Arrest of Descent

Arrest of descent is failure of the fetal head to move down the birth canal in the second stage of labour, despite full cervical dilatation, adequate contractions and maternal pushing. Causes are weak expulsive effort (exhaustion, dense epidural), malposition (occiput posterior or transverse), cephalopelvic disproportion, a large fetus and rigid soft tissues. It matters because delay leads to fetal hypoxia, birth injury, severe perineal tears, postpartum haemorrhage, sepsis and obstetric fistula.

• Definition: no descent after 3 hours of pushing in a first labour (4 hours with epidural) or 2 hours in a later labour (3 hours with epidural), or when the head stays at one station for 1 hour.
• Risk factors: first labour, obesity, birth weight above 4000 g, occiput posterior position, epidural, short stature, prolonged first stage.
• Early assessment of position and station decides between assisted delivery and caesarean section.

Women push with each contraction without the head advancing, become tired and distressed, and the head stays at one level on repeated examination. The perineum does not bulge and the scalp is not visible at the vulva.

• Head at station 0 to +2 with caput and moulding of 2 plus or 3 plus.
• Maternal pulse above 100 per minute and ketosis in long labours.
• Differential diagnosis: inadequate expulsive effort, occiput posterior or transverse position, cephalopelvic disproportion, large fetus, rigid perineum, full bladder, chorioamnionitis, uterine rupture.
• Complications: fetal hypoxia and acidosis, birth injury, third and fourth degree tears, postpartum haemorrhage, chorioamnionitis, shoulder dystocia, uterine rupture, obstetric fistula, caesarean section.

The diagnosis is made by abdominal and vaginal examination at full dilatation, repeated at intervals, with a record of the second stage on the partograph.

• Abdominal palpation: fifths of the head palpable above the pelvic brim (2 fifths or less means engaged).
• Vaginal examination: full dilatation, station relative to the ischial spines, position (direction of the sagittal suture), caput, moulding, liquor colour, sacral curve, ischial spines and subpubic angle.
• Cardiotocography; maternal pulse, temperature, urine output and ketones.
• Ultrasound for occiput position and estimated fetal weight where available.

The principle is to correct reversible causes, assist delivery when the head is low, and operate when the head is high or disproportion is present.

• Supportive: change position (squatting, kneeling, hands and knees, side lying); empty the bladder by catheter; Ringer's lactate 1 litre IV over 1 hour for dehydration; rest for 30 to 60 minutes with a dense epidural when fetal heart rate is normal; one to one support; continuous cardiotocography; call senior help.
• 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), only when contractions are weak and there is no disproportion; lignocaine 1 percent 10 to 20 mL (maximum 3 mg/kg, not above 200 mg) for perineal infiltration, or 10 mL each side for pudendal block; amoxicillin-clavulanate 1.2 g IV as a single dose after operative vaginal delivery; cefazolin 2 g IV as a single dose before caesarean section; oxytocin 10 IU IM after birth of the baby, then 20 IU in 1 litre Ringer's lactate at 125 mL per hour for 4 hours; tranexamic acid 1 g IV over 10 minutes if bleeding exceeds 500 mL; paracetamol 1 g oral 6-hourly (maximum 4 g in 24 hours) after birth.
• Procedures: vacuum or forceps when the head is engaged and at station +2 or lower with no disproportion (vacuum: up to 3 pulls, 2 detachments and 20 minutes in total; forceps: up to 3 pulls); episiotomy when needed; caesarean section when the head is higher than +2, with disproportion, after failed assisted delivery or with fetal compromise, with the deep head disimpacted by an assistant's hand in the vagina or by reverse breech extraction; symphysiotomy only by trained operators with a live fetus and a head that is not high.
• Special groups: a uterine scar uses oxytocin only with continuous monitoring and senior review because of uterine rupture; HIV positive women continue tenofovir 300 mg, lamivudine 300 mg and dolutegravir 50 mg oral once daily and avoid scalp electrodes and fetal scalp sampling.
• Red flags: fetal heart rate below 110 or above 160 beats per minute, thick meconium, fever above 38 degrees Celsius, scar pain, bleeding, bandl ring, maternal pulse above 120 per minute.
• Follow-up: bladder catheter for 24 hours after assisted delivery and for 7 to 14 days after obstructed labour; check perineum and bladder function before discharge; review at 1 week and 6 weeks; plan the next birth with the surgical findings.