Among 6 221 001 live births in California from 1991 to 2001, 8397 children with cerebral palsy provided an overall prevalence of 1.4 per 1000 live births. Over the 10-year study period, the prevalence of cerebral palsy did not vary significantly by birth year (data not shown). Almost 63% of cerebral palsy cases were of the spastic or dyskinetic subtypes (). Quadriparesis was the most common distribution of limb involvement, followed by paraparesis and hemiparesis. Three-quarters of cases were categorized as moderately severe or severe.
Clinical Characteristics of 8397 Infants With Cerebral Palsy Among 6.2 Million Births in California, 1991–2001
In crude assessments of ethnic disparities in cerebral palsy, black children were 29% more likely to have cerebral palsy than white children (). Asian children were 20% less likely to have cerebral palsy than white children, and there was no difference between Hispanic and white children. Women who were younger (aged <18 years), older (aged ≥35 years), had no prenatal care, or had low insurance status had an increased risk of having a child with cerebral palsy. Compared with women with a college diploma, women with lower educational attainment were more likely to have a child with cerebral palsy. The effect of maternal education on the risk of cerebral palsy demonstrated an inverse dose-response relationship; compared with college graduates, mothers with primary school or no education (RR: 1.33) demonstrated the highest risk, whereas mothers with a high school diploma (RR: 1.21) or some college (RR: 1.14) exhibited a more modest increased risk of cerebral palsy ().
Univariate Risks for Cerebral Palsy Among 6.2 Million Live Births in California, 1991–2001
Thirty-seven percent of children with cerebral palsy were born at moderately low (16%) or very low birth weight (21%). Very low birth weight infants were 24 times more likely to have cerebral palsy than normal birth weight infants, and very premature infants (<28 weeks' gestation) were 26 times more likely to have cerebral palsy than infants born term ().
Black children were more likely than white children to have been born at very low (3.5% vs 1.3%, P = .0001) or moderately low (9.5% vs 4.6%, P = .0001) birth weight. Similarly, black children were more likely to have been born premature (<37 weeks ' gestation) than white infants (20.4% vs 11.9%, P = .0001). Asian children were less likely to be born at very low birth weights than white children (1.2% vs 1.3%, P = .02) but more likely to have been born with moderately low birth weight (6.5% vs 5.1%, P = .0001) when compared with white children.
To assess whether ethnic differences in birth weight or gestational age explain ethnic disparities in the risk of cerebral palsy, we performed stratified analyses (). Among normal birth weight infants, there was no difference in the risk of cerebral palsy between blacks and whites (RR: 1.00 [95% CI: 0.89–1.12]). In contrast, black infants who were born of moderately low (RR: 0.71 [95% CI: 0.59–0.85]) or very low (RR: 0.79 [95% CI: 0.68–0.91]) birth weight were less likely to be diagnosed with cerebral palsy than comparable white infants. Similar results were obtained when we stratified by gestational age. That is, although there was no difference in the risk of cerebral palsy between black and white infants born term (RR: 1.04 [95% CI: 0.9–1.16]), very premature (<31 weeks' gestation) black infants were less likely to have cerebral palsy than comparable white infants (RR: 0.81 [95% CI: 0.69–0.95]).
Race As a Risk Factor for Cerebral Palsy, Stratified by Infant Birth Weight and Gestational Age
In a logistic regression model, black race was no longer a risk factor for cerebral palsy after controlling for birth weight and, in fact, was associated with decreased risk (OR: 0.87 [95% CI: 0.80–0.94]). Similarly, controlling for gestational age eliminated the apparent adverse effect of black race on cerebral palsy (OR: 0.95 [95% CI: 0.87–1.03]). Thus, both stratified and logistic regression analyses suggest that the increased rate of low birth weight and prematurity alone accounts for the increased risk of cerebral palsy observed in black infants.
In contrast, controlling for maternal education and insurance status in a logistic regression model did not eliminate the increased risk of cerebral palsy observed in blacks (OR: 1.3 [95% CI: 1.2–1.4]), suggesting that low socioeconomic status does not fully explain the racial disparity between blacks and whites. Yet socioeconomic markers were associated with cerebral palsy in crude analyses (). Furthermore, maternal race was highly correlated with maternal educational attainment; for instance, 84% of mothers with the lowest educational level (0–5 years) were Hispanic. Maternal race also was correlated with insurance status. Hispanics had the highest rate of government or no insurance (62%) and Asians had the lowest rate (6%). Therefore, to determine the independent contributions of sociodemographic risk factors for cerebral palsy within each racial and ethnic subgroup, we performed stratified multivariate analyses.
Among whites, decreasing maternal educational attainment was independently associated with increasing risk of cerebral palsy in a dose-response fashion (). In multivariate analysis, Hispanic women with 0 to 5 years of education also were more likely to have a child with cerebral palsy than their counterparts who were college graduates (OR: 1.3 [95% CI: 1.04–1.5]). In contrast, maternal education was not associated with cerebral palsy risk among blacks.
Independent Effects of Sociodemographic Factors on Risk of Cerebral Palsy in a Multivariate Model, Stratified by Racial and Ethnic Groupsa
Black Hispanic, and white women who delivered without receiving prenatal care had a significant twofold increased risk of cerebral palsy, compared with their counterparts who received early prenatal care (). For these 3 racial and ethnic groups, lack of prenatal care was associated with an increased risk of cerebral palsy even after adjusting for birth weight gestational age (data not shown). Asian women who did not receive prenatal care also demonstrated a twofold increased risk of cerebral palsy, although this was not a statistically significant finding.
Older Asian, Hispanic, and white mothers were 32% to 45% more likely to have a child with cerebral palsy than women who were aged 18 to 34 years (). Adolescent childbearing was significantly associated with cerebral palsy only among Hispanic women (OR: 1.2 [95% CI: 1.02–1.3]), although a similar trend was seen in blacks (OR: 1.3 [95% CI: 0.97–1.8]).
When we restricted the analyses in and to children with moderate or severe cerebral palsy, the findings remained essentially unchanged, except the effect sizes became slightly larger (data not shown). In additional sensitivity analyses, we limited the stratified analyses to children with spastic or dyskinetic cerebral palsy, because this group is likely to be etiologically distinct from infants with hypotonic and ataxic cerebral palsy. The significant findings in and remained unchanged when the analyses were restricted to spastic or dyskinetic cerebral palsy. However, the risk of spastic or dyskinetic cerebral palsy was elevated in blacks compared with whites both among normal birth weight (RR: 1.3, P = .0004) and among infants of term gestational age (RR: 1.3, P = .0004). Hispanics were similarly at increased risk of spastic or dyskinetic cerebral palsy when compared with whites, in both normal birth weight (RR: 1.1, P = .02) and term gestational age (RR: 1.5, P = .001) strata. In contrast, black infants were less likely than white infants to have ataxic cerebral palsy (RR: 0.6 [95% CI: 0.3–0.97]) or hypotonic cerebral palsy (RR: 0.4 [95% CI: 0.2–0.5]).