MONDAY, April 20, 2009 (HealthDay News) -- Newborns who were not breathing at birth and had to be resuscitated have an increased risk of having a low IQ, even if they showed no signs of mental problems in early infancy, British researchers report.
It has been thought that when the cause of the mental retardation and cerebral palsy is a period of lack of oxygen, newborns will show signs of brain damage immediately following birth called encephalopathy. The signs of encephalopathy can be seizures, abnormalities of muscle tone, abnormal movements and/or an abnormal mental state. It has also been assumed that newborns who require resuscitation at birth but are free of encephalopathy will have normal growth and development.
"It was felt that if infants were neurologically normal after resuscitation, then they were going to do OK later," said Dr. Maureen Hack, from Rainbow Babies and Children's Hospital at Case Western Reserve University in Cleveland, and author of an accompanying journal editorial.
"These researchers found that infants who were asymptomatic had lower IQs than children who needed no resuscitation," Hack said. "Since there are a lot of children who need resuscitation but have no symptoms, there are going to be a lot of children who have lower IQs at school age," she said.
However, Hack does not think the findings of the study are convincing. For example, the differences in IQs between the children who needed resuscitation at birth were not significantly different from those who did not need to be resuscitated, she said.
Despite this, the results seem to make sense, Hack said. One problem is how the effects of low oxygen were evaluated in the study, she noted.
"The neurologic exam after birth is a subjective exam," Hack said. "To say a child is normal or abnormal based on a clinical exam is difficult. To say that if they have symptoms, they may have problems, and if they don't have symptoms, they are going to be fine is a bit naive. The results make sense, but the results need to be replicated."
The report is published in the April 21 online edition of The Lancet.
For the study, a research team led by Dr. David Odd, from the Neonatal Intensive Care Unit at Southmead Hospital in Bristol collected data on children who participated in the Avon Longitudinal Study of Parents and Children.
The researchers looked at children who were resuscitated at birth but had no symptoms of encephalopathy, which is any disease of the brain that changes brain function or structure. Among these children, 815 had no further neonatal care, and 58 had care for encephalopathy. They compared these children with 10,609 children who did not need to be resuscitated at birth, had no symptoms of encephalopathy, and received no neonatal care.
To assess brain function, Odd's group measured IQ when the children were an average of 8.6 years old. A score of less than 80 was considered a low IQ.
The researchers found that children who had to be resuscitated, but did not have symptoms of encephalopathy, had a 65 percent increased risk of having a low IQ. Children who had to be resuscitated and had symptoms of encephalopathy had more than a sixfold risk of having a low IQ.
Since there are many more children who did not have symptoms of encephalopathy after being resuscitated, they have a greater effect on society, Odd's team noted.
"Infants who needed resuscitation, even if they did not develop encephalopathy in the neonatal period, had a substantially increased risk of a low full-scale IQ score...The data suggest that mild perinatal physiological compromise might be sufficient to cause subtle neuronal or synaptic damage, and thereby affect cognition in childhood and potentially in adulthood," the authors concluded.
Hack noted that improved prenatal care has reduced the number of infants who need to be resuscitated. "Modern care does prevent as much as possible," she said.
Dr. John Fiascone, medical director of the Neonatal Intensive Care Unit at Tufts University School of Medicine in Boston, doesn't find the study convincing. "The concept of a continuum of brain damage is intuitively appealing. However, this study is not proof of that concept," he said.
"The biggest weakness with the paper is that about 50 percent of infants eligible for evaluation were, in fact, not evaluated," Fiascone said. "The group differences in IQ are not convincing. For example, the reference group has an average full scale IQ of 105 while the asymptomatic group has 104. Because of the large number of babies, this difference may be statistically significant, but what is the meaning for an individual of a difference of one point in their IQ? Probably nothing at all," he said.
The authors indicated that the rate of a low IQ is 7 percent in the reference group and 10 percent in the asymptomatic group, Fiascone noted. "A 3 percent difference is unimpressive in the setting where 50 percent of eligible infants were not tested," he said.
For more about encephalopathy, visit the U.S. National Institute of Neurological Disorders and Stroke.