A 28-year-old primigravida at term presents to the labour ward in active labour. On examination, the cervix is 6 cm dilated, 80% effaced, and contractions are occurring every 3 minutes lasting 45 seconds. Which is the most common cause of prolonged labour in the first stage in this patient?

Explanation

## Causes of Prolonged First Stage of Labour **Key Point:** Inadequate uterine contractions (hypotonic or incoordinate contractions) account for approximately 50–70% of cases of prolonged first stage of labour, making it the single most common cause. ### Frequency of Causes | Cause | Frequency | Mechanism | |-------|-----------|----------| | **Inadequate uterine contractions** | 50–70% | Hypotonic or incoordinate contractions; weak intensity or irregular pattern | | Cephalopelvic disproportion | 15–20% | Mechanical obstruction; requires pelvimetry and fetal assessment | | Fetal malposition | 10–15% | ODP, transverse lie, or deflexed head; may self-correct | | Maternal exhaustion | 5–10% | Secondary to prolonged labour; not a primary cause | ### Clinical Features of Inadequate Contractions - **Hypotonic contractions:** Low amplitude (<20 mmHg), widely spaced, brief duration - **Incoordinate contractions:** Uncoordinated uterine activity without normal fundal dominance - **Slow cervical dilation:** Typically <1 cm/hour in primigravida - **Maternal factors:** Maternal obesity, multiparity (uterine laxity), sedation, epidural analgesia **High-Yield:** In a primigravida with normal pelvimetry and well-flexed fetal head, inadequate contractions should be suspected first. Management involves augmentation with oxytocin infusion. **Clinical Pearl:** Maternal exhaustion is a *consequence* of prolonged labour, not a primary cause. It develops secondary to inadequate contractions or obstruction. ### Differential Diagnosis in First Stage Prolongation ```mermaid flowchart TD A[Prolonged First Stage]:::outcome --> B{Contraction Pattern?}:::decision B -->|Inadequate/Hypotonic| C[Inadequate Uterine Contractions]:::outcome B -->|Normal| D{Pelvimetry & Fetal Position?}:::decision D -->|Abnormal pelvis| E[Cephalopelvic Disproportion]:::urgent D -->|Malposition| F[Fetal Malposition]:::outcome D -->|Normal| G[Reassess; Consider Incoordinate Contractions]:::action ``` [cite:Williams Obstetrics 26e Ch 21]