Hypotonic Uterine Dysfunction

Hypotonic uterine dysfunction is weak, infrequent or short uterine contractions (fewer than 3 in 10 minutes, each shorter than 40 seconds, easily indented by a finger at the peak), which fail to dilate the cervix. It is the commonest pattern of dysfunctional labour and usually appears in the active phase.

Causes are overdistension (twins, polyhydramnios, large baby), grand multiparity, exhaustion, dehydration, sedation or epidural, and malposition.

It matters because it is treatable with oxytocin, but disproportion must be excluded and it raises the risk of postpartum haemorrhage.

• Risk factors: first labour, grand multiparity, twin pregnancy, polyhydramnios, macrosomia, early epidural, sedation, chorioamnionitis.
• Uterine tone is low between and during contractions.
• Response to oxytocin is usually good.

Women have mild painless or only slightly painful contractions that are infrequent, with slow cervical change and a uterus that is easily indented at the peak of a contraction. They may be tired and dehydrated.

• Fewer than 3 contractions in 10 minutes.
• Slow cervical dilatation of less than 1 cm per hour.
• Differential diagnosis: false labour, latent phase, hypertonic dysfunction, malposition, cephalopelvic disproportion, chorioamnionitis, epidural effect.
• Complications: prolonged labour, exhaustion, chorioamnionitis, fetal distress, atonic postpartum haemorrhage, caesarean section, uterine rupture with unsafe oxytocin.

The diagnosis is by palpation and tocography with exclusion of obstruction.

• Contractions palpated for 10 minutes: count, duration and strength; tocography where available (peak pressure below 25 mmHg is weak).
• Cervical dilatation, station, position, caput and moulding; bony pelvis.
• Cardiotocography; temperature, pulse, hydration, ketones.
• Ultrasound for position, estimated fetal weight, liquor volume and twin presentation.

The principle is to exclude disproportion, rupture the membranes and give oxytocin to restore effective contractions.

• Supportive: Ringer's lactate 1 litre IV over 1 to 2 hours; empty the bladder; walking and upright positions; one to one support; analgesia; continuous cardiotocography on oxytocin.
• 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), aiming for 3 to 5 contractions in 10 minutes lasting 40 to 60 seconds, stopped for tachysystole or fetal distress; 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; oxytocin 10 IU IM after birth, then 20 IU in 1 litre at 125 mL per hour for 4 hours; misoprostol 800 micrograms sublingual and tranexamic acid 1 g IV over 10 minutes for postpartum haemorrhage from atony; carboprost 250 micrograms IM every 15 minutes (maximum 8 doses) if atony persists (not in asthma); cefazolin 2 g IV before caesarean section.
• Procedures: amniotomy when the head is engaged and membranes are intact; uterine massage and bimanual compression for atony; balloon tamponade or compression sutures for refractory bleeding; caesarean section for no progress after 4 hours of adequate oxytocin, disproportion or fetal compromise.
• Special groups: grand multiparity and a uterine scar use oxytocin with lower starting rates and senior review because of uterine rupture; twins and polyhydramnios have oxytocin ready for the third stage.
• Red flags: tachysystole, abnormal fetal heart rate, scar pain, fever above 38 degrees Celsius, bleeding, uterus soft after birth.
• Follow-up: cervical examination every 2 to 4 hours; observe for bleeding for 2 hours after birth then 4-hourly for 24 hours; haemoglobin at 24 hours and iron: ferrous sulphate 200 mg oral 8-hourly for 3 months if anaemic.