Preterm birth linked to increased risk for cerebral palsy

**Moster D. JAMA. 2010;304:976-982.**

Delivery before or after 40 weeks’ gestational age may increase a child’s chances of developing cerebral palsy, study results indicate.

“One of the strongest predictors of [cerebral palsy] is preterm birth, with the risk of [cerebral palsy] increasing steadily with earlier delivery,” researchers from Norway wrote. “Although risk is lower among term births, about three-fourths of all infants with [cerebral palsy] are born after 36 weeks.”

To investigate the potential association between gestational age within the term range and risk for cerebral palsy, the researchers conducted a population-based follow-up study using the Medical Birth Registry of Norway.

Infants born at 37 to 44 weeks’ gestational age between 1967 and 2001 were included in the analysis, according to the researchers, and follow-up was conducted up to 2005. Other data included birth year, mother’s education level, father’s education level, maternal age and immigrant status of parents.

The researchers discounted infants with missing data on gestational age and preterm or postterm birth status. Additionally, infants with birth weights that were inconsistent with their gestational ages, those who were multiple births, those with malformations and those who died before 4 years of age were not included.

Of the infants born during the study period, 1,682,441 warranted inclusion — 1,938 of whom had cerebral palsy. These data equated to a prevalence of 1.15 per 1,000 births (95% CI, 1.1-1.2).

Analysis revealed that infants born at 40 weeks’ gestational age were least likely to have cerebral palsy, with a prevalence of 0.99 cases occurring per 1,000 live births (95% CI, 0.9-1.08).

Prevalence rose, however, to 1.91 cases per 1,000 (95% CI, 1.58-2.25) for infants born at 37 weeks’ gestational age. The researchers also reported a risk of 1.9 (95% CI, 1.6-2.4) for this population.

Prevalence decreased slightly at 38 weeks, to 1.25 per 1,000 (95% CI, 1.07-1.42), as did the RR, declining to 1.3 (95% CI, 1.1-1.6).

Data, however, demonstrated an increased risk for cerebral palsy as gestational age at time of delivery increased, according to the researchers. Prevalence at 42 weeks was 1.36 per 1,000 (95% CI, 1.07-1.42), and the risk was 1.4 (95% CI, 1.2-1.6).

Prevalence was even higher for infants born after 42 weeks’ gestational age, with results projecting a rate of 1.44 per 1,000. The risk, however, was similar to that observed at 42 weeks.

For these results, gestational age was measured using time from last menstrual period. The researchers noted, however, that this method is often prone to error. Therefore, they used ultrasound measurements to determine gestational age for the portion of the study population who had the data available.

According to analysis with using the ultrasound measurements, the researchers said the association between gestational age and risk for cerebral palsy was stronger. The prevalence among infants born at 40 weeks was 0.36 per 1,000 (95% CI, 0.18-0.54). Infants born at 37 weeks, however, had a prevalence of 1.17 per 1,000 and a RR of 3.7 (95% CI, 1.5-9.1) when compared with those born at 40 weeks.

Also, when using this method, infants born at 42 weeks had a prevalence of 0.85 per 1,000 (95% CI, 0.33-1.38) and a risk of 2.4 (95% CI, 1.1-5.3).

The researchers also noted that prevalence of cerebral palsy at 37 weeks’ gestational age or more decreased from 1.4 per 1,000 (95% CI, 1.3-1.5) during 1967 to 1971 to 0.7 per 1,000 (95% CI, 0.6-0.8) during 1997 to 2001. The link between gestational age and cerebral palsy, however, remained the same during the study period.

Although the study provides new information on the development of cerebral palsy in infants, the researchers said they cannot determine any causes for the disorder. They also noted that they are unsure whether delivery time affects cerebral palsy or if an aspect of cerebral palsy interrupts delivery time.

“Until the biological mechanisms for these patterns of risk in term and postterm births are better understood, it would be hasty to assume that interventions on gestational age at delivery could reduce the occurrence of [cerebral palsy],” the researchers wrote.