[Definition of intrauterine growth retardation].

In order to answer the question as to the limit of intrauterine foetal growth retardation, we compared three weight values at birth: two standard deviations below the mean, namely the fifth and tenth percentiles. The comparisons were made on the intrapartum and early neonatal mortality rates of 19,256 infants born during 1980 in "La Paz" Maternity Hospital of Madrid. Our results show that we have to consider as newborn with a growth retardation those infants whose weight at birth is lower than the fifth percentile for their gestational age and sex. In this group of infants, the intrapartum and early neonatal mortality rates are significantly higher than among newborn with a superior weight. At the same time, we found that the mortality among newborn with a weight between the fifth and tenth percentile was not significantly higher than that observed among infants with a weight at birth greater than the tenth percentile.