Cerebral Palsy Rates Decline in Very Low Birthweight Children

LIVERPOOL, England, Jan. 5 -- Premature babies have a better chance of survival without severe neurological impairment than they did a generation ago, according to researchers here.

During the 1980s, the rate of cerebral palsy among infants born at less than 1,500 g, and those from multiple pregnancies had increased, but more recent reports suggest that the rate in Europe has begun to fall, Mary Jane Platt, M.D., of Liverpool University here, and colleagues, reported in the Jan. 6 issue of The Lancet.

In an editorial commenting on this study, Maureen Hack, M.D., and Deanne Costello, M.D., noted that the European data are consistent with recent findings from their own institution, Case Western Reserve in Cleveland.

To track the trend, the researchers analyzed the distribution and frequency of cerebral palsy by sex and neurological subtype for very low birthweight (VLBW) infants born in the years 1980 to 1996. The investigators used pooled data from 16 European centers, known as the Surveillance of Cerebral Palsy in Europe (SCPE).

Over 17 years 1,575 VLBW infants were born with cerebral palsy. Of these, 414 (26%) weighed less than 1,000 g, and 317 (20%) were from multiple pregnancies. Ninety-four percent of these infants (1,426) had spastic cerebral palsy, which was unilateral (hemiplegic) in 336 (24%).

The birth rate for live-born VLBW infants and those born at less than 32 weeks' gestation fell from 6% in 1980 (60.6 per 1,000) to 4% in 1996 (39.5 per 1,000), the researcher reported.

However, the decline, related to a reduction in the frequency of bilateral spastic cerebral palsy, occurred mainly in the infants weighing 1,000 to 1,499 g.

The occurrence rate of cerebral palsy among infants weighing less than 1,000 g did not change significantly, although it decreased for survivors born after 1990.

In addition, the researchers found that the frequency of cerebral palsy was higher in male than in female babies in the group weighing 1,000-1,499 g: 61.0 (CI 53.8-68.2) vs. 49.5 (CI 42.8-56.2 per 1,000 live births; P=0.0025) but not in the group below 1,000 g.

The researchers speculated that this might be due to chance, or might reflect higher survival of female infants in the higher birthweight group, but not evident among those with the lowest birthweight and highest mortality.

Among children of birthweight 1,000 to 1,499 g, there was a significant decline in the rate of cerebral palsy with inability to walk (P=0.001), which matched the overall reduction in cerebral palsy.

Nevertheless, the researchers noted that clinical profile of children with this form was constant for the duration of the study. The proportion of children unable to walk does not seem to have changed over time in either birthweight group, with 35% of children with bilateral spastic cerebral palsy unable to walk and 24% with an IQ of less than 50.

As for the risk in multiple births, the higher proportion of infants with cerebral palsy coming from multiple pregnancies simply parallels the overall rise in the proportion of VLBW infants coming from multiple pregnancies, the researchers said.

Dr. Platt said it is unclear whether the reduction in the risk of cerebral palsy occurs in infants of slightly greater maturity at delivery or is due to a change in clinical practice resulting in earlier delivery of infants already at risk.

In addition, evidence suggests that part of the reduction is a result of general improvement in neonatal care, Dr. Platt wrote.

Analyzing the pooled data produced problems, the investigators said, since centers differed in their ability to provide specific information, such as birthweight- or gestational-age-specific data.

Additionally, there was a large and probably random variation in the rate per 1,000 survivors in the lowest birthweight group, resulting from the small number of infants with cerebral palsy. This might have affected the precision of estimates in the early years of the study.

In conclusion, Dr. Platt wrote, this paper presents evidence that infants weighing less than, 1,500 g, and in particular those weighing less than 1,000 g now have a better chance of survival than previously. More important, she said, "they have a better chance of survival without severe neurological impairment, which demonstrates that improvement in neonatal care has not resulted in increased survival at the cost of substantial morbidity."

In the accompanying editorial. Drs. Hack and Costello wrote that the European experience is consistent with findings from Case Western Reserve for infants of less than 1,000 g birthweight born between 2000 and 2002.

Yet, they said, there is no cause for complacency. Cerebral palsy was associated with major disabilities in the SCPE study, including an inability to walk and severe mental retardation.

Furthermore, they said, both the SCPE study and data from the U.S. have recorded an increase in the number of live births of very low birthweight infants, which might lead to an increase in the number of children with cerebral palsy. Therefore every effort needs to be invested in the prevention of preterm birth and its associated brain injury.