Is late walking a marker of morbidity? Steering Committee, Oxford Region Child Development Project.

Abstract

We identified 410 infants who were not walking independently by the age of 18 months from among a geographically defined population of 4275 infants who either were born weighing less than 2000 g or had needed admission to the special care nursery in the neonatal period. The outcome of the late walkers was ascertained at the age of 3 years by health visitors using a standard questionnaire. Of the late walkers, 230 (56%) had an associated abnormality diagnosed before the age of 3 years, and in 77 of these children (33%) this was definite or suspected cerebral palsy. The high prevalence of late walking among infants born before 28 weeks' gestation (46%) was almost entirely accounted for by a high incidence of impairment. Late walking is a simple marker of morbidity in this group of infants. Nearly every child (97%) can walk five steps independently by the age of 18 months.' Failure to achieve this milestone may be associated with neurological abnormality, or impairment in other systems, but in many late walkers there is no obvious cause. They could represent the limit of normal biological variation in the age of independent walking. Infants who have been born preterm are at increased risk of delayed motor development,2 and of motor impairment, particularly cerebral palsy.3 It is therefore likely that they are over-represented among the late walkers. We have studied the association between late walking, neurological and non-neurological abnormality, and gestational age at birth, to find out to what extent late walking can be used as a risk marker for impairment among low birthweight babies or in babies who have been ill during the neonatal period, and what the relative contributions are of 'biological immaturity' and impairment to late walking among babies born early in gestation. Subjects and methods We studied infants born in 1984 and 1985 whose mothers were resident in the Oxford health region at the time of delivery, and who either weighed less than 2000 g at birth, or were admitted to a special care nursery for more than 24 hours during the neonatal period. Those who survived were enrolled in the study. Eligible infants were identified by a weekly telephone call to each of the 10 special care nurseries in the region. Low birthweight infants born outside the region (to mothers normally resident in the region) were identified from birth registration data. Information on larger infants born outside the region who were in special care nurseries was obtained from health visitors. We sought parents' permission to send the results of a number of routine screening tests done at 7-8 months and 18 months to the project office.4 As each infant approached the age of 7-8 months and 18 months (uncorrected for gesta-tional age at birth), a form was sent to health visitors for completion at the time of assessment. The questions on the 18 month form included 'Is the child walking five steps independently?' For all the late walkers and also for those whose ability to walk at 18 months of age was not known, we found out the outcome at the age of 3 years by sending a simple questionnaire to the health visitors of the children who were not walking requesting information about the eventual age of walking, and about any abnormality that had been diagnosed. We classified the late walkers into one of six categories: cerebral palsy, other neurological disease, global delay, major congenital anomaly (not affecting the central nervous system), other diseases, and no detectable associated condition. If cerebral palsy was associated with other impairments, the child was classified as having cerebral palsy. Global delay was defined as delay in all fields of development. The cases of cerebral palsy on a regional register of impairment in 3 year old children were used to assess the predictive ability of failure to walk at the age of 18 months for cere-bral palsy.5 Results A total of 4527 infants were eligible for entry into the study. Sixty one died between the time of discharge from the special care nursery and the age of 18 months. The ability to walk at the age of 18 months was ascertained for 4275 of the remaining 4466 infants (96%). The mean (SD) birth weight (2584 (840) g) and mean gestational age (36-3 (3 5) weeks) of infants whose ability to walk was known were similar to those of babies whose ability was not known (birth weight 2611 (819) g, and gestational age 36-2 (3-3) weeks). At 18 months, 410 of 4275 of the children (10%) were not walking independently. 486