pelvis and labour

Pelvic outlet lies at the level of

ischial tuberosity

Pelvic inlet lies at the level of

pelvic brim

Pelvic cavity lies at the level of

ischial spine

Plane of greatest pelvic dimension—Anterior boundary

Posterior surface of pubic symphysis

Plane of greatest pelvic dimension—Posterior boundary

Junction of S2-S3

Plane of greatest pelvic dimension—Lateral boundary

Obturator foramen

Diameters of plane of greatest pelvic dimension

12 cm (no obstetric significance)

Plane of least pelvic dimension—Anterior boundary

Lower border of pubic symphysis

Plane of least pelvic dimension—Posterior boundary

Junction of S4-S5

Plane of least pelvic dimension—Lateral boundary

Ischial spines

Plane of least pelvic dimension significance

Narrowest plane of pelvis

AP diameter of plane of least pelvic dimension

11.5–12 cm

Transverse (interischial/bispinous) diameter of plane of least pelvic dimension

10 cm (smallest in pelvis)

Midpelvis definition

Area between plane of greatest and least pelvic dimensions

True conjugate (anatomical conjugate)

Distance between sacral promontory and upper border of pubic symphysis = 11 cm

Obstetric conjugate

Distance between sacral promontory and mid of pubic symphysis = 10.5 cm

Diagonal conjugate

Distance between sacral promontory and lower border of pubic symphysis = 12 cm

Transverse diameter of pelvic inlet

13 cm

Oblique diameter of pelvic inlet

12 cm (between sacroiliac joint and opposite iliopectineal eminence)

Anatomical outlet boundaries—Anterior

Lower border of pubic symphysis

Anatomical outlet boundaries—Posterior

Tip of coccyx

Anatomical outlet boundaries—Lateral

Ischial tuberosities

AP diameter of outlet

13 cm

Transverse diameter of outlet (bituberous diameter)

11 cm

Obstetric outlet definition

Space between plane of least pelvic dimensions and anatomical outlet

Clinically measurable AP diameter of inlet

Diagonal conjugate

Critical obstetric conjugate value for vaginal delivery

If diagonal conjugate = x cm, obstetric conjugate =

x – 1.5 cm

Overall most important diameter for labour

Interischial diameter

Angle of pelvic inclination

55°

Subpubic angle difference

Male—acute; Female—obtuse

Contracted pelvis definition

Any major pelvic diameter decreased by 1 cm or specific criteria met

Contracted inlet criterion

Obstetric conjugate <10 cm

Contracted midpelvis criterion

Interischial diameter <8 cm

Contracted outlet criterion

Bituberous diameter <8 cm

Management of contracted pelvis

Always cesarean section

Naegele’s pelvis characteristic

Only one sacral ala present (one absent)

Robert pelvis characteristic

Both sacral alae absent

Gynecoid pelvis percentage

50% (most common)

Android pelvis percentage

20% (male pelvis type)

Anthropoid pelvis percentage

25%

Platypelloid pelvis percentage

5% (least common)

Gynecoid pelvis inlet shape

Transversely oval

Android pelvis inlet shape

Heart shaped

Anthropoid pelvis inlet shape

Anteroposteriorly oval

Platypelloid pelvis inlet shape

Flat, wide

Gynecoid pelvis diameters

Transverse > AP

Android pelvis diameters

Transverse > AP

Anthropoid pelvis diameters

AP > Transverse

Platypelloid pelvis diameters

Transverse >>> AP

Ischial spine prominence among pelvic types

Prominent in Android pelvis

Subpubic angle in Gynecoid vs Android

Gynecoid—obtuse; Android—acute

Most common presentation in Gynecoid

Occipitoposterior (OP)

Most common presentation in Android

Persistent OP

Most common presentation in Anthropoid

Direct OP

Most common presentation in Platypelloid

Face to pubis

Most favorable pelvis for delivery

Gynecoid

Least favorable pelvis for delivery

Android

Definition of lie

Relation of long axis of fetus to that of uterus

Most common lie

Longitudinal

Most common presentation

Cephalic

Most common malpresentation

Breech

Presentation in transverse lie

Shoulder

Management of transverse lie—antenatal

External cephalic version at 36 weeks

Management of transverse lie—in labour

C-section

Transverse lie with dead baby (neglected shoulder presentation)

C-section

Most common congenital anomaly with face presentation

Anencephaly

Most common presenting part in anencephaly

Face

Angle of pelvic inclination

55°

AP diameter of engagement (vertex)

Suboccipitobregmatic (9.5 cm)

AP diameter of engagement (brow)

Mentovetical (14 cm)

AP diameter of engagement (face)

Submentobregmatic/Submentovertex (9.5 cm)

Delivery in vertex presentation

Vaginal

Delivery in brow presentation

C-section

Delivery in face presentation

If mentoanterior—vaginal; If mentoposterior—C-section

Definition of position

Relationship of denominator to maternal pelvis

Denominator in cephalic presentation

Occiput

Most common position in breech

Left sacroanterior

Most common position in face

Left mentoanterior

Maximum risk of cord prolapse

Transverse lie

Most common occipitoanterior position

LOA

Most common occipitoposterior position

ROP

Occipitoposterior position management

Wait and watch

Station definition

Position of fetal head with respect to ischial spines

Forceps can be applied at station

+2 or below

Lie requirement for delivery

Uterus parallel to vertebrae (not dextrorotated)

Difference between Caput succedaneum and Cephalhematoma—Type of collection

Caput—Fluid; Cephalhematoma—Blood

Caput succedaneum cause

Prolonged labour pressure

Cephalhematoma cause

Traumatic instrumental delivery

Caput succedaneum location

Above periosteum (crosses sutures)

Cephalhematoma location

Below periosteum (does not cross sutures)

Pitting on pressure—Caput vs Cephalhematoma

Caput—Yes; Cephalhematoma—No

Association with fracture—Caput vs Cephalhematoma

Caput—No; Cephalhematoma—Yes

Time of appearance—Caput vs Cephalhematoma

Caput—At birth; Cephalhematoma—Hours after birth

Resolution time—Caput vs Cephalhematoma

Caput—2–3 days; Cephalhematoma—2–3 weeks

1st Leopold’s maneuver

Fundal grip → checks lie & presentation

2nd Leopold’s maneuver

Lateral grip → checks position (back vs limbs)

3rd Leopold’s maneuver

Pawlik grip → checks presentation & engagement

4th Leopold’s maneuver

Deep pelvic grip → confirms attitude & engagement

Bishop’s score purpose

To assess cervical readiness for induction of labour (IOL)