Grand Rounds

Can Fetal Head Size Help Predict Risk of Cesarean Section?

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

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

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)

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

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