Background: The quantitative measurement of the normal anal position by anal position index (API) has been reported from various institutes. The existing API data appear to vary among the ethnic differences. To date, the normal anal position in Thai children has never been reported.
Objective: Aim of the present study was to establish the normal values of the API in Thai newborns.
Material and Method: A cross-sectional study of 403 normal newborn born at Srinakharinwirot University Hospital between November 2003 and September 2004 was performed. Demographic data and anal position index are reported separately for each gender split. Correlations between API and other anthropometric parameters were tested.
Results: There was significant difference of API between males (0.51 + 0.07; 95% CI 0.50 to 0.52) and females (0.38 + 0.08; 95% CI 0.37 to 0.39). API was not different between preterm and term newborn in each gender split. API had no significant correlation with gestational age (r = 0.018, p-value = 0.71), birth weight (r = 0.014, p-value = 0.79), birth length (r = 0.02, p-value = 0.69) and head circumference (r = 0.047, p-value = 0.35).
Conclusion: Anal position indexes in Thai newborn infants are 0.51 and 0.38 in male and female, respectively. API had no correlation with gestational age and other anthropometric parameters such as birth weight, length, and head circumference.

Keyword : Anal position index, Normal anal position, Newborn, Thai