Altitude effect on birth weight and prematurity in the Province of Catamarca (Argentina).

OBJECTIVES

To analyze the effect of altitude on weight and prematurity at birth in the Province of Catamarca (Argentina), between the years 1994 and 2003.

METHODS

Records of 22,628 newborns were collected from the vital statistics of the census of Catamarca. Weight was recategorized to include low birth weight (<2,500 g), and gestational age was divided into births that had occurred before or after 37 weeks (preterm or at term births). Altitude was also recategorized (<1,500 m, 1,500-2,000 m, and > 2,000 m). Nonparametric statistical tests were performed.

RESULTS

Differences were found in birth weight between sexes and in the incidence of low birth weight depending on altitude. This pattern changed according to gestational age, because those sexual differences were nonexistent or lower in preterm neonates with certain advantages for females. Moreover, it was found that the effects of hypoxia were not reflected in birth weight until later stages of intrauterine development.

CONCLUSIONS

To be female appears to be a benefit under conditions of prematurity and high altitude. The increased incidence of prematurity due to altitude increase may reflect an adaptive advantage of preterm birth under these conditions.