There is global concern about rising caesarean section rates. Identification of risk factors could lead to preventative measures.

To describe the association between neonatal head circumference and (i) caesarean section for failure to progress, (ii) intrapartum caesarean section overall.

Materials and Methods
This was a retrospective cohort study of 11 687 singleton live births with cephalic presentation, attempted vaginal birth and at least 37 completed weeks gestation from January 2005 to June 2009. Neonatal head circumference was grouped into quartiles and multiple logistic regressions performed.

The rates of caesarean section for failure to progress were 4.1, 6.4, 8.8 and 14.3% in successive head circumference quartiles. Rates of intrapartum caesarean section overall were 8.7, 12.1, 15.8 and 21.5%. The odds ratios for caesarean section for failure to progress were: 1.00, 1.33 (95% CI 1.02‐ 1.73), 1.54 (1.18–2.02) and 1.93 (1.44–2.57) for successive head circumference quartiles after adjusting for multiple demographic and clinical factors. The adjusted odds ratios for intrapartum caesarean section for any indication were: 1.00, 1.52 (95% CI 1.24–1.87), 1.99 (1.62–2.46) and 2.38 (1.89–3.00), respectively.

There is a strong positive relationship between head circumference quartile and both caesarean section for failure to progress and caesarean for any indication. If this finding is confirmed using ultrasound measurements, there is potential for head circumference to be incorporated into predictive models for intrapartum caesarean section with a view to offering interventions to reduce the risk of caesarean section.