Maternal Pelvis

Maternal Pelvis

Divisions of Maternal Pelvis

Inlet Diameters

AP Diameter:

Oblique Diameter (Right & Left):

• Sacroiliac joint to contralateral iliopectineal eminence.

• Length: 12 cm.

Transverse Diameter: 

• 13 cm.

Cavity

Two important planes:

Midpelvis

• Area between plane of greatest and least pelvic dimensions.

Diameters

1. Transverse diameter /Interischial diameter/bispinous diameter

• 10 cm (Smallest in pelvis).

• Most important diameter for labor

2. Transverse / Bituberous diameter

• Distance between ischial tuberosities
• 11 cm.

3. AP diameter

• 13 cm.

Outlets

1. Anatomical Outlet

Anatomical Outlet Boundaries:

Boundary	Anatomical Landmark
Anterior	Lower pubic symphysis border
Lateral	Ischial tuberosity
Posterior	Coccyx tip

 

2. Obstetric Outlet

• Space between plane of least pelvic dimensions and anatomical outlet.

Conjugates

• Mnemonic: TOD
1. True Conjugate
2. Obstetric conjugate
3. Diagonal Conjugate

1. Diagonal conjugate

• Clinically measurable AP diameter of inlet

2. Obstetric conjugate

• Sacral promontory to mid pubic symphysis

• Diagonal conjugate − 1.5 cm

• Critical obstetric conjugate (OC)
• OC < 10 cm → vaginal delivery unlikely

Angle of Inclination: 

• Angle b/w inlet and horizontal

• 55°

Subpubic angle:

• Angle between descending pubic bone rami

• Male: Acute.

• Female: Obtuse.

Contracted Pelvis

Any major pelvic diameter decreased by 1 cm or if:

Management: 

• Always cesarean section.

Varieties of Contracted Pelvis

Naegele's Pelvis:

• Only one sacral bone ala is present.

• Mnemonic: Nagam oru ela kothi kondu poi

Robert Pelvis:

• Both sacral alae are absent.

• Robbed both ala

Caldwell Moloy Classification (PMQ)

Terminologies of Labour

Lie:

• Relationship of fetal long axis to uterus long axis.

• Correct dextrorotation

• 3 types
1. Longitudinal (m/c lie)
2. Transverse
3. Oblique

Presentation

1. Cephalic Presentation (most common)

2. Breech Presentation (m/c malpresentation)

3. Shoulder (m/c in Transverse )

Transverse Lie

• Presentation: Shoulder.

• Vaginal delivery: Not possible.

• Maximum risk of: Cord prolapse.

• If patient comes in antenatal period with transverse lie: ECV at ≥36 weeks.

• If patient comes in latent phase with transverse lie: ECV.
• If patient comes in active phase: C-section.
• Most common cause of transverse lie: Prematurity.
• Most common cause of transverse lie at term: Placenta previa.

Management of transverse lie:

• Antenatal period: 
• External cephalic version at 36 weeks.

• During labor: 
• C-section.

• Dead baby with transverse lie
• Neglected shoulder presentation: 
• C-section.

• Hand Prolapse in Transverse lie



• Presenting part: 
• Hand comes out.

• Management: 
• C-section.

Compound Presentation

• Presenting part: 
• Head and hand down.

• Management: 
• Vaginal delivery.

Presenting Part

• The portion of the fetus directly over the internal os (cervical opening)
• Palpable during a pelvic exam (P/V exam)

Attitude

• The relationship of fetal body parts to one another
• Normal attitude: Flexion

• Note: Face and brow presentations are due to abnormal fetal attitudes

• V-SOB → Sob with Flexed head - 9.5

• B-MV → Partially Extend head with BMW - 14

• F-SMV/SMB → Face smashed with completely extended
• SMV - 11.5
• SMB - 9.5

• Partially deflexed head / Incomplete flexion
• SOF → 10 cm
• Anterior fontanelle palpable
• Partially deflexed head in Sofa

Diameter of engagement

Face and Brow Presentation

• Cephalic

• In anencephaly, the face is the most common presenting part.

Position

• Definition: Relationship of denominator to maternal pelvis.
• Denominator: Bony point of reference in presenting part.
• Vertex: Occiput
• Face: Mentum
• Breech: Sacrum

• Most common position:

Stage	Common Position	Remarks
Before labor	LOA	Most common general fetal position
During labor (at engagement)	LOT	Most common occipito-anterior position during labor
After rotation (for delivery)	DOA	Final position before expulsion

Identifying Fetal Position (Occipitoposterior vs. Occipitoanterior)

• Occipitoposterior:
• Infraumbilical flattening.
• FHS heard in maternal flank area.

• Occipitoanterior:
• Smooth baby bump.
• FHS heard near umbilicus.

Occipito Posterior Position

• Most common Occipitoposterior position: ROP.

• Most common cause of OP position: Deflexed head.

• 2nd Most common cause of OP position: Android pelvis.

• Most common outcome in OP position: 
• Anatomically becomes DOA (Rotates 3/8th of circle).

• Best management of OP: Wait and watch.

Note: 

• Most common occipitoanterior position: LOA > ROA

• Most common position in breech: Left sacroanterior.

• Most common position in face: Left mentoanterior.

• Cord prolapse (max risk): Transverse lie.

Identification of Position

1. Identify occiput: Below posterior fontanelle (triangle shaped).

2. Occiput proximity:
• To pubic symphysis: OA.
• To sacral promontory: OP.
• Midway between them: OT.

3. Occiput direction:
• Towards your right: Mother's left.
• Towards your left: Mother's right.

Station

• Position of fetal head relative to ischial spine.

• Forceps: Applied at +2 or below.

Fetal skull

Breech

Malpresentation

• Most common cause: Prematurity.

• Most common cause of recurrent breech: Uterine malformation.

• Risk of gross congenital anomalies: 10%.

• IOCR (Induction of Cord Rupture): USG.

• Best Management: C-section at 39 weeks.

• Breech with head extended (Stargazer Breech): C-section.

• Risk of cord prolapse: Transverse > Footling > knee > flexed > frank.

• Vaginal Delivery, ECV C/I: Footling & Knee.

• Management in antenatal period: External cephalic version (ECV) ≥ 36 weeks.

• Vaginal Delivery in breech: Assisted breech delivery.

Types of Breech Presentation

• Complete/Flexed Breech:
• Hip & Knee Flexed
• Vaginal delivery possible

• Frank Breech:
• Hip Flexed, knee extended
• Vaginal delivery possible

• Footling Breech:
• Hip & knee extended
• C-section only

Criteria for Favorable Breech Delivery

• Gestational age: ≥36 weeks.

• Spontaneous onset of labor should be present.

• No H/O C-section (VBAC):
• Relative C/D.

• No C/I to vaginal delivery.

• Facility for emergency C-section should be present.

• USG should show:
• Frank breech > complete breech.
• Head should not be extended.
• Weight of baby: 2-4 kg.
• No anomaly causing abnormal labor.

Breech is not for vaginal delivery if

• Size >3.8kg

• Emergency CS and skilled Obstetrician not available

• Prior CS

• Contracted Pelvis

• Incomplete breach

• Oligohydramnios

• Severe IUGR

• Preterm

• Twin with 1st baby in breach

Manoeuvres for Breech Delivery

• Lovset's Maneuver:



• Delivery of shoulder.
• For extended arms
• Mnemonic: Lovers valakkum (rotate)
• Hold back of baby:
• & rotate.

Note

• Hart’s rule:
• During descent, part touching the levator ani rotates forward and medially

• Savage technique
• A warm towel is wrapped around lower part of baby
• Savage → save the cord
• Prevents directly touching cord → which may cause vasospasm and fetal distress

Delivery of Aftercoming Head in Breech

• Head is last part to be delivered.

• Most common cause of death in breech: intracranial hemorrhage.

• Head is born by movement of: Flexion.

Method of delivery in dorso anterior breech:

• Burn marshall technique

• Mauriceau smellie veit technique:
• malar flexion + shoulder traction

• Piper's Forceps: Long forceps

Dorsoposterior:

• Prague maneuver: Back is posterior

• Praying to mother

External Cephalic Version

Procedure

• Per-abdominally baby is rotated from transverse lie or breech and made cephalic.

• Done in OPD.

• Anesthesia not needed.

• Tocolytics are used to relax.

• In Rh negative females: Anti-D given after.

• No routine induction of labor after ECV.

• Should be done under continuous Fetal monitoring.

• Previous caesarean sections: Relative C/I.

Indication

• (not in knee or footling)

• Breech/Transverse lie in singleton pregnancy.

Prerequisites for ECV

• Period of gestation ≥36 weeks
• Done at 37 weeks: Less chances of reversion

• Liquor should be adequate and membranes should be intact.

• Can be done in early labor (Latent phase) if membranes are intact.

• Singleton pregnancy.

• Fetal heart rate should be normal on CTG.

• No contraindications for vaginal delivery.

Absolute Contraindications for ECV

• Oligohydramnios.

• Ruptured membranes.

• Active phase of labor.

• Twin/multifetal pregnancy.

• Abnormal fetal heart rate on CTG.

• Placenta previa/contracted pelvis.

• Uterus/fetus grossly anomalous.

Relative Contraindications for ECV 🗸🗸

• Heart disease in mother.

• IUGR + Oligohydramnios

• Macrosomia

• PIH / Preeclampsia

• Previous LSCS.

• Mnemonic: PIH

Classical Cesarean Section

• Incisions:
• In upper uterine segment: Classical cesarean section.
• In lower uterine segment: LSCS.

• Indications:
• Cancer cervix.
• Lower uterine segment adhered to bladder.
• Placenta previa + blood vessels all over lower segment.
• Lower segment not formed:
• Preterm cesarean section.
• Perimortem cesarean section (maternal cardiac arrest: Delivery in 4 mins).

• Previous Classical C-section:
• Never do vaginal delivery.
• LSCS (Next pregnancy) → To avoid uterine rupture.

• Note (Uterine Rupture):
• Bleeding during labour + pain abdomen.
• O/E → Uterus not felt, fetal parts superficially felt, loss of fetal station.

VBAC/TOLAC

• VBAC: Vaginal birth after cesarean.

• TOLAC: Trial of labour after cesarean.

ACOG Recommendation:

• TOLAC can be done in previous H/O LSCS (Any number).

• TOLAC can be done in previous Kronig incision (+/-).

• External cephalic version (ECV): Relative C/I in VBAC.

• Internal podalic version (IPV): Absolute C/I in VBAC.

• Twin in present pregnancy → Not a C/I except:
• Monochorionic monoamniotic twins
• Conjoint twins.
• 1st twin → Cephalic and 2nd twin → Transverse lie.

Monitoring in VBAC:

• Pulse rate of mother

• CTG monitoring.

• Uterine scar tenderness.