Open Access Research article

Fetal head circumference, operative delivery, and fetal outcomes: a multi-ethnic population-based cohort study

Andrew Mujugira13*, Alfred Osoti1, Ruth Deya1, Stephen E Hawes1 and Amanda I Phipps12

Author Affiliations

1 Department of Epidemiology, University of Washington, Seattle, WA, USA

2 Fred Hutchinson Cancer Research Center, Seattle, WA, USA

3 International Clinical Research Center, Department of Global Health, University of Washington, 325 Ninth Avenue, Box 359927, Seattle, WA, 98104, USA

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BMC Pregnancy and Childbirth 2013, 13:106  doi:10.1186/1471-2393-13-106

Published: 7 May 2013



Operative delivery procedures, such as primary cesarean section, vacuum-assisted, and forceps-assisted vaginal delivery increase maternal and fetal morbidity, and the cost of care. We evaluated whether large fetal head circumference (FHC) independently increases risk of such interventions, as well as fetal distress or low Apgar score, in anatomically normal infants.


We conducted a population-based retrospective cohort study using Washington State birth certificate data. We included singleton, term infants born to nulliparous mothers from 2003ā€“2009. We compared mode of delivery and fetal outcomes in 10,750 large-FHC (37-41 cm) infants relative to 10,750 average-FHC (34 cm) infants, frequency matched by birth-year.


Large-FHC infants were nearly twice as likely to be delivered by primary cesarean section as average-FHC infants (unadjusted relative risk [RR] 1.84, 95% confidence interval [CI]: 1.77, 1.92). The RR for primary cesarean section associated with large-FHC was largest for mothers aged 19 years or less (RR 2.28; 95% CI: 1.99, 2.61), and smallest for mothers aged 35 years or greater (RR 1.51; 95% CI: 1.37, 1.66) [test of homogeneity, pā€‰<ā€‰0.001]. Large-FHC infants were at increased risk of vacuum-assisted vaginal delivery (RR 1.55; 95% CI: 1.43, 1.69), and forceps-assisted vaginal delivery (RR 1.61; 95% CI: 1.32, 1.97). There was no difference in risk of fetal distress (RR 0.97; 95% CI: 0.89, 1.07) for large-FHC versus average-FHC infants. Risk estimates were unaffected by adjustment for potential confounders.


Nulliparous mothers of large-FHC infants are at increased risk of primary cesarean section, vacuum-assisted and forceps-assisted vaginal delivery relative to mothers of average-FHC infants. Maternal age modifies the association between FHC and primary cesarean section.

Fetal head circumference; Cesarean section; Operative delivery; Fetal distress; Low Apgar score