BACKGROUND AND PURPOSE:

• A previous study suggested that neonatal head circumference was more strongly associated with mode of delivery than birthweight
• Lipschuetz et al. (AJOG, 2018) assessed the association of prenatal head circumference measurement within 1 week of delivery and subsequent mode of delivery

METHODS:

• Multicenter restrospective electronic medical record-based study with data and birth outcomes extracted from the following patients
  • Primiparous women
  • Term singleton fetuses (37-42 weeks)
  • Presenting for ultrasound with fetal biometry within 1 week of delivery
• Fetal head circumference and estimated fetal weight (EFW) were cross-referenced with delivery ward files to obtain further information on
  • Maternal background
  • Obstetric history
  • Neonatal outcome parameters
• Biometry performed according to ISUOG guidelines
  • EFW was calculated using Hadlock formula
• Length of the second stage of labor
  • Prolonged: >3 hours with epidural anesthesia and 2 hours without
• Multinomial regression analysis provided adjusted odds ratio (OR) for instrumental delivery and unplanned cesarean delivery when the fetal head circumference was ≥35 cm or EFW ≥3900 g
  • Adjusted ORs were controlled for gestational age, fetal gender, and epidural anesthesia

RESULTS:

• 11,500 cases were collected
  • 906 elective cesarean deliveries were excluded
• FHC ≥35 cm and EFW ≥3900 g did not necessarily track together
  • Overall, only 1.8% had both findings and in those who had one increased finding, only 15.8% had both increased head circumference and EFW
• A fetal head circumference ≥35 cm increased the risk for unplanned cesarean delivery
• 32% of fetuses with fetal head circumference ≥35 cm were delivered by cesarean, vs 17% when fetal head circumference <35 cm
  • OR 2.49; 95% CI, 2.04–3.03
• When taking into account confounders, fetal head circumference ≥35 cm was associated with an increased risk of unplanned cesarean delivery
  • adjusted OR 1.75 (95% CI, 1.4–2.18)
• A fetal head circumference ≥35 cm increased the risk of instrumental delivery (OR 1.48; 95% CI, 1.16–1.88)
• The rate of prolonged second stage of labor was significantly increased from 22.7% in the total cohort to 31.0% when either the fetal head circumference was ≥35 cm or EFW ≥3900 g
• 5-minute Apgar score was ≤7 in 1.7% of cases where the fetal head circumference was ≥35 cm vs 0.6% when head circumference was <35 cm (P = .01)

CONCLUSION:

• Strength of this study is the cohort size
• Authors recognize limitation of retrospective design
• Fetal head circumference ≥35 cm (within 1 week of delivery) is an independent risk factor for unplanned cesarean delivery but not instrumental delivery
• Fetal head circumference ≥35 cm as well as EFW ≥3900 g was associated with increased risk of prolonged second stage of labor
• 35-cm cut-off was applicable to all gestational ages and may serve as an adjunct to EFW alone

Learn More – Primary Sources:

Sonographic large fetal head circumference and risk of cesarean delivery

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