Deep Transverse Arrest

Deep transverse arrest is arrest of the fetal head in the occiput transverse position at the level of the ischial spines (station 0 to +2) with full dilatation, because the head fails to rotate to occiput anterior. It is caused by a flat or android pelvis, a deflexed head, weak contractions, epidural analgesia and a large head. It matters because the head is wedged in the mid pelvis, so delivery needs rotation by experienced hands, and unskilled traction causes severe fetal and maternal injury.

• Risk factors: first labour, epidural, flat pelvis (platypelloid) or android pelvis, large baby, deflexed head, prolonged second stage.
• It is a form of arrest of descent at the mid pelvis.
• Senior help is needed early.

Women have full dilatation with a head that has not descended or rotated after prolonged pushing, with tiredness and often an epidural in place. The sagittal suture lies in the transverse diameter of the pelvis.

• Sagittal suture transverse, head at station 0 to +2.
• Marked caput and moulding.
• Differential diagnosis: cephalopelvic disproportion, occiput posterior position, inadequate pushing, arrest of descent from other cause, asynclitism, uterine rupture.
• Complications: prolonged second stage, fetal acidosis, failed assisted delivery, caesarean section at full dilatation, third and fourth degree tears, shoulder dystocia, postpartum haemorrhage, birth injury.

The diagnosis is made by vaginal examination at full dilatation with confirmation of the position.

• Vaginal examination: full dilatation, sagittal suture in the transverse diameter, posterior fontanelle to one side, ears felt (confirm by ear position), station 0 to +2, caput, moulding.
• Abdominal palpation: head still partly palpable above the pelvic brim (1 fifth to 2 fifths).
• Ultrasound for occiput position and estimated fetal weight where available.
• Cardiotocography; maternal pulse, temperature and urine output; assessment of the bony pelvis.

The principle is to confirm there is no disproportion, give time and oxytocin for weak contractions, and rotate by hand, forceps or vacuum, or operate.

• Supportive: hydration (Ringer's lactate 1 litre IV over 1 hour); empty the bladder; hands and knees or lateral position for 30 minutes; delayed pushing with a dense epidural; continuous cardiotocography; senior obstetrician in theatre; consent for caesarean section.
• Pharmacological: oxytocin 10 IU in 1 litre Ringer's lactate (10 mU/mL) started at 12 mL per hour (2 mU/minute) and doubled every 30 minutes to a maximum of 192 mL per hour (32 mU/minute) for weak contractions without disproportion; lignocaine 1 percent 10 mL each side for pudendal block, and 10 to 20 mL (maximum 3 mg/kg, not above 200 mg) for perineal infiltration; amoxicillin-clavulanate 1.2 g IV as a single dose after operative vaginal delivery; cefazolin 2 g IV before caesarean section; oxytocin 10 IU IM after birth, then 20 IU in 1 litre at 125 mL per hour for 4 hours; tranexamic acid 1 g IV over 10 minutes if bleeding exceeds 500 mL.
• Procedures: manual rotation to occiput anterior with a hand in the vagina (flex the head, rotate with the contraction) followed by forceps or vacuum; rotational forceps (Kielland) or vacuum with rotation by an experienced operator only; caesarean section for failed rotation, a high head, disproportion or fetal compromise (with an assistant pushing the head up from below or reverse breech extraction when the head is deep).
• Special groups: a uterine scar uses oxytocin only with senior review; epidural analgesia allows an extra hour for descent.
• Red flags: abnormal fetal heart rate, thick meconium, scar tenderness, fever above 38 degrees Celsius, bleeding, maternal exhaustion.
• Follow-up: bladder catheter for 24 hours after assisted birth; check perineum for sphincter injury; observe for bleeding for 24 hours; review at 6 weeks; counselling on the next birth.