"Prolonged infant crying is not only stressful for children's families, it also can be a warning sign for a delay in children's mental development," says Dr Duane Alexander, director of the NICHD. "This study strongly suggests that we need to monitor children who cried for prolonged periods as infants to ensure that they're developing appropriately for their age level."
Researchers have studied colic, which is persistent crying that occurs during the first few weeks of life up to three months of age. However, there has been little research on prolonged crying, which continues after an infant reaches three months of age, explains the study's first author, Malla Rao, PhD, who conducted the study while he was a researcher in NICHD's Division of Epidemiology, Statistics, and Prevention Research.
To conduct the current study, Dr Rao and his coworkers analyzed information from an earlier study of pregnant women in Norway and Sweden with one or two previous singleton births. After delivery, the infants were evaluated during routine preventive care visits at six and 13 weeks and again at six, nine and 13 months of age.
The researchers compared maternal and infant characteristics of normal infants, infants with colic, and those with prolonged crying. The three groups did not differ in the occurrence of birth complications or other occurrences of the birth process, such as injury during birth or admission to neonatal intensive care units. Of the 327 children whose records were analyzed for the study, 48 were found to have had colic and 15 were found to have had prolonged crying.
The researchers found that at five years of age, the 15 children who had prolonged crying as infants had, on average, IQ scores 9 points lower than those who had no crying problems. The prolonged crying group also had significantly poorer eye-hand coordination. There was no significant difference in IQ scores and eye-hand coordination scores between children in the colic group and the normal infant group.
In addition, the researchers obtained information on personality traits on a subset of nine children within the prolonged crying group study who had taken a personality inventory test. Although the researchers did not obtain enough information on a large enough number of children to allow them to draw any firm conclusions, the children's scores suggested that children who cry for prolonged periods during infancy may also be more likely to later exhibit behavioral problems such as hyperactivity or problems with discipline.
To explore the possibility that factors other than prolonged crying might have been responsible for the children's developmental delays, Dr Rao and his colleagues compared the home environments and overall health of children in the three groups. They found no differences. The study also examined the effects of genetic factors, mothers' IQ, and factors like the duration of exclusive breast feeding.
"This study supports earlier findings that colic does not affect cognitive development," said Dr Rao. "Prolonged crying, on the other hand, appears to be related to cognitive problems. It is not clear whether prolonged crying is a sign of delayed developmental maturation since infants cry less as they mature, or whether irritability caused by subtle underlying neurological problems is resulting in such behavior."
The study also confirmed findings from earlier studies that
mothers who were smokers were twice as likely to have children
with colic. However, smoking was not associated with prolonged crying.