimation of internal pelvic sizes.

8. Mikhaelis rhomb. Its significance for estimation of result of labor.

9. Structure of pelvic floor.

10. Structure and sizes of fetal head.

11. Body sizes of in-term fetus,

12. Sutures and fontanels and their significance for diagnosing the situation of fetal head.

13. Definition of «large segment» of fetal head.

14. Relationship of fetal head to pelvic planes.

Key words and phrases: Bony pelvis, pelvic inlet, greatest diameter, midplane, pelvic outlet, anterior and posterior fontanels; occipitofrontal dimension, subocccipitobregmatic diameter, occipitomental dimention; biparietal, bitemporal distance; sagittal, frontal, lambdoid suture.

^ Summary

Planes and Diameters of the Pelvis.

The pelvis has four imaginary planes:

1 - plane of the pelvic inlet,

2 - plane of greatest pelvic dimensions,

3 - the plane of the midpelvis (least pelvic dimensions),

4 - the plane of the pelvic outlet.

Pelvic inlet is bounded posteriorly by the promontory, laterally by the linea terminaiis, and anteriorly by the horizontal rami of the pubic bones and symphysis pubis. Four diameters of pelvic inlet are described: the anterposterior (l 1cm), the transverse (13cm), and two obliques (12 cm from left or right sacroiliac synchondroses to the iliopectineai eminence on the opposite side of the pelvis).

The plane of greatest pelvic dimension extends from the middle of the posterior surface of the symphysis pubis through the ischial bones over the middle of the acetabulum to the junction of second and third sacral vertebrae. Its anteroposterior and transverse diameters are 12,5 cm.

The midpelvis at the level of the ischial spines is particular importance following engagement of the fetus head in obstructed labor. The transverse diameter (interspinous) is 10,5 cm and anteroposterior is 11cm.

Pelvic outlet has two diameters: anteroposterior extends from the lower margin of the symphysis pubis to the tip of the coccys (9,5cm) and transverse diameter between the inner edges of the ischial tuberosities 11,5 cm.

^ The main external pelvic sizes:

D. Spinarun - distance between anterior superior iliac spines from both sides. It has 25-26 cm.

D. Crlstarum ~ distance between iliac crista from both sides. It is 28-29 cm.

D. Trochanterica - distance between trochanter majors from both sides. It has 31-32 cm.

^ C. Externa - distance between midpoint of superior surface of the symphysis pubis and suprasacralis fossa.

Michael's' rhomb. It has 4 angles. The upper angle is located in the suprasacralis fossa. The lower angle is situated in the apex of coccyx, and laterally angles are situated in the posterior superior iliac spines. In the women with normal pelvis rhomb has regular form. It vertical size has 11 cm, and horizontal size is 10 cm.

^ Solovjov' index. It is estimated by the circumference of radiocarpal joint. It has 14-16 cm and indicates into bones' pelvic thickness.

The additional external pelvic sizes:

Lateral conjugate —is a distance between the anterior superior iliac spine and posterior superior iliac spine of the same iliac bone. It has 14.5-16 cm

Oblique conjugate -is a distance between the right anterior superior iliac spine to the left posterior superior iliac spine. It has 14.5-16 cm

Anteroposterior diameter of the pelvic outlet is a distance between the lower part of symphysis pubis and apex of the coccyx. It has 9.5 a

Transverse diameter of the pelvic outlet is a distance between t posterior portions of the ishial tuberosities. It has 11.5 cm.

The main internal pelvic sizes:

The widest anteroposterior diameter of the pelvic inlet is called obstetric conjugate. It runs from the upper midpoint of the symphysis to the promontorium. It has 11 cm. It is one of the most important pelvic dimension.

^ Indirect ways of true conjugate estimation:

1. An estimate of the obstetric conjugate is made by determining the diagonal conjugate. During a vaginal examination, the physician tries to reach the sacral promontory with the middle finger of the examining, hand. The index finger of the free hand marks the point where the lowt border of the pubic symphysis impinges on the examining hand proximal 1 the metacarpophalangeal joint of the index finger. This measurement, th diagonal conjugate, usually exceeds the obstetric conjugate by 1.5 to 2 en

2. External conjugate exceeds the obstetric conjugate by 9 cm.

3. Vertical dimension of Michael's, rhomb equal obstetric conjugate

Fetal head. Obstetrically, the head of fetus is most important part, since an essential feature of labor is an adaptation between the fetal head and the maternal bone pelvis. Only a comparatively small part of the head of the fetus at term is represented by the face; the rest is composed of the firm skull, which is made up of two frontal, two parietal, and two temporal bones, along with the upper portion of the occipital bone and the wings of the sphenoid. The bones are not united rigidly but are separated by membranous spaces, the sutures. The most important sutures are sagittal, between the two pariete bones, frontal between the two frontal bones, the two coronal, between the frontal and parietal bones; and the two lambdoid, between the posterior margin of the parietal bones and upper margin of the occipital bone.

Where several sutures meet an irregular space forms, which is enclosed by a membrane and designated a fontanel. The greater, or anterior fontanel is a lozenge-shaped space situated at the junction of the sagittal and coronal sutures. The lesser, or posterior fontanel is represented by a small triangular area at the intersection of the sagittal and lambdoid sutures. Both may be felt readily during labor, and their recognition gives important information concerning the presentation and position of the fetus.

The circumference and their average lengths are: suboccipitobregrnatic 32cm (9,5 cm); suboccipitofrontal 33cm (l0cm); occipitomental 38cm (13cm); occipitofrontal 34cm (12cm); sublinguobregmatic 32cm (9,5cm), bi parietal (9,5cm); bitemporal (8cm). Circumferences of shoulders is 34cm (12cm), circumferences of pelvic part is 28cm (9,5cm).

^ II. Tests and Assignments for Self - assessment.

Multiple Choice.

Choose the correct answer / statement:

1. The innominate bones are composed of the:

A - Ilium; B - Tibia; C - Ischium; D - Pubis; E - A, B, and C; F - A, C, and D.

2. The false pelvis and true pelvis are separated by the:

A - Acetabulum; B - Sacrospinous ligament; C - Linea terminalis; D - Obturator membrane; E - Obturatory foramen.

3. The false pelvis is separated from the true pelvis by the plane of: A - Pelvic inlet;

B - Greatest diameter;

C - Least diameter;

D - Pelvic outlet.

Real - life situations to be solved:

4. During examination of female pelvis it was reveal that distantia spinarum -26cm, distantia cristarum -29 cm, distantia trochanterica - 30 cm, conjugata externa -21 cm. Solovjovs' index is 15 cm. Definite the size of true conjugate.

III. Answers to the Self- Assessment.

1. F. 2. C. 3. A. 4. Size of true conjugate is 12 cm. Pelvis has normal sizes.

Students must know:

1 .Structure of female pelvis.

2. Planes of true pelvis and their sizes.

3. Main and additional sizes of pelvis.

4. Structure of interm fetus head.

5. Definition of “large segment” of fetal head.

6.Relationship of fetus head to pelvic planes.

Student should be able to:

1.To measure of pelvic sizes. 2.To measure diagonal conjugate. 3.To measure true conjugate.

4.To measure Solovjovs' index and to apply it for estimation of internal sizes of pelvis.

5.To definite the relationship of fetus head to pelvic planes.


1. Danforth's Obstetrics and gynaecology. - Seventh edition- 1994. - P. 108- 112.

2. Basic Gynecology and Obstetrics. - Norman F. Garit F. Gary Cunningham. -1993. - P. 299 - 303


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