臀位在孕早期十分常见，但由于多数胎儿在临产前可自动转为头位，因此随着孕周增加，臀位发生率下降。[3]Scheer K, Nubar J. Variation of fetal presentation with gestational age. Am J Obstet Gynecol. 1976;125:269-270.http://www.ncbi.nlm.nih.gov/pubmed/1266909?tool=bestpractice.com[4]Nassar N, Roberts CL, Cameron CA, et al. Diagnostic accuracy of clinical examination for detection of non-cephalic presentation in late pregnancy: cross sectional analytic study. BMJ. 2006;333:578-580.http://www.ncbi.nlm.nih.gov/pubmed/16891327?tool=bestpractice.com在所有单胎足月分娩中，臀位患病率为 3% 至 4%。[1]Cunningham F, Gant N, Leveno K, et al. Williams obstetrics. 21 ed. New York: McGraw-Hill. 1997.[2]Kish K, Collea JV. Malpresentation and cord prolapse. In: DeCherney AH, Nathan L, eds. Current obstetric and gynecologic diagnosis and treatment. New York: McGraw-Hill Professional. 2002.足月前不同孕周臀位患病率如下：[3]Scheer K, Nubar J. Variation of fetal presentation with gestational age. Am J Obstet Gynecol. 1976;125:269-270.http://www.ncbi.nlm.nih.gov/pubmed/1266909?tool=bestpractice.com
28周以前33%
29至32周14%
33至36周9%
37至40周6%
