Maternal Pelvis

Ans. is a i.e. Interspinous diameter of the outlet

Interspinous diameter is the distance between the two ischial spines and is the smallest diameter of the pelvis 10 cms. It corresponds to the transverse diameter n^f mid pelvis (i.e. plane of least pelvis dimensions).

Plane of least pelvis dimensions is of particular importance in labour as :

• Internal rotation occurs at this level.°
• It marks the beginning of the forward curve of the pelvic axis.°
• Most cases of deep transverse arrest occur here.°
• Ischia’ spines represent zero station of the head.°
• External os is at this level.°

Besides these : It corresponds to origin of levator ani muscle° and is a landmark used for pudendal block°.

Also know : Another important diameter of pelvis is the Posterior Sagittal diameter of the outlet as the prognosis for vaginal delivery in case of narrowing of midpelvis or pelvic outlet depends on it.

Ans. is a and c i.e. Narrow sciatic notch and Subpubic angle is acute

Important differentiating feature between male and female pelvis are :

1. General built                                    Massive, rough with                                       Slender, smooth, bones are light

Marked bony prominences               with bony markings less Prominent

2.   General Shape                              Deep funnel                                                    Flat bowl

3.   Pelvic brim or inlet                        Heart — shaped.                                            Circular or elliptical; more spacious; diameters longer.

4.   Pelvic cavity                                   Conical and funnel — shaped.                    Broad and round.

5.   Pelvic outlet                                    Smaller                                                             Larger

Features Narrow I small in male pelvis and broad / big in female pelvis :

• Preauricular sulcus (not frequently seen in male pelvis and if present at all it is narrow and shallow).
• Greater sciatic notch
• Body of pubis
• Subpubic angle :              In male pelvis – it is V shaped and ranges b/w 70-75°.

—      In female pelvis it is U shaped and ranges between 90-100.°

• lschial Tuberosity             Inverted and less widely separated in male pelvis while it is everted and more widely separated in female.

Features large / well marked in male pelvis and small/less marked in female pelvis :

• Obturator foramen (large and oval shaped in male pelvis and small and triangular in female pelvis)
• Ileopectineal line (well marked in male pelvis)
• Sacroiliac joint surface (large in male pelvis)
• Promontory (well marked in male pelvis).

• Long and narrow in male pelvis
• Short and wide in female pelvis
• Less movable in male pelvis
• More movable in female pelvis

Transverse diameter

Diagonal conjugate

2.0 cm

Lower part of pelvis

Posterior sagittal diameter

Lower border of symphysis pubis and the sacral Promontory

Interspinous diameter of 10.5 cm is the shortest of the true pelvic diameters amongst the options provided.

Ref:Textbook of Gynecology By D C Dutta, 6th Edition, Page 91

The smallest diameter of the midpelvis or midplane is the transverse or interspinous diameter (10cm or more) which is between the two ischial spines. 

Pelvis are classified as belonging to one of four major groups.

The gynecoid pelvis is the classic female pelvis with a posterior sagittal diameter of the inlet only slightly shorter than the anterior sagittal diameter.

In the android pelvis, the posterior sagittal diameter at the inlet is much shorter than the anterior sagittal diameter, limiting the use of the posterior space by the fetal head.

In the anthropoid pelvis, the anteroposterior (AP) diameter of the inlet is greater than the transverse diameter, resulting in an oval with large sacrosciatic notches and convergent side walls. Ischial spines are likely to be prominent.

The platypelloid pelvis is flattened with a short AP and wide transverse diameter. Wide sacrosciatic notches are common. The pelves of most women do not fall into a pure type and are blends of one or more of the above types.

Ans. is C. Obstetric conjugate

The obstetric conjugate is the shortest distance between the promontory of the sacrum and the symphysis pubis.

It generally measures 10.5 cm. Because the obstetric conjugate cannot be clinically measured, it is estimated by subtracting 1.5 to 2 cm from the diagonal conjugate, which is the distance from the lower margin of the symphysis to the sacral promontory.

The true conjugate is measured from the top of the symphysis to the sacral promontory.

The interspinous diameter is the transverse measurement of the midplane and generally is the smallest diameter of the pelvis. 

 Ans. is B. i.e. Android pelvis

• The android pelvis has a wedge-shaped inlet, a narrow fore pelvis, a flat posterior segment, and a narrow sacrosciatic notch, with the sacrum inclining forward. 
• The side walls converge, and the bones are medium to heavy in structure.
• The diameter of engagement is transverse or oblique. 
• Anterior rotation is difficult in the android type. The chance of arrest is present.

Gynecoid is the most common type of female pelvis. In this type of pelvis the inlet is oval or round.

In the midpelvis, sides of the pelvis are straight and the spines are not prominent.

At the outlet the pubic arch is wide and the sacrum is neither inclined anteriorly nor posteriorly.

The configuration of this type of pelvis suits well for the delivery of the fetus.

• Gynecoid
• Android
• Anthropoid
• Platypelloid

Ans. is C. i.e. 85°

A subpubic angle of 50-82 degrees indicates a male; an angle of 90 degrees indicates a female.

Other sources operate with 50-60 degrees for males and 70-90 degrees in females.

Women have wider hips, and thus a greater subpubic angle, to allow for childbirth.

Ans. C: Diagonal conjugate

Ans. B: 10.5

Transverse diameter of the mid-pelvis/ bispinous (10.5): It measures between the 2 ischial spines Diameters:

Shortest diameter of pelvic inlet: Obstetrical conjugate

2nd Shortest diameter of fetal skull: Bitemporal

2nd Largest diameter of fetal skull: Submentovertical

Ans. C: Interspinous Diameter

Diagonal conjugate-between the lower border of symphysis pubis to the midpoint on the sacral promontory-12 cm Interspinous (Bispinous) diameter-between the tip of two ischial spines-10.5 cm

lntertuberous diameter-between inner borders of ischial tuberosities-11 cm

Pelvis shape type as shown in the photograph above represents Platypelloid.

Platypelloid Pelvis.

Platypelloid pelvis is has narrow anterio-posterior diameter of pelvic inlet. The pelvic inlet is specifically kidney shaped. The pelvic cavity is usually shallow and diameters of outlet are favorable for the process of labor. But platypelloid pelvis don’t allow the head to engage with ease. But if the head manage to engage then rest of the process of labor may occur normally but in most of the cases it is longer as compared to progress of labor in case of gynaecoid pelvis.

Gynaecoid Pelvis.

This is the most suitable female pelvic shape. This allow normal child birth with ease. It has round pelvic inlet and shallow pelvic cavity with short ischial spines. All these feature allow rapid birth of the baby. So Gynaecoid Pelvis is the most suitable pelvic shape for childbirth.

 Android Pelvis.

Android shaped pelvis has triangular or heart-shaped inlet and is narrower from the front. It has prominent ishial spines and also has narrower transverse outlet diameter. Such pelvis is more likely to be present in tall women. African-Caribbean women are more at risk of having an adroid shaped pelvis. Child birth is difficult and more complicated in android shaped pelvis than gynaecoid pelvis. Women have to push harder, walk more often and chances of instrumental vaginal delivery are high. It may prolong the labor.

True pelvis is represented by 2,3 and 4.

The green line marked in the pelvis as shown in the picture above represents false pelvis.

The false pelvis supports the intestines (specifically, the ileum and sigmoid colon) and transmits part of their weight to the anterior wall of the abdomen.

Bounded on either side by the ilium; in front it is incomplete, presenting a wide interval between the anterior borders of the ilia; behind is a deep notch on either side between the ilium and the base of the sacrum.