Evidence Library · Reasons for cesarean

Suspected big baby

Among the weakest reasons for a cesarean, and one of the most common.

Two things have to be true for "the baby is too big" to justify surgery: the estimate has to be accurate, and acting on it has to help. Neither is well supported.

A decision analysis found that to prevent one permanent nerve injury to the baby's arm, you would need to perform 2,345 cesareans in non-diabetic women using a 4,000 gram threshold, or 3,695 cesareans using a 4,500 gram threshold.

2,345

Cesareans to prevent one permanent arm nerve injury, 4,000 g threshold

Decision analysis

3,695

Cesareans to prevent one, 4,500 g threshold

Decision analysis

The estimates themselves are also imprecise. In a review of 41 studies and 112,034 patients, an estimated weight above 4,000 grams correctly identified more than half of the babies who did turn out to be large. It performed far worse at predicting shoulder dystocia, correctly flagging only 22% of the cases that happened.

Where this comes from:

284. Rouse DJ, Owen J, Goldenberg RL, Cliver SP. The effectiveness and costs of elective cesarean delivery for fetal macrosomia diagnosed by ultrasound. JAMA. 1996;276(18):1480-1486.

270. Moraitis AA, Shreeve N, Sovio U, Brocklehurst P, Heazell AEP, Thornton JG, et al. Universal third-trimester ultrasonic screening using fetal macrosomia in the prediction of adverse perinatal outcome: a systematic review and meta-analysis of diagnostic test accuracy. PLoS Med. 2020;17(10):e1003190.

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