Active Phase Arrest

Active phase arrest is a failure of cervical dilatation in the active phase of labour: at 6 cm or more dilated with ruptured membranes, no cervical change for 4 hours or more despite adequate contractions, or for 6 hours or more with oxytocin and inadequate contractions. It results from inadequate uterine activity, malposition (occiput posterior or transverse), cephalopelvic disproportion or a large fetus. It matters because it is a leading reason for caesarean section, and finding the cause decides oxytocin or surgery.

• Risk factors: first pregnancy, obesity, large fetus, occiput posterior position, maternal short stature, induction, epidural.
• Adequate contractions are 3 to 5 in 10 minutes, lasting 40 to 60 seconds.
• Caesarean section is indicated when arrest persists after adequate oxytocin.

Women have strong contractions with no progress, becoming tired and distressed, and the partograph line stays flat. The cervix is thick, with marked caput or moulding in some.

• Partograph action line crossed.
• Marked caput and moulding of 2 plus or 3 plus suggest disproportion.
• Differential diagnosis: inadequate uterine activity, cephalopelvic disproportion, malposition (occiput posterior or transverse), abnormal fetal lie, cervical dystocia, chorioamnionitis.
• Complications: prolonged labour, exhaustion, chorioamnionitis, uterine rupture, obstructed labour, caesarean section, postpartum haemorrhage, fetal distress, fistula.

The approach is to confirm the arrest on the partograph and look for a cause.

• Digital cervical examination: dilatation, effacement, station, position, caput, moulding (degree 1 to 3); membrane status and liquor colour.
• Contraction count and duration; abdominal palpation for head level and lie; pelvic assessment.
• Cardiotocography; temperature, pulse, hydration, urine ketones; ultrasound for occiput position and fetal weight.
• Full blood count and C-reactive protein if fever; group and cross-match.

The principle is to correct inadequate contractions with amniotomy and oxytocin, and to deliver by caesarean section if the arrest persists or disproportion is present.

• Supportive: hydration (Ringer's lactate 1 litre IV over 2 hours); empty bladder; change position; one to one support; analgesia (epidural or pethidine 50 to 100 mg IM 4-hourly); continuous monitoring on oxytocin; stop oxytocin for tachysystole (more than 5 contractions in 10 minutes) or fetal distress.
• Pharmacological: oxytocin starting at 2 mU/minute and doubling every 30 minutes to a maximum of 32 mU/minute, aiming for 3 to 5 contractions in 10 minutes lasting 40 to 60 seconds, continued for 4 to 6 hours with a cervical examination every 2 to 4 hours; benzylpenicillin 5 million units IV then 2.5 million units 4-hourly in labour for group B streptococcus or rupture for 18 hours or more; ampicillin 2 g IV 6-hourly plus gentamicin 5 mg/kg IV once daily for chorioamnionitis, with metronidazole 500 mg IV 8-hourly added after caesarean section; cefazolin 2 g IV before caesarean section; oxytocin 10 IU IM at birth then infusion of 20 IU in 1 litre sodium chloride 0.9 percent at 125 mL per hour for 4 hours.
• Procedures: amniotomy if membranes are intact; caesarean section for no cervical change after 4 to 6 hours of adequate oxytocin, for cephalopelvic disproportion, or for fetal compromise; no oxytocin when disproportion is clear (marked moulding, high head, caput).
• Special groups: women with a previous caesarean section have oxytocin with senior review and continuous monitoring because of the risk of uterine rupture; grand multiparas avoid oxytocin unless closely monitored; chorioamnionitis needs delivery whatever the dilatation.
• Red flags: tachysystole, fetal heart rate abnormality, fever above 38 degrees Celsius, scar pain or tenderness, bandl ring, bleeding, maternal exhaustion.
• Follow-up: cervical examination every 2 to 4 hours on oxytocin; maternal temperature 4-hourly; postnatal review for perineal and bladder function; counselling on mode of birth in the next pregnancy.