Birth weight charts for gestational age in 63 620 healthy infants born in Peruvian public hospitals at low and at high altitude

Aim: To construct distribution curves for birth weight, length and head circumference using a large sample of infants born at low (150 m) and high (3000-4400 m) altitude. Methods: Cross-sectional analysis of a perinatal database. All live singleton deliveries from public hospitals during 2001-2006 (gestational age from 26 to 42 weeks) with no history of perinatal deaths or smoking and no current obstetric complications (n = 63 620) were included. Fractional polynomial regression models were used to smooth curves for each gestational age. Results: Mean and median birth weight differences between those born at low and high altitudes reached statistical significance after 35 and 33 weeks, respectively. Values of the 10th percentile were higher at low altitude from 36 weeks, whereas values at the 90th percentile were different from 34 weeks. In the Peruvian growth curves, birth weight was greater at each gestational age than in the curves derived by Lubchenco. Conclusion: Altitude affects growth patterns; these growth standards will provide useful references for the care of the newborn in highland populations. In addition, the data have implications for the antepartum management of pregnant patients undergoing sonographic evaluation of fetal weight in whom new definitions of what represents small or large for gestational age in utero can result in differences in time or mode of delivery.