NEW YORK (Reuters Health) - Black infants have a somewhat higher risk of Cerebral Palsy, according to a new study, and the increase appears to be tied to their greater likelihood of being born underweight.

In fact, after taking birth weight into account, blacks are much less likely than whites to be diagnosed with the crippling neurologic disorder, although why that's the case is a mystery, the scientists said.

"Low birth weight infants have a much higher risk of Cerebral Palsy," said Dr. Yvonne Wu, a pediatric neurologist at the University of California, San Francisco who led the study. She told Reuters Health, "If we could eliminate the racial disparity in low birth weight deliveries, then we would also eliminate the differences in Cerebral Palsy between blacks and whites."

"We need these big population studies to get at those kind of details," said Dr. Nancy Murphy, a pediatrician at the University of Utah in Salt Lake City, and chair of the American Academy of Pediatrics Council on Children With Disabilities.

The new research suggests that efforts to improve prenatal care among black mothers, particularly teens, might reduce the incidence of Cerebral Palsy among blacks, according to the researchers. Women who receive early and high-quality prenatal care tend to have healthier babies than those who don't get the checkups.

"We found that women who received prenatal care had a lower risk of having a child with Cerebral Palsy," Wu said. "However, we don't know whether the prenatal care itself protects women from having a child with Cerebral Palsy, or whether women who receive prenatal care differ in some other way that reduces the risk of having a child with Cerebral Palsy."

For the study, published online today in the journal Pediatrics, Wu and her colleagues analyzed medical records of 6.2 million births in California between 1991 and 2001. Among them, about 8,400 infants had been diagnosed with Cerebral Palsy, for a rate of 1.4 cases per 1,000 live births.

That's somewhat less than previous estimates, which have put the prevalence of Cerebral Palsy at between 2 and 2.5 cases per 1,000 live births.

The lower rate reflects the fact that the California researchers did not include children with mild cases of Cerebral Palsy who did not qualify for state services, Wu explained.

Of the nearly 8,400 babies with Cerebral Palsy, 758 were black, 2,878 were white, 3,963 were Hispanic and 656 were Asian.

Blacks were about 30 percent more likely than whites to have Cerebral Palsy, the researchers found. Hispanics had roughly the same odds as whites, while Asians appeared to be least likely to be diagnosed with the condition.

Babies born underweight or premature were up to 24 times more likely to be diagnosed with Cerebral Palsy, the researchers said, and both risk factors were much more common among blacks. But after accounting for low birth weight, blacks were between 21 percent and 29 percent less likely than whites to be diagnosed with Cerebral Palsy, according to the researchers.

Women who did not have prenatal care had more than twice the typical chance of giving birth to a baby with Cerebral Palsy, the researchers found. Those who did not graduate from high school also had a higher risk.

Although Wu said her findings point to a possible role for prenatal care in preventing Cerebral Palsy among blacks, an example from recent history might temper optimism for the strategy. In the 1970s, doctors began advocating that women use electronic fetal monitors as a way to prevent Cerebral Palsy.

"The thinking was that if you could detect fetal distress by monitoring the baby's heart rate prior to delivery, you could perform a cesarean section earlier, and thereby prevent brain injury. However, even though electronic fetal monitoring leads to about 40 percent more cesarean sections, it has not been effective in preventing Cerebral Palsy," she said.

Teasing out the impact of prenatal care on infant health, added Murphy, who was not involved in the study, is "exquisitely complicated."

A study involving almost 1.7 million children in Norway suggests that being born early or late slightly increases the risk of Cerebral Palsy. Cerebral Palsy includes several disorders that affect the brain and nervous system and believed to result due to an injury in utero or as an infant. Kids born from 1967 to 2001 at 37 to 44 weeks were studied. Kids born at 40 weeks had a 1 in 1000 chance of having Cerebral Palsy, while those born at 37 and 38 weeks had a 2 in 1000 and 1.25 in 1000 chance, respectively. Forty two weeks increased it to 13.6 in 1000 and after 44 weeks the odds were 1.44 in 1000. Researchers think either the brain of newborn’s brain is vulnerable outside the normal gestational period or the biology of Cerebral Palsy increases the likelihood of an early or late birth.

An examination of data conducted by Dag Moster, M.D., Ph.D., of the University of Bergen, Norway found that infants entering the world at term or later are associated with an increased risk of Cerebral Palsy (CP). This JAMA (Journal of the American Medical Association) published study first appeared on September 1, 2010.

CP is the most common cause of physical disability children. Non-progressive disorders of movement and posture are the key symptoms of this prevalent ailment.

Using the Medical Birth Registry of Norway's 1,682,442 births between 1967 and 2001, Moster and colleagues examined the relation of CP risk with gestational age among term and post term births that possessed no congenital anomalies. The group was followed up through 2005 by linkage to other national registries that track Norwegian lifecycles.

1,938 were identified as having Cerebral Palsy.

The study's authors state: " One of the strongest predictors of CP is preterm birth, with the risk of CP increasing steadily with earlier delivery. Although risk is lower among term births, about three-fourths of all infants with CP are born after 36 weeks. Within this range of term births, there are few data on the possible association of CP with gestational age".

Risk for CP was higher with earlier or later delivery, but those born at the 40 week mark showed almost zero occurrence of CP. Those born at 37 weeks had a 90% increased risk of displaying symptoms of Cerebral Palsy. At 38 weeks, a 30% higher risk. Forty-two weeks and after deliveries had a 40% increased risk.

Clinicians typically regard term births (37-41 weeks) as low risk, with the possibility of increased risk with post term delivery. This standard definition of term does not correspond well with the period of lowest risk for CP in this study or with the weeks when most infants are born.

Weeks 37 and 38 seem more to resemble weeks 42 and 43, both in CP risk and in the general likelihood of delivery, leaving 39 to 41 weeks as the optimum time for delivery. If the time of delivery affects CP risk, then intervention at 40 weeks might reduce CP risk, while elective delivery at 37 or 38 weeks might increase it.

If infants prone to CP are disrupted in their delivery times, the prevalence of CP would be unchanged regardless of time of delivery.

The research authors finally concluded: "Until the biological mechanisms for these patterns of risk in term and post term births are better understood, it would be hasty to assume that interventions on gestational age at delivery could reduce the occurrence of CP".

What is Cerebral Palsy?

Cerebral Palsyis a term which encompasses a set of neurological conditions that cause physical disability in human development - they affect the brain and nervous system. The word cerebral refers to the area in the brain that is affected, while palsy means complete or partial muscle paralysis, frequently accompanied by loss of sensation and uncontrollable body movements or tremors. Cerebral means related to the brain or cerebrum.

A person with Cerebral Palsy will generally show symptoms during the first three years of life. A child/baby with Cerebral Palsy may have some of the signs and symptoms below:

• Achieves developmental milestones, such as crawling, walking, or speaking, later than his/her peers.
• Can be easily startled.
• Crawls in an unusual way.
• Favors one side of the body over the other.
• Has abnormal muscle tone - the child will slouch while sitting. Muscle tone refers to a person's automatic ability to tighten and relax muscle when required.
• Has bad coordination and balance (ataxia).
• Has bladder control problems.
• Has bowel movement control problems.
• Has difficulty feeding and sucking.
• Has hearing problems.
• Has involuntary, slow writing movements (athetosis).
• Has overdeveloped or underdeveloped muscles (has floppy or stiff movements).
• Has problems swallowing.
• Has problems with eyesight.
• Has seizures.
• Lies down in awkward positions.
• Muscles are stiff and contract abnormally (spastic paralysis).
• Range of movements are limited.