To the Editor.
—The study by Cnattingius et al1 attempted to control many variables, leaving advanced maternal age as an independent risk factor for increasing perinatal morbidity and mortality. However, we have several concerns about the methods used.Most significantly, in an article attempting to show an association between advanced maternal age and increased perinatal morbidity and mortality, we find it interesting that no specific mention is made of the neonatal outcome, such as chromosomal aneuploidy. What percentage of these infants had structural anomalies? Indeed, there is no mention of the specific causes of adverse neonatal outcomes. It is imperative in a study of this nature to control for fetal as well as maternal variables.Additionally, we would like more information on the nature of prenatal care in Sweden. What is routine to the investigators may not be routine in the United States. Specifically, what percentage of the population