Table 1.

Estimated number of permanent BPI prevented by routine CS for fetuses greater than 4,500 grams

Assumptions
1. 100,000 births
2. 13,000 BW 4,000–4,500 g; 15% CS in labor
3. 2,000 BW >4,500 g; 30% CS in labor
4. 5% SD in 4,000–4,500 g group
10% SD in >4,500 g group
5. 10% BPI with SD
6. 20% of BPI are permanent
7. US will identify all babies >4,500 g
US will falsely identify 20% (N=2,600) of 4,000–4,500 g group as >4,500 g
4,000–4,500 g		.4,500 g
13,000		2,000
↓	2,000 CS in labor	↓	600 CS in labor
11,000 vag del		1,400 vag del
↓		↓
550 SD		140 SD
↓		↓
55 BPI		14 BPI
↓		↓
11 perm BPI		3 perm BPI

Notes: Policy of routine CS if >4,500 g results in 2,000+2,600=4,600 CS. Of these, 600+(15% of 2,600)=1,000 would have had a CS in labor. Therefore: 3,600 extra CS. Would have prevented 3 BPI in >4,500 g and 3 BPI in the 2,600 women in 4,000–4,500 g group who avoided attempted vaginal delivery.

Abbreviations: BPI, brachial plexus injury; BW, birth weight; CS, caesarean section; Perm, permanent; SD, shoulder dystocia.