Ultrasound assessment of fetal head circumference at the onset of labor as a predictor of operative delivery

Abstract

Objective: This study sought to determine whether ultrasound assessment of fetal head circumference (FHC) at the onset of labor can predict the likelihood of operative delivery.

Methods: We performed a prospective cohort study of 200 nulliparous women with singleton, cephalic, term pregnancies in an Irish Maternity Hospital. Transabdominal ultrasound assessment of FHC was performed when spontaneous labor was diagnosed or immediately prior to induction. Odds ratios for operative delivery (instrumental delivery or cesarean section) and maternal and neonatal morbidity were calculated using logistic regression with FHC categorized at a ≥350-mm cut-off (90th percentile).

Results: Ultrasound assessment of FHC at the onset of labor was highly correlated with post-delivery neonatal head circumference (NHC) (Pearson's correlation coefficient 0.74), suggesting that it can be measured reliably. FHC ≥350 mm was associated with more than twice the risk of any operative delivery (OR 2.5, 95% CI 1.0-6.2) and a two-fold increased risk of cesarean section for dystocia (OR 2.0, 95% CI 1.0-4.3). Differences in maternal and neonatal morbidity were not statistically significant.

Conclusion: These preliminary data suggest that ultrasound assessment of FHC at the onset of labor may be useful in identifying women at greater risk of intrapartum intervention and warrant further research.

Keywords: Cesarean section; fetal head circumference; instrumental delivery; labor; ultrasound.