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Grand Rounds

Can Fetal Head Size Help Predict Risk of Cesarean Section?

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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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Related ObG Topics:

Can Abdominal Circumference Alone Be Used to Predict SGA or LGA Newborns?
Can C-Section risk be Predicted in Nulliparous Women?

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