CLINICAL SECTION Clinical Opinion The incidence of cerebral palsy Mortimer G. Rosen, MD, and Janet C. Dickinson, BSN , MSW New York, Ne w York The clinician is often held responsible for obstetric events that are suspected of being related to cerebral palsy. To review the incidence of cerebral palsy and to aid the clinician in this situation, a search of published studies was conducted . Composite rates of cerebral palsy in different birth weight infants and cerebral palsy with and without serious mental retardation were calculated . The cumulative incidence rate at the age of 5 to 7 years was 2.7 cases of cerebral palsy for 1000 birth cohorts. Approximately 36% of all cerebral palsy occurred in the infant < 2500 gm. Serious mental retardation (intelligence quotient < 50) accompanied cerebral palsy approximately 30% of the time for the term infant and 18% of the time when the infant was < 2500 gm. On the basis of a past estimation that 70% of cerebral palsy is of antepartum or unknown origin, the term infant at risk for intrapartum-attributed cerebral palsy may be about 1 in 2000 term births. (AM J OBST8 GVNECOL 1992;167:417-23.)
Key words: Cer ebral palsy, incidence , mental re ta rdation Cerebra l pa lsy continues to pose a diagnostic and therapeutic d ilemma for the obstetrician beca use its various causes are poorl y u nd erstood . Electronic fetal monito ring, init iated in the ea rl y 1960s , raised hopes tha t some cases of cerebral pa lsy cou ld be p reve nted through a better mean s of eva luation of the fetus du ring labor. T od ay, studies continue to find a lack of associat ion between intrap art um fetal monitor ing and lon g-term neurologic outcome. ' Co n fou nding the incide nce issue is the fact that obs tetric p ractices and ne onatal intensive care have changed . With increased infant survival, increased ne urologic morbid ity may occu r mor e frequen tly, offsetting the overall effects of clinical practice changes! This review attem pted to evaluate current morbidit y data with res pect to the rates of cerebral palsy. Past stu d ies have genera lly found a prevalence rate of abo ut 2 per 1000 livin g infants at 7 to 10 years o f age, with ser ious mental retardation (in tellige nce quotient [IQ] < 50 ) present in 20 % to 30 % of these children.' The lar gest United States study, th e Co llaborative Perinatal Project, foun d a cerebra l pa lsy cumulative incidence ra te (which includes children with cerebral palsy who died) of 4.6 per 1000 of infants at 7 years of age! The question raise d in this review was whether th e cumuFrom the Department of Obstetrics and Gynecology, Sloane H ospital f or Women of Columbia Presbyterian M edical Center and the College of Physicians and Surgeons of Columbia University. R eprints not available.
611137971
lative incid ence of cerebral palsy has changed d uring the past 10 years, specifica lly the cu mulative incid ence in the term infant.
Methods A Med line search was conducted of all original En glish langua ge studies pu blished since 1980, with major in fa nt neu rologic damage as an end point. Unfortunatel y, although these stu dies were p ublished since 19 80, the birth dates of th e pop ulation s often went back to the 1950s. Few re cent stu d ies of the combination of mental re tard ation and cerebral pa lsy were found ; therefore studies conducted before 1980 were included when that aspect is discussed . Where poss ible, in some of the tables the birth d ates were indicated ra ther than the publicatio n d ates of the stud ies, so that the reader could consi der the possible differences in ne on atal care in the d ifferent tim e pe riods. To be includ ed in ana lyses, studies had to provide adequate raw n umbers to determine the denominator for th e rates of cerebral pa lsy either in the total population or by birth weight. Cu mu lative inciden ce at the age of 4 to 7 years was used beca use it pro vide s more information th an either a straight incidence or prevale nce rate. The cu mulative incidence rate use d all bir ths during a set period of time as the denomina tor , and n ume rator included infants with cerebral palsy who had die d . Including infants who had died has been recommended to provide as com plete a picture of cere bral palsy as possible." Prevalence ra te was not used,
417
418
Rosen and Dickinson
August 1992 Am J Obstet Gyne col
Table I. Cu mulative inciden ce of cerebral palsy per 1000 live births Study
y ear pu blished
Birth years
Country
Length of foll ow-up (yr)
R ate, excluding acquired (per 1000)
J arvis et al.? Nelson and Ellenberg" Emond et al. 10 Hagberg et al."t Holst et al.[. Dowding and Barry[3t Stanley and Watson" Riikonen et al." T or fs et al." Pharoah et al. [7 Meberg" Composite rate
1985 1986 1989 1989 1989 1988 1988 1989 1990 1990 1990
1972-197 5 1959-1966 1970 1979-1982 1978 1979-1981 1979-1981 1978-1982 1959-19 66 1984 1980-1984
Eng land Unite d States* En gland Sweden Denmark Irel and West Australia Finland California Eng land Norw ay
5 7 7 4 4 4 5 5 5 5 4
1.8 4.6 2.5 2.2 4.9 1.9 2.3 2.5 2.0§ 1.9 2.1 2.7
*Collaborative Perinatal Projec t. t Exciuded deaths before age 2. t Exciuded all congenital anom alies. §Did not indicate whether deaths were included.
because it can var y tremendousl y depending on the age of diagnosis and the len gth of time of survival. In the ColIaborative Perinatal Proj ect 15% of the children diagnosed with cerebral pals y at 12 months had died by the age of 7 years."" Studies with folIow-up at different ages, between 4 and 7 years, were qualified by stating the different ages. Cases of cerebral palsy th at were obviously cau sed post natalIy were excluded. Studies usualI y did not differentiate cerebral palsy by degree of handicap, so a stu dy's diagnosis of cerebral palsy was accepted. Figures fro m the Collaborative Perinatal Project were included to provide comparisons and becaus e that study constituted a large and essentially singular United States cerebral palsy incidence study. The figures from th e Collaborative Perinatal Project included both infants who had a diagnosis of cerebral palsy who had died and cases of cerebral palsy th at the y defined as mild (not requiring bracing, wheelchair, etc .)" because we decided th at their "mild" category would be included in alI cases of cerebra l palsy in other studies. We primarily used later published reports abou t the ColIaborative Perinat al Project because thes e categories were included. Earlier reports that excluded de aths and "mild" cerebral palsy yielded a 2.5 per 1000 rate." For types of cerebral palsy, the denominator is alI cases of cerebral palsy. When discussing the different types of cerebral palsy, th e most frequently used categories of cerebral palsy included diplegia (or paraplegia), a form of cerebral palsy where the legs are pri maril y affected ; hemiplegia, where onl y one side of the body is affected ; and quadriplegia (or tetraplegia), where three or all four limbs are affected . Extrapyramidal (or dyskinetic) cerebral palsy, including choreoathetotic and dysto nic and ataxia, was included as much as possib le whe n stu dies had th is as a distinct category.
The anal yses of cerebral palsy by birth weight were done with live births at that birth weight as denominators . Because studies used either cerebral pals y or mental retardation as starting points, both types of stud ies were considered. Howe ver , when considering studies using mental retardation as the starting point, th e primary focus was that proportion of the mentally retarded who also had cerebral palsy. Mental retardation not associated with cerebral palsy was not reviewed. Results
Excluding cases that had an obvious postnatal origin, 10 studies published since 1980 determined the cumu lative incidence rates for cerebral palsy,,"'-17 (Table I). The average cumulative incidence rate of these studies was 2.7 per 1000 livebirths. Table II describes studies that included the breakdown by type of cerebral palsy.B,9,I[.l3,17-19Years of birth, not publication, are given. Not alI the previously discussed studies were included, because not all had breakdown by type of cerebral palsy. The avera ge proportion s of the different types of cerebral palsy of all with cerebral palsy were 34% diplegia, 30 % hemiplegia, 20 % qu adriplegia, and 16% extrap yramidal. Table III includes studies that grouped cerebral palsy by birth weight." 4, s, H-17, 20 Years of birth, rather than dates of publication, are indicated for the reasons previously stated. The average pr op ortions of cerebral palsy by birth weight of all children with cerebral palsy were 36% for those weighing 2499 gm . Some of these studies an alyzed cerebral palsy rates by smaller increments of birth weight" [I , [ 3 , 14 , [6 , [ 7 (Table IV) . The increments varied too much to do an exact comparison, but the figures are helpful to determine any trends in the incidence by birth weight.
Incidence of cerebral palsy 419
Volume 167 Number 2
Table II. Distribution of cerebral palsy by type* Study
Nelson and Ellenberg"] Pharoah et aLI7 Dowding and Barry" Dale and Stanley'? Riikonen et al. 15 Hagberg et al. 11 Jarvis et al." Composite rates
Country
1959-1966 1984 1979-1981 1971-1975 1978-1982 1979-1982 1972-1975
United States England Ireland Australia Finland Sweden England
Hemiplegia (%)
Quadriplegia (%)
Extrapyramidal (%)
29 40 25 22 29 36 29 30
24 27 10 32 3:j: 7:j: 39 20
14 11 27 5 24 15 9 16
32 24 38 39 44 41 l8§ 34
*Denominators are all cases of cerebral palsy. Rows may not total 100% because some types of cerebral palsy were excluded. tBased on survivors. :j:Used term tetraplegia. §Used term paraplegia.
Table III. Distribution of cerebral palsy by birth weight* Country
2499 gm (%)
Overalliow-birth-weight births (%)
United Statest England West Australia Denmark England Norway Sweden Ireland Finland Japan California
33 47 32 40 26 27 38 32 52 52 17 36
67 53 68 60 74 73 62 68 49 48 83 64
9.2 6.7
Study
Nelson and Ellenberg" Pharoah et aLI7 Stanley and Watsonl 4 Holst et aLI2 Jarvis et al. 9 Meberg'"
Hagberg et al. II Dowding and Barry" Riikonen et al. 15 Saito et aL20 Torfs et al." Composite rates
1959-1966 1984 1979-1981 1978 1972-1975 1980-1984 1979-1982 1979-1981 1978-1982 1963-1976 1959-1966
4.1:j:
3.5
7.0 4.2 4.0 5.1 4.0 4.5 6.8 5.3
*Denominator is cases of cerebral palsy. tCollaborative Perinatal Project. :j:Figure from Dale et al, 19 Some studies analyzed trends of cumulative incidences of cerebral palsy over periods of time"!': 13-17. 19 (Fig. 1). Some studies found recent minor decreases, others found almost no change in rate, and other studies found recent minor increases. When there was a minor increase, the type of cerebral palsy that increased the most was diplegia or cerebral palsy among lowbirth-weight (LBW) infants. A few studies analyzed the occurrence of serious mental retardation among children with cerebral palsy. Table V provides the figures from those studies. 18.21. 22 The average rate of serious mental retardation (IQ
Key words: Cer ebral palsy, incidence , mental re ta rdation Cerebra l pa lsy continues to pose a diagnostic and therapeutic d ilemma for the obstetrician beca use its various causes are poorl y u nd erstood . Electronic fetal monito ring, init iated in the ea rl y 1960s , raised hopes tha t some cases of cerebral pa lsy cou ld be p reve nted through a better mean s of eva luation of the fetus du ring labor. T od ay, studies continue to find a lack of associat ion between intrap art um fetal monitor ing and lon g-term neurologic outcome. ' Co n fou nding the incide nce issue is the fact that obs tetric p ractices and ne onatal intensive care have changed . With increased infant survival, increased ne urologic morbid ity may occu r mor e frequen tly, offsetting the overall effects of clinical practice changes! This review attem pted to evaluate current morbidit y data with res pect to the rates of cerebral palsy. Past stu d ies have genera lly found a prevalence rate of abo ut 2 per 1000 livin g infants at 7 to 10 years o f age, with ser ious mental retardation (in tellige nce quotient [IQ] < 50 ) present in 20 % to 30 % of these children.' The lar gest United States study, th e Co llaborative Perinatal Project, foun d a cerebra l pa lsy cumulative incidence ra te (which includes children with cerebral palsy who died) of 4.6 per 1000 of infants at 7 years of age! The question raise d in this review was whether th e cumuFrom the Department of Obstetrics and Gynecology, Sloane H ospital f or Women of Columbia Presbyterian M edical Center and the College of Physicians and Surgeons of Columbia University. R eprints not available.
611137971
lative incid ence of cerebral palsy has changed d uring the past 10 years, specifica lly the cu mulative incid ence in the term infant.
Methods A Med line search was conducted of all original En glish langua ge studies pu blished since 1980, with major in fa nt neu rologic damage as an end point. Unfortunatel y, although these stu dies were p ublished since 19 80, the birth dates of th e pop ulation s often went back to the 1950s. Few re cent stu d ies of the combination of mental re tard ation and cerebral pa lsy were found ; therefore studies conducted before 1980 were included when that aspect is discussed . Where poss ible, in some of the tables the birth d ates were indicated ra ther than the publicatio n d ates of the stud ies, so that the reader could consi der the possible differences in ne on atal care in the d ifferent tim e pe riods. To be includ ed in ana lyses, studies had to provide adequate raw n umbers to determine the denominator for th e rates of cerebral pa lsy either in the total population or by birth weight. Cu mu lative inciden ce at the age of 4 to 7 years was used beca use it pro vide s more information th an either a straight incidence or prevale nce rate. The cu mulative incidence rate use d all bir ths during a set period of time as the denomina tor , and n ume rator included infants with cerebral palsy who had die d . Including infants who had died has been recommended to provide as com plete a picture of cere bral palsy as possible." Prevalence ra te was not used,
417
418
Rosen and Dickinson
August 1992 Am J Obstet Gyne col
Table I. Cu mulative inciden ce of cerebral palsy per 1000 live births Study
y ear pu blished
Birth years
Country
Length of foll ow-up (yr)
R ate, excluding acquired (per 1000)
J arvis et al.? Nelson and Ellenberg" Emond et al. 10 Hagberg et al."t Holst et al.[. Dowding and Barry[3t Stanley and Watson" Riikonen et al." T or fs et al." Pharoah et al. [7 Meberg" Composite rate
1985 1986 1989 1989 1989 1988 1988 1989 1990 1990 1990
1972-197 5 1959-1966 1970 1979-1982 1978 1979-1981 1979-1981 1978-1982 1959-19 66 1984 1980-1984
Eng land Unite d States* En gland Sweden Denmark Irel and West Australia Finland California Eng land Norw ay
5 7 7 4 4 4 5 5 5 5 4
1.8 4.6 2.5 2.2 4.9 1.9 2.3 2.5 2.0§ 1.9 2.1 2.7
*Collaborative Perinatal Projec t. t Exciuded deaths before age 2. t Exciuded all congenital anom alies. §Did not indicate whether deaths were included.
because it can var y tremendousl y depending on the age of diagnosis and the len gth of time of survival. In the ColIaborative Perinatal Proj ect 15% of the children diagnosed with cerebral pals y at 12 months had died by the age of 7 years."" Studies with folIow-up at different ages, between 4 and 7 years, were qualified by stating the different ages. Cases of cerebral palsy th at were obviously cau sed post natalIy were excluded. Studies usualI y did not differentiate cerebral palsy by degree of handicap, so a stu dy's diagnosis of cerebral palsy was accepted. Figures fro m the Collaborative Perinatal Project were included to provide comparisons and becaus e that study constituted a large and essentially singular United States cerebral palsy incidence study. The figures from th e Collaborative Perinatal Project included both infants who had a diagnosis of cerebral palsy who had died and cases of cerebral palsy th at the y defined as mild (not requiring bracing, wheelchair, etc .)" because we decided th at their "mild" category would be included in alI cases of cerebra l palsy in other studies. We primarily used later published reports abou t the ColIaborative Perinat al Project because thes e categories were included. Earlier reports that excluded de aths and "mild" cerebral palsy yielded a 2.5 per 1000 rate." For types of cerebral palsy, the denominator is alI cases of cerebral palsy. When discussing the different types of cerebral palsy, th e most frequently used categories of cerebral palsy included diplegia (or paraplegia), a form of cerebral palsy where the legs are pri maril y affected ; hemiplegia, where onl y one side of the body is affected ; and quadriplegia (or tetraplegia), where three or all four limbs are affected . Extrapyramidal (or dyskinetic) cerebral palsy, including choreoathetotic and dysto nic and ataxia, was included as much as possib le whe n stu dies had th is as a distinct category.
The anal yses of cerebral palsy by birth weight were done with live births at that birth weight as denominators . Because studies used either cerebral pals y or mental retardation as starting points, both types of stud ies were considered. Howe ver , when considering studies using mental retardation as the starting point, th e primary focus was that proportion of the mentally retarded who also had cerebral palsy. Mental retardation not associated with cerebral palsy was not reviewed. Results
Excluding cases that had an obvious postnatal origin, 10 studies published since 1980 determined the cumu lative incidence rates for cerebral palsy,,"'-17 (Table I). The average cumulative incidence rate of these studies was 2.7 per 1000 livebirths. Table II describes studies that included the breakdown by type of cerebral palsy.B,9,I[.l3,17-19Years of birth, not publication, are given. Not alI the previously discussed studies were included, because not all had breakdown by type of cerebral palsy. The avera ge proportion s of the different types of cerebral palsy of all with cerebral palsy were 34% diplegia, 30 % hemiplegia, 20 % qu adriplegia, and 16% extrap yramidal. Table III includes studies that grouped cerebral palsy by birth weight." 4, s, H-17, 20 Years of birth, rather than dates of publication, are indicated for the reasons previously stated. The average pr op ortions of cerebral palsy by birth weight of all children with cerebral palsy were 36% for those weighing 2499 gm . Some of these studies an alyzed cerebral palsy rates by smaller increments of birth weight" [I , [ 3 , 14 , [6 , [ 7 (Table IV) . The increments varied too much to do an exact comparison, but the figures are helpful to determine any trends in the incidence by birth weight.
Incidence of cerebral palsy 419
Volume 167 Number 2
Table II. Distribution of cerebral palsy by type* Study
Nelson and Ellenberg"] Pharoah et aLI7 Dowding and Barry" Dale and Stanley'? Riikonen et al. 15 Hagberg et al. 11 Jarvis et al." Composite rates
Country
1959-1966 1984 1979-1981 1971-1975 1978-1982 1979-1982 1972-1975
United States England Ireland Australia Finland Sweden England
Hemiplegia (%)
Quadriplegia (%)
Extrapyramidal (%)
29 40 25 22 29 36 29 30
24 27 10 32 3:j: 7:j: 39 20
14 11 27 5 24 15 9 16
32 24 38 39 44 41 l8§ 34
*Denominators are all cases of cerebral palsy. Rows may not total 100% because some types of cerebral palsy were excluded. tBased on survivors. :j:Used term tetraplegia. §Used term paraplegia.
Table III. Distribution of cerebral palsy by birth weight* Country
2499 gm (%)
Overalliow-birth-weight births (%)
United Statest England West Australia Denmark England Norway Sweden Ireland Finland Japan California
33 47 32 40 26 27 38 32 52 52 17 36
67 53 68 60 74 73 62 68 49 48 83 64
9.2 6.7
Study
Nelson and Ellenberg" Pharoah et aLI7 Stanley and Watsonl 4 Holst et aLI2 Jarvis et al. 9 Meberg'"
Hagberg et al. II Dowding and Barry" Riikonen et al. 15 Saito et aL20 Torfs et al." Composite rates
1959-1966 1984 1979-1981 1978 1972-1975 1980-1984 1979-1982 1979-1981 1978-1982 1963-1976 1959-1966
4.1:j:
3.5
7.0 4.2 4.0 5.1 4.0 4.5 6.8 5.3
*Denominator is cases of cerebral palsy. tCollaborative Perinatal Project. :j:Figure from Dale et al, 19 Some studies analyzed trends of cumulative incidences of cerebral palsy over periods of time"!': 13-17. 19 (Fig. 1). Some studies found recent minor decreases, others found almost no change in rate, and other studies found recent minor increases. When there was a minor increase, the type of cerebral palsy that increased the most was diplegia or cerebral palsy among lowbirth-weight (LBW) infants. A few studies analyzed the occurrence of serious mental retardation among children with cerebral palsy. Table V provides the figures from those studies. 18.21. 22 The average rate of serious mental retardation (IQ
