Sonographic large fetal head circumference and risk of cesarean delivery

Persistently high rates of cesarean deliveries are cause for concern for physicians, patients, and health systems. Prelabor assessment might be refined by identifying factors that help predict an individual patient's risk of cesarean delivery. Such factors may contribute to patient safety and satisfaction as well as health system planning and resource allocation. In an earlier study, neonatal head circumference was shown to be more strongly associated with delivery mode and other outcome measures than neonatal birthweight.

In the present study we aimed to evaluate the association of sonographically measured fetal head circumference measured within 1 week of delivery with delivery mode.

This was a multicenter electronic medical record-based study of birth outcomes of primiparous women with term (37-42 weeks) singleton fetuses presenting for ultrasound with fetal biometry within 1 week of delivery. Fetal head circumference and estimated fetal weight were correlated with maternal background, obstetric, and neonatal outcome parameters. Elective cesarean deliveries were excluded. Multinomial regression analysis provided adjusted odds ratios for instrumental delivery and unplanned cesarean delivery when the fetal head circumference was ≥35 cm or estimated fetal weight ≥3900 g, while controlling for possible confounders.

In all, 11,500 cases were collected; 906 elective cesarean deliveries were excluded. A fetal head circumference ≥35 cm increased the risk for unplanned cesarean delivery: 174 fetuses with fetal head circumference ≥35 cm (32%) were delivered by cesarean, vs 1712 (17%) when fetal head circumference <35 cm (odds ratio, 2.49; 95% confidence interval, 2.04-3.03). A fetal head circumference ≥35 cm increased the risk of instrumental delivery (odds ratio, 1.48; 95% confidence interval, 1.16-1.88), while estimated fetal weight ≥3900 g tended to reduce it (nonsignificant). Multinomial regression analysis showed that fetal head circumference ≥35 cm increased the risk of unplanned cesarean delivery by an adjusted odds ratio of 1.75 (95% confidence interval, 1.4-2.18) controlling for gestational age, fetal gender, and epidural anesthesia. The rate of prolonged second stage of labor was significantly increased when either the fetal head circumference was ≥35 cm or the estimated fetal weight ≥3900 g, from 22.7% in the total cohort to 31.0%. A fetal head circumference ≥35 cm was associated with a higher rate of 5-minute Apgar score ≤7: 9 (1.7%) vs 63 (0.6%) of infants with fetal head circumference <35 cm (P = .01). The rate among fetuses with an estimated fetal weight ≥3900 g was not significantly increased. The rate of admission to the neonatal intensive care unit did not differ among the groups.

Sonographic fetal head circumference ≥35 cm, measured within 1 week of delivery, is an independent risk factor for unplanned cesarean delivery but not instrumental delivery. Both fetal head circumference ≥35 cm and estimated fetal weight ≥3900 g significantly increased the risk of a prolonged second stage of labor. Fetal head circumference measurement in the last days before delivery may be an important adjunct to estimated fetal weight in labor management.