Deep Transverse Arrest (DTA)

Definition

• The occiput lies on one side of the pelvis, the sinciput on the other
• The head is badly flexed (deflexed)
• It is diagnosed only during the 2nd stage of labour
• If firmly fixed, obstructed labour will result

Note: This is distinct from persistent occipito-posterior (OP) where the head descends in the posterior position.

Mechanism / Pathophysiology

Etiology

1. Android pelvis - the most important cause; the forward-projecting ischial spines and narrow mid-pelvis prevent rotation
2. Epidural analgesia - reduces tone of pelvic floor muscles that normally guide fetal rotation
3. Uterine inertia (weak contractions) - insufficient driving force to complete rotation

• Platypelloid pelvis (flat pelvis)
• Cephalopelvic disproportion (CPD)
• Fetal macrosomia
• Relative deflexion of the head (occiput fails to lead)

Diagnosis

Clinical features:

• Labour prolonged - especially 2nd stage
• Head at or below ischial spines, not descending

Vaginal examination:

• Sagittal suture felt in the transverse bispinous diameter
• Head at or below ischial spines (station 0 or lower)
• Both fontanelles at the same level (transverse plane)
• Anterior fontanelle palpable on one side, posterior fontanelle on the other (sinciput and occiput at same level - poorly flexed)
• Any pelvic abnormality (android, platypelloid) noted on examination
• Head may show caput and moulding

ICD code: 660.3 - Obstructed labour caused by deep transverse arrest and persistent occipito-posterior position

Management

Algorithm based on pelvic adequacy:

DTA Diagnosed
    |
    ├─── Pelvis ADEQUATE ──────────────────────────────┐
    │                                                  │
    │   Best option: Ventouse (vacuum extraction)      │
    │   (Ideal in all cases - AIPGME/DNB key fact)     │
    │                                                  │
    │   Alternatives:                                  │
    │   • Manual rotation → outlet forceps             │
    │   • Kielland's forceps rotation + extraction     │
    │                                                  │
    └─── Pelvis INADEQUATE ────────────────────────────┤
         (midpelvic contraction, CPD)                  │
              → Caesarean section                      │
                                                       │
    ── DEAD FETUS ─────────────────────────────────────┘
              → Craniotomy (destructive operation)

1. Ventouse (Vacuum Extraction) - Preferred method

• Ideal in all cases with adequate pelvis and non-rotation due to weak contractions or poor pelvic floor tone
• The cup is placed over the flexion point (3 cm anterior to the posterior fontanelle on the sagittal suture)
• Traction encourages autorotation as the head descends
• Advantage: Less traumatic than forceps; allows natural rotation

2. Manual Rotation

• Full hand (whole hand) method - Four fingers placed behind the occiput, thumb on anterior parietal bone; rotate to OA
• Half-hand (Schatz manoeuvre) - Two fingers used to dislodge and rotate the head

• Cord prolapse (head may be dislodged)
• Displacement of head upward
• Cervical or vaginal lacerations

3. Kielland's Forceps - Rotational Forceps

• Minimal pelvic curve (almost straight)
• A sliding lock that allows asynclitism
• Can be applied in asynclitic heads

• Direct application (inversion/wandering method)
• Classical application (direct application blade by blade)

• No chance of head displacement
• No accidental cord prolapse
• Rotation can be done above or below the level of obstruction
• More controlled

• Requires skilled operator
• Risk of maternal soft tissue injury
• Risk of fetal injury if used incorrectly

4. Caesarean Section

• Pelvis is inadequate (midpelvic contraction, android pelvis with no vaginal delivery possible)
• Failed instrumental delivery
• Fetal distress
• Modern obstetrics trend: CS is the procedure of choice in most centres when instrumental rotation is not feasible

5. Craniotomy

• Only for dead fetus when vaginal delivery is attempted
• Rarely performed today

Comparison with Related Conditions

Key Exam Points (MCQ-Important)

1. DTA is diagnosed only in the 2nd stage of labour
2. Most common cause: Android pelvis + Epidural analgesia + Uterine inertia
3. Best mode of delivery with adequate pelvis: Ventouse (vacuum extraction)
4. Rotational forceps used: Kielland's forceps
5. Kielland's advantage over manual rotation: no cord prolapse, no head displacement
6. Inadequate pelvis: Caesarean section
7. Dead fetus: Craniotomy
8. DTA is associated with obstructed labour if untreated
9. Face-to-pubis delivery (direct OP) - most common complication: complete perineal tear
10. Spontaneous delivery in persistent OP: 70% rotate to OA in 2nd stage; 10% deliver face-to-pubis; 20% need intervention