Cephalopelvic Disproportion

Cephalopelvic disproportion is a mismatch between the size of the fetal head and the maternal pelvis, so that the head cannot pass through the pelvis despite adequate contractions. It results from a small or deformed pelvis (rickets, fractures, malnutrition in childhood, adolescence), a large baby, a hydrocephalic head or malposition. It matters because it leads to obstructed labour, uterine rupture, fistula and fetal death unless recognised and managed by caesarean section.

• Risk factors: short stature below 150 cm, adolescent mother, childhood malnutrition, rickets, pelvic or spinal injury, birth weight above 4000 g, diabetes, post term pregnancy.
• True disproportion is uncommon, but relative disproportion from malposition is common.
• Shoe size and height are poor predictors on their own.

Women have a head that stays high or unengaged in late pregnancy or labour, slow progress despite strong contractions, marked caput and moulding, and an oedematous cervix. Late features are exhaustion, fever and signs of obstruction.

• Head more than 3 fifths palpable above the pelvic brim in labour.
• Moulding of 3 plus with overlapping sutures that do not reduce.
• Differential diagnosis: inadequate uterine activity, malposition, abnormal lie, cervical dystocia, hydrocephalus, pelvic tumour, obstructed labour.
• Complications: obstructed labour, uterine rupture, obstetric fistula, chorioamnionitis, fetal hypoxia, birth injury, caesarean section, postpartum haemorrhage, maternal and fetal death.

The diagnosis is made by clinical assessment of the head and pelvis, and by the course of labour.

• Abdominal palpation: fifths of head above the brim; vaginal examination: sacral promontory reachable, narrow subpubic angle (below 90 degrees), ischial spines prominent, interspinous distance below 10 cm, diagonal conjugate below 11.5 cm.
• Partograph with slow progress, caput and moulding of 2 plus or 3 plus, hot dry vagina and oedematous cervix in obstruction.
• Ultrasound for estimated fetal weight, biparietal diameter and hydrocephalus; pelvic X-ray or MRI pelvimetry only when it would change management.
• Maternal pulse, temperature, hydration and urine output.

The principle is delivery by caesarean section when disproportion is clear, with labour allowed only in borderline cases under close observation.

• Supportive: Ringer's lactate 1 litre IV over 1 hour for dehydration; empty the bladder by catheter; stop oxytocin; continuous cardiotocography; group and cross-match; antibiotics before delivery in prolonged labour.
• Pharmacological: cefazolin 2 g IV as a single dose before caesarean section (3 g above 120 kg); ampicillin 2 g IV 6-hourly plus gentamicin 5 mg/kg IV once daily plus metronidazole 500 mg IV 8-hourly for suspected infection, continued until afebrile for 48 hours; oxytocin 10 IU IM after birth, 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); newborn vitamin K 1 mg IM.
• Procedures: caesarean section for confirmed disproportion, with senior surgeon when the head is deep in the pelvis; labour allowed with 2-hourly review in borderline cases (head engaging, moulding 1 plus) with no oxytocin when disproportion is likely; symphysiotomy only by trained operators with a live fetus and a head that is not high; bladder catheter for 7 to 14 days after obstructed labour.
• Special groups: adolescents and women of short stature below 150 cm have a low threshold for caesarean section; women with a previous caesarean section and disproportion do not have labour augmented; HIV positive women continue tenofovir 300 mg, lamivudine 300 mg and dolutegravir 50 mg oral once daily.
• Red flags: hot dry vagina, bandl ring, blood-stained urine, maternal pulse above 120 per minute, fever above 38 degrees Celsius, absent fetal movements, abnormal fetal heart rate.
• Follow-up: bladder checks for leaking urine; review at 6 weeks; counselling that future births will be by planned caesarean section.