Small fetal size: a risk factor for breech birth at term

Objective: To examine fetal size as a risk factor for breech birth at term. Methods: Singleton breech or cephalic births of gestational age greater th an or equal to 37 weeks in New South Wales (NSW), Australia from 1990 to 19 96 were analyzed. Birthweight percentile was used as a measure of fetal siz e at the time of birth. Factors associated with breech birth at term were a nalyzed using logistic regression. Results: There were 18 914 singleton bre ech and 540 164 cephalic births in the study period. The important independ ent predictors of breech birth at term were advancing maternal age, primipa rity, female sex and small size for gestational age. Infants < 10th percent ile had an adjusted odds ratio of 1.33 (95% CI 1.28-1.38) for breech birth at term compared with 25th-75th percentile infants. Conclusions: Breech bir th at term was associated with smaller fetal size for gestational age. This was shown directly through an association with birthweight-for-gestational -age percentiles and indirectly through association with female sex, primip arous birth and congenital anomalies. (C) 1999 International Federation of Gynecology and Obstetrics.