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Objective To examine the relationship between the cervical dilatation at which women present in labour and the subsequent likelihood of caesarean section.

Design Retrospective cohort study.

Setting University teaching hospital.

Population 3220 women met the entry criteria from 14,050 deliveries between January 1995 and December 1999.

Methods Women meeting the following criteria were identified: those in spontaneous labour with a singleton pregnancy and a cephalic presentation at 37–42 weeks of gestation; all women delivering within 36 hours of first presentation were included. Women who had spontaneous rupture of the membranes before first attendance were excluded.

Main outcome measures The primary outcome was the rate of caesarean section. Secondary outcomes were operative vaginal delivery, fetal weight, cord pH, five minute Apgar score, length of labour, labour augmentation with oxytocin and epidural analgesia.

Results The risk of caesarean section decreased with increasing cervical dilatation at presentation. This was true for nulliparous (n=1168) and parous women (n=2052). The caesarean section rate of nulliparous women presenting at 0–3cm (n=812) was 10.3%, compared with 4.2% for those presenting at 4cm–10cm (n=356), and the mean duration of labour before presentation was 2.0 hours versus 4.5 hours, respectively (P=0.0001). For parous women the caesarean section rates were 5.7% and 1.3%, respectively (P=0.0001). There were significantly greater frequencies of use of oxytocin and epidural analgesia by women presenting earlier in labour. The caesarean section rate of 185 nulliparae (15.8%) who were initially allowed home was no different from those admitted immediately (9.2%vs 8.2%, P=0.67). Similarly, 196 (9.5%) of multiparae went home and had a caesarean section rate of 3.6%, compared with 3.1% if admitted immediately (P=0.76).

Conclusions Women who present to hospital at 0–3cm spend less time in labour before presentation and are more likely to have obstetric intervention than those presenting in more advanced labour. Outcomes were similar whether or not the woman was initially allowed home.