| | Inter- and intra-modal matching in very low birth weight and small for gestational age adolescents☆Accepted 23 March 2006. Abstract BackgroundMotor problems in low birth weight children may be related to problems in sensorimotor integration processes. Specific tests of inter- and intra-modal matching have not been used in low birth weight populations. AimExamine whether low birth weight adolescents have poorer performance in inter- and intra-modal matching than normal birth weight adolescents. Study designA population based follow up study of very low birth weight and small for gestational age children at 14 years of age. Outcome measuresInter- and intra-modal matching was assessed by a manual matching task and results were presented for the preferred and the non-preferred hand in the visual (inter-modal) and proprioceptive (intra-modal) condition. ResultsVLBW adolescents performed poorer in inter- and intra-modal matching compared with the reference group. However, the results were mainly due to a higher number of adolescents with cerebral palsy (CP) and a low estimated intelligence quotient (IQest) in the VLBW group. SGA adolescents showed poorer performance with their non-preferred hand compared with their preferred hand in both inter- and intra-modal matching, whereas adolescents in the reference group and VLBW adolescents with normal IQest and without CP performed equally well with both hands. ConclusionVLBW adolescents with normal IQest and without CP do not have major problems in inter- and intra-modal matching. The poorer performance with the non-preferred hand in the SGA group may suggest a specific effect of intrauterine growth retardation. 1. Introduction  Prematurity and intrauterine growth restriction both represent risk factors for motor problems. Several studies have reported increased prevalence of motor problems in children with birth weight below 1500 g (very low birth weight: VLBW) at preschool [1], [2], [3], [4] and school age [5], [6], [7], [8], [9]. We have previously reported that VLBW adolescents have increased risk of motor problems both in manual dexterity, ball skills and balance compared with a reference group [10]. Children who have been growth retarded in utero are usually diagnosed by having a low birth weight for their gestational age (small for gestational age: SGA). Studies on motor problems among younger SGA children born at term have shown inconsistent results [11], [12], [13]. We found that SGA adolescents, particularly boys, had increased risk of motor problems in manual dexterity [10]. Motor problems in children with low birth weight may be related to problems in sensorimotor integration processes. Such processes may involve different sensoric modalities and include transfer of information from one hemisphere to the other. It has been widely reported that low birth weight children also have problems related to visuo-motor functions [5], [14], [15], [16], [17], [18], [19], [20] which could in part explain the motor problems in these children. A specific test matching vision with proprioception (inter-modal matching) and the proprioceptive space of one hand with the proprioceptive space of the other (intra-modal matching) has been developed [21]. Associations between poor inter- and intra-modal matching and increased risk of motor problems in children in normal populations have been reported [22], [23], [24], [25], [26]. Although both VLBW and SGA children are at increased risk of having motor problems, inter- and intra-modal matching have not been examined in these risk groups. Moreover, in low birth weight children tests of inter- and intra-modal matching may be particularly relevant since studies using magnetic resonance imaging (MRI) have reported a higher prevalence of ventricular dilatation [27], [28], [29], [30], [31], [32], [33], white matter reduction [29], [30], [31], thinning of corpus callosum [28], [30], [31], [32] and periventricular gliosis/leukomalacia [27], [29], [30], [32] in VLBW than in normal birth weight children and adolescents. Thus, the aim of this study was to examine whether low birth weight adolescents have poorer performance in inter- and intra-modal matching than adolescents with appropriate birth weight, assessed by a manual matching task. 2. Method 2.1. Study design The study is a population based follow up study of two groups of adolescents with low birth weight; one group of preterm very low birth weight (VLBW) adolescents and one group of term small for gestational age (SGA) adolescents. The groups are being compared with a reference group of normal birth weight. The VLBW adolescents were born to mothers living in the two counties of North- and South-Trøndelag (total population approximately 375,000) and admitted to the Neonatal Intensive Care Unit (NICU) at the University Hospital in Trondheim (the referral hospital) between January 1986 and December 1988. Children born in 1988 were assessed thoroughly at one and six years of age [27], [34]. The SGA and reference adolescents were born to mothers living in the Trondheim region (total population approximately 135,000). They were enrolled before week 20 of pregnancy in a multicenter study between January 1986 and March 1988 [35], [36]. A 10% random sample of women (para 1 and 2) was selected for follow up during pregnancy. At birth, all children born to mothers in the random sample and all the SGA children were included for follow up. The children were examined by project paediatricians at one and five years of age [37]. The present follow up study was carried out from November 2000 to October 2002, when the children were 14 years old, as part of a larger study. The follow up examination included assessment of motor and intellectual abilities, in addition to neuropediatric and psychiatric evaluation. 2.2. Study population 2.2.1. VLBW adolescents Ninety-nine children with a birth weight ≤ 1500 g were admitted to the NICU in 1986–1988. Of these children, 23 died, one child with trisomi 21 was excluded, and six had moved out of the region. Of the remaining 69 children, 15 (22%) did not consent to participate and one child with CP (quadriplegia) was not able to do the test. Thus, a total of 53 VLBW children (29 boys and 24 girls) were examined. In the VLBW group, 19 adolescents were born SGA, whereas 34 were born non-SGA, according to Norwegian standards [38]. However, we have treated them as one group since there were no differences between SGA and non-SGA VLBW adolescents on any of the inter- or intra-modal matching tests. 2.2.2. SGA adolescents Of 1200 eligible women, 104 (8.7%) gave birth to a SGA child, defined by a birth weight <10th centile, adjusted for gestational age, gender and parity. At follow-up, 12 children had moved. Of the remaining children, 33 (36%) did not consent to participate, leaving 59 SGA children (27 boys and 32 girls) for further examination. 2.2.3. Non-SGA adolescents The reference group comprised 120 children with birth weight ≥10th centile for gestational age, born at term to mothers in the 10% random sample. Ten children had moved, while 28 (25%) did not consent. In total, 82 children in the reference group (35 boys and 47 girls) were examined. 2.3. Methods Each adolescent was tested with a manual matching task according to von Hofsten and Rösblad [21]. This manual matching task has been used in different age groups and populations [21], [22], [23], [24]. The manual matching task uses a test board measuring 60×80 cm. The task is to match pins from underneath the test board to targets at the top of the board. Two different conditions to locate the target were examined; one when the target is seen (Fig. 1A: Inter-modal matching; matching of vision and proprioception) and one when the target is felt (Fig. 1B: Intra-modal matching; matching of the proprioceptive space of one hand with the proprioceptive space of the other). The subjects had four attempts with each hand (preferred and non-preferred hand) in each condition. X- and y-coordinates were used to measure the distance between the pin position and the target. Absolute error (a), the distance in mm between the pin (p) and the target (T), was calculated according to the equation  . Mean absolute error was calculated as the sum of the absolute errors over the four trials (a1−a4) divided by four  . The systematic error (s) reflects a systematic shift between the system (visual or proprioceptive) that indicates the position of the target and the proprioceptive system of the matching arm [21]. The systematic error is the distance between the centre of the four pin positions (Pc) and the target (T) (Fig. 2). The coordinates of Pc are calculated by the mean position in the x- and y-directions. The systematic error is calculated by the formula  . The random error (r) reflects the level of precision in pointing [21], and is the distance between the pin position (p) to the centre of pin positions (Pc) (Fig. 2). The mean random error is calculated as the sum of the random errors over the four trials (r1−r4) divided by four  . Mean directional error was calculated for the horizontal and vertical direction as the mean of the distance between the four pin positions and the target in x- and y-directions separately. All tests were performed by the first author, who was blinded to group assignment. Cerebral palsy (CP) was diagnosed and classified as diplegia, hemiplegia and quadriplegia by project paediatricians [39]. An estimate of intelligence quotient (IQest) was calculated using the vocabulary, arithmetic, block design and picture arrangement subscales of Wechsler Intelligence Scales (WISC-III) [40], [41]. We defined “low IQest” below 2 SD of the reference group mean value. Socioeconomic status (SES) was calculated according to Hollingshead's Two Factor Index of Social Position [42]. 2.4. Ethics The Regional Committee for Medical Research Ethics approved the study protocol. Written informed consent was obtained from both adolescents and parents. 2.5. Statistical analysis SPSS for windows version 12.0.1 (SPSS Inc, Chicago, IL) was used for data analysis, and a significance level of 0.05 was chosen. Two-group comparisons were made by Student's t-test for variables with a normal distribution and Mann–Whitney U-test for variables with a non-normal distribution. The χ2 test was used to analyse differences in proportions between groups. Absolute, systematic and random errors were log normal, thus geometric means with 95% confidence intervals are presented for these variables. We used parametric methods on the log transformed data. With a power of 80% (β=0.20) and α=0.05, this study may detect a 3.8 mm difference in mean absolute error in the visual condition (preferred hand) and a 5.7 mm difference in the proprioceptive condition (preferred hand) between the VLBW and the reference group. 4. Discussion In this study, we found that VLBW adolescents performed poorer in inter- and intra-modal matching compared with a reference group. However, the results were mainly explained by a higher number of adolescents with CP and low IQest in the VLBW group. SGA adolescents showed poorer performance with their non-preferred hand compared with their preferred hand in both inter- and intra-modal matching, whereas adolescents in the reference group and VLBW adolescents with normal IQest and without CP performed equally well with both hands. We are not aware of other studies that have used the manual matching task in low birth weight populations. The 10th centile definition of SGA is crude, and a certain proportion of normal small infants could have been classified as SGA, whereas some infants who may have been growth retarded in utero, could have been classified as belonging to the reference group. This may have contributed to an underestimation of potential differences between SGA and reference adolescents. The VLBW adolescents were classified according to a birth weight ≤1500 g. In the VLBW group, 36% were born SGA. However, there were no differences in inter- and intra-modal matching between SGA and non-SGA VLBW adolescents, and we have therefore chosen to treat them as one group, as a contrast to the adolescents born at term. The reason why 76 adolescents (28%) did not want to participate in this study is not known. We found, however, no significant differences in key variables between mothers and children who participated and those who did not consent to participate. It is therefore unlikely that the results are due to selection bias. The examiner was blinded to the adolescents' group assignment, thus, it is unlikely that there is information bias. The only finding in the inter-modal matching condition (i.e. matching of vision and proprioception) was higher random errors in the VLBW group, which may imply a slight deficit in the transfer between visual input and motor output, leading to less precise matching. This may be consistent with the finding of reduced visuo-motor integration in VLBW children [5], [14], [15], [16], [17], [18], [19], [20]. In the intra-modal matching condition (i.e. matching of the proprioceptive space of one hand with the proprioceptive space of the other), the VLBW group demonstrated poorer performance with the non-preferred hand than the reference group in terms of higher mean absolute and random errors. However, these results were no longer statistically significant when we excluded subjects with CP and low IQest. Power analyses suggested that we were able to detect differences of approximately 5 mm between groups in both conditions. Smaller differences may be biologically interesting, but are less likely to be of major clinical importance. Compared with other known impairments in VLBW populations, both in motor abilities [1], [2], [3], [4], [5], [6], [7], [8], [9], [10] and in visuo-motor integration [5], [14], [15], [16], [17], [18], [19], [20], it may be somewhat surprising that the VLBW adolescents did not differ more from adolescents born at term on these tasks. This could suggest that the regions of the brain concerned with manual matching tasks are preserved in VLBW adolescents. One may also speculate whether other parts of the brain have adjusted their capacity in order to process such information adequately [43]. However, we discovered a difference in performance between hands in both the VLBW and the SGA group, but not in the reference group. The VLBW group had poorer performances with their non-preferred hand compared with their preferred hand in the intra-modal matching condition, reflected by higher mean absolute error and systematic error. There were no gender differences in this group, and the differences between hands disappeared when we excluded subjects with CP and low IQest. The SGA group had poorer performances with their non-preferred hand compared with their preferred hand in both inter- and intra-modal matching conditions (mean absolute error and systematic error), and these differences remained significant when we excluded subjects with CP and low IQest. The gender differences in the SGA group were striking; the boys seem to have poorer inter-modal matching with the non-preferred hand, which may imply a deficit in visual input and/or motor output in this hand. This may be in accordance with their poor manual dexterity on the Movement ABC [10]. For the SGA girls, the difference between hands seemed to manifest itself only in the intra-modal matching condition. Asymmetrical performances have also been found in studies on other groups of children with motor problems [22], [23], [24], [44]. Sigmundsson and Whiting [24] argue that these findings could be accounted for by insufficiency within the hemisphere controlling the non-preferred hand, with or without a dysfunctional corpus callosum. Our finding that this asymmetry was more evident in the SGA than in the VLBW group, may suggest a specific effect of intrauterine growth retardation. The reason why the asymmetry manifested itself differently in boys and girls cannot be answered in this study. 5. Conclusion VLBW adolescents with normal IQest and without CP do not seem to have major problems in inter- and intra-modal matching as assessed by the manual matching task. However, SGA adolescents performed poorer with their non-preferred than their preferred hand both in inter- and intra-modal matching. This asymmetry may be a part of the complex aetiology of motor problems in this group, and may be a specific effect of intrauterine growth retardation. 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a Department of Laboratory Medicine, Children's and Women's Health, Faculty of Medicine, Norway b Department of Sociology and Political Science, Faculty of Social Sciences and Technology Management, Norway c Department of Public Health and General Practice, Faculty of Medicine, Norway d Department of Neuroscience, Faculty of Medicine, Norway e Norwegian University of Science and Technology, Trondheim, Norway  Corresponding author. Department of Laboratory Medicine, Children's and Women's Health, St. Olavs Hospital HF, N-7006 Trondheim, Norway.
☆ ETHICS APPROVAL: The Regional Committee for Medical Research Ethics (Health Region IV) approved the protocol May 5th 2000. PII: S0378-3782(06)00112-5 doi:10.1016/j.earlhumdev.2006.03.015 © 2006 Elsevier Ireland Ltd. All rights reserved. | |
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