[Standard of birth weight for gestational age in 55706 healthy newborns in a public maternity of Buenos Aires]. / Estándar de peso para la edad gestacional en 55706 recién nacidos sanos de una maternidad pública de Buenos Aires.

UNLABELLED: Birth-weight-for-gestational-age patterns in Argentina are scarce and outdated. The same study has been performed within our institution for 8 years already. Our hypothesis is that there could have been population changes with repercussions on fetal growth. The objectives were: 1) to determine new normal values of birth weight (BW)-for-gestational-age; 2) to study growth speed and acceleration, and 3) to compare these new results between trienniums. POPULATION: All liveborn babies between 1988-1998 (n = 67,857) were included. Those with BW lower than 500 g, gestational age (GA) lower than 25 weeks or mistakes in the appraisal of GA and outliers (birth-weight-for gestational-age > 2.5 DS of the median) were excluded. Those without maternal or obstetric history that could have influenced the BW were defined as "healthy newborns" (n = 55,706). The software Persi, that employs 34 of the 93 variables included in the Perinatal Clinical Record (SIP/OPS/OMS, Agustina v 5.1), was used. Birth weight median, standard deviation and error, coefficient of variation, skewness and kurtosis's coefficients, real and polynomial percentiles, standard distribution (Z), and the corresponding charts were generated in an automatic way for each gestational week and through the use of the method of least squares (polynomial models up to 4th grade). Results were as follows: maximum variability 15% as from the 30th week, maximum absolute speed in the 36th week (263 g/week) and a positive acceleration, up to the 36th week, and then a negative one (maximum -127 g/week2 in the 42nd week) was observed. Skewness varied between -0.247 (31st week) and 0.129 (38th week), and kurtosis was around 3, from which it can be inferred that the population has a normal distribution. Compared to the score z, the new curves showed a maximum error of 1.53% for the 10 percentile and 1.50% for the 50 percentile. By analyzing the data by trienniums (88-91, 91-93, 94-96 and 97-98) a growing mean BW (3243 +/- 539 g to 3286 +/- 508 g; p < 0.001) and 10 percentile (2600 to 2690 g, p < 0.001) trend was appreciated. IN CONCLUSION: new values of birth weight-for-gestational-age were determined, and a secular increase trend of the mean birth weight (+43 g) was observed.