The mean body weights of premature infants at 4, 8, 12, and 18 months of corrected age were included within the 10th to 90th percentiles on the Korean children and adolescents' growth standard chart (2007). According to our investigation, 18.9% of the premature infants failed to catch up growing of body weight at 18 months of corrected age. Catch up growth failure rate was different by birth weight. In ELBW infant, 54.5% was failed to catch up weight while the rates were reported 30.0% and 9.4% in the infants whose birth weights were in the range of 1,000 to 1,499 g and 1,500 to 2,499 g. In other words, as birth weight decreased, catch-up growth failure rates increased. Compared to a study by Park et al.4)
, who insisted that 49.2% of ELBW babies failed to catch up growth until 12 months of corrected age, this study reached 66.7% in terms of catch-up growth failure rates. The time point at whichcatch-up growth is completed remains controversial, but many studies have agreed that it would not be completed until 2.5 to 3 years old. Therefore, it is necessary to perform an additional study on this matter over a longer period.
The results of this study in which catch-up growth failed in 42.9% of VLBW infants was higher than the catch-up growth failure rates (32.9%) until 24 months of corrected age in VLBW infants in a study by Ma et al.5)
. In this study, the ratio of ELBW to VLBW was as high as 52.3%, much far higher than the figure (30.2%) reported by Ma et al.5)
. According to a study by Lim et al.6)
, the catch-up growth failure rates until 18 months of corrected age reached 12.4%. Because the catch-up success criterion ofbody weight was based on whether the 3rd percentile was reached in the study by Ma et al.5)
, it cannot be directly compared to our observation. The catch-up growth failure rates at 18 months of corrected age in ELBW infants in this study were similar to the rates mentioned in other studies such as a study by Jeon et al.7)
. However, it is difficult to compare catch-up growth because there are a variety of factors that have an effect on growth after discharge from the hospital, such as gestational age, birth weight, number of days hospitalized in the NICU, ratio of intrauterine growth retardation, and newborn morbidity.
Catch-up growth failure is more common in SGA infants than in AGA babies8)
. In this study as well, 75.0% failed to catch up growth at 18 months of corrected age among the SGA infants, statistically significant compared to the failure rates (12.3%) in AGA infants.
According to one study, growth failure in VLBW infants has a negative effect on neurodevelopmental outcomes9)
. In this study, frequencies of abnormal neurological status at 4, 8, 12, and 18 months of corrected age in infant who failed weight catch-up were 12.5%, 31.3%, 19.0%, and 21.4%, respectively. The figures were significantly higher than the neurological deficit frequencies (6.8%, 13.6%, 7.8%, and 6.7% at 4, 8, 12, and 18 months of corrected age, respectively) in premature infants who have had successful catch-up growth of weight. Meanwhile, according to a study by Ma et al.5)
, there were fewer VLBW infants who failed to catch up growth until 24 months of corrected age than VLBW babies who succeeded to catch-up growth in terms of the Psychomotor Developmental Index. However, the differences were not statistically significant. Even though an additional study needs to be conducted with more cases, appropriate nutritional evaluation and active nutritional care are important in the prevention or solving of growth failure among premature infants who received an intensive care.
In this study, the body weight of 18.9% and 15.4% of infants at 4 and 8 months of corrected age, respectively, exceeded the 90th percentile. Since 12 months of corrected age, this kind of overweight frequency remained at 5 to 7%. Unlike parents' great concerns about growth failure, however, most parents were not concerned about overweightness of their premature infants. According to recent studies, rapid catch-up growth in the early stage could cause obesity, heart disease, and kidney disease10
. Therefore, it is important to carefully watch overweightness as well as growth failure. It is also required to perform a study on how fast catch-up growth should proceed in premature infants after NICU discharge. At the same time, it is necessary to check nutritional guidelines for premature infants.
The mean head circumferences of premature infants at 4, 8, 12, and 18 months of corrected age were included within the 10th to 90th percentiles on the Korean children and adolescents' growth standard chart (2007). The ratio of premature infants who failed to catch up growth in head circumference at 18 months of corrected age reached 10%. Among infants with head circumference <10th percentile, neurological deficits were observed in 29.5%, while developmental delay was found in 40.9%. Among infants with normal head circumference, on the contrary, neurological deficit was observed in 8.7%, while developmental delay was found in 10.9%. In addition, poor neurodevelopmental outcomes were observed among the infants who failed to catch up growth in head circumference due to frequent neurodevelopmental disorders. This kind of result is the same as the results of other papers in which catch-up growth in head circumference is was closely related with neurodevelopmental outcomes14
As mentioned above, it is important to check infant's growth in terms of body weight and head circumference. Therefore, this process must be included in observation at each visit to neonatal follow-up clinic.
The mean length of premature infants at 4, 8, 12, and 18 months of corrected age were included within the 10th to 90th percentiles on the Korean children and adolescents' growth standard chart (2007). However, catch-up growth failure rates of length were 20.5%, 24.0 %, 29.4%, and 12.2% at 4, 8, 12, and 18 months of corrected age, respectively. According to a study by Wit et al.18)
, about 10% of premature infants stay in the low length category at age 5. In this study, 12.2 % of premature infants stayed at length <10th percentile at 18 months of corrected age. In SGA infants, the catch-up growth failure rates at 18 months of corrected age reached 37.5%, which was higher than the failure rate (17.5%) until age 2 reported by Hokken-Koelega et al.19)
Studies about neurodevelopmental outcome of premature infants are mainly observation for major neurodevelopmental disabilities such as moderate to severe mental retardation, sensory impairment (hearing loss, vision loss), cerebral palsy, and seizure disorder. Major neurodevelopmental deficits account for 6 to 8% in LBW infants (birth weight<2,500 g), 14 to 17% in VLBW babies, and 20 to 25% in ELBW infants showing the evidence of increasing the major disabilities as birth weight decrease20
. According to a study by Choi et al.23)
, 8.5% of VLBW infants and 19.2% of ELBW babies had cerebral palsy. Sensory nerve impairment, seizures, and hydrocephalus with a ventriculoperitoneal shunt have not been categorized as major neurological disabilities and not included in his study. According to a study by Jeon et al.7)
, ELBW infants' survival rates have improved since 2000. At the same time, the incidence rate of cerebral palsy until 18 months of corrected age decreased from 22.2 to 8.2%. In this study, major disabilities accounted for 11%, higher than the incidence rate of major disabilities among general LBW infants (6 to 8%). Among 120 VLBW infants, 31 babies were suffering from a major neurological deficit. Specifically, a major disability was detected in 18 (39.1%) among 48 ELBW infants and 13 (17.6%) among 74 infants with birth weight 1,000 to 1,499 g. In other words, the incidence rate of major disabilities increased as birth weight decreased. In general, neurological deficit was directly related with perinatal problems24
. In this study, however, risk factors during the perinatal period were not analyzed. Hence, it was impossible to determine the effect of other risk factors such as increases in the incidence of neurological deficits.
In addition, the proportion of premature infants categorized as 'suspect' with abnormal muscle tone (e.g., transient dystonia) and a problem in posture or reflex reached 6.7%. Among the premature infants, the incidence rate of dystonia was the highest (21 to 36%) at 7 months of corrected age27
. In this study, the frequency of dystonia was the highest (12.5%) at 8 months of corrected age. However, the figure was lower than the level reported in earlier studies. It appears that this disparity occurred due to differences in gestational age, birth weight, and neonatal morbidity. A further study needs to be performed on various risk factors to elucidate this point.
According to meta-analysis, the intelligence quotients (IQs) of LBW infants were usually lower than those of normal babies by 5 to 7 points29)
. In comparison, except for severe disorders, the IQ scores of premature infants were lower than those of normal babies by 3.8 to 9.8 points. The difference was reported to be up to 12 to 17 points in some studies30
. In general, the IQ scores of the VLBW infants were lower than those of full-term infants by 8 to 11 points30
. In this study, it was impossible to perform an IQ test on premature infants until 18 months of corrected age. However, 14.4% of premature infants categorized as having a developmental delay had developmental quotient (DQ) scores below mean -1 SD. No large difference was observed from 8 to 18 months of corrected age, and developmental delay rates stayed at about 20%. Because it is hard to predict IQ during the prepubertal period using the Bayley Scales of Infant Development17)
, it is unlikely that the DQ examined until 1s8 months of corrected age reflects the level of future cognitive development. In terms of the characteristics of cognitive development, because other factors such as nutrition and environment are influential as well, it is necessary to observe infants over a longer period.
In Korea, no earlier study has examined parental concerns about their premature infants after NICU discharge. In this study, 27.9% of parents worried about the development of their premature baby. Therefore, it is necessary to educate and teach them how to care for their premature baby after NICU discharge. Until 8 months of corrected age, their concerns were mostly about motor development. Concerns about cognitive, sensory and language development were observed since 12 months of corrected age. In particular, the results of this study, which focused on the infants up to 18 months of corrected age, show that it is necessary to teach parents to consider their infant's corrected age with guidance in the follow-up clinic.
Regarding nutrition and eating problems, 15.9% showed concerns. Specifically, they worried about inadequate eating and gastrointestinal functions at 4 months of corrected age, weaning food and gastrointestinal functions at 8 months of corrected age, no progress in weaning to food at 12 months of corrected age, and poor oral intake and failure to weaning to food at 18 months of corrected age. In particular, gastrointestinal problems such as indigestion, loose stools, frequent stool passage, constipation, and vomiting almost disappear at 8 months of corrected age. It is desirable to teach parents and guide them to consider their biggest concerns at each stage when they visit the follow-up clinic. If parents worry about poor food intake even though their child's growth is normal, in particular, it is necessary to evaluate growth based on corrected age and let them know the results of the evaluation.
In terms of parents' concerns about their premature infants' growth, no difference was observed by corrected age. They were mostly concerned about low weight and slow weight increases. While 10 to 12% of parents were concerned about growth failure, almost no parents worried about overweight. This kind of result is very particular because the overweight infants (body weight>90th percentile) exceeded 15% up to 8 months of corrected age and 5 to 7% of whom had it at12 and 18 months of corrected age. Since the rapid catch-up growth in LBW infants could cause adult diseases such as obesity, heart disease, and kidney disease10
, it is necessary to teach parents how to control rapid weight increases (e.g., nutrition, and breast feeding guidelines) in an early stage after NICU discharge.
In this study, the parental concerns about developmental delay until 18 months of corrected age after NICU discharge had 57.1% sensitivity and 77.0% specificity. Concerns about growth failure in body weight and length had <10% sensitivity and >90% specificity. On the contrary, concerns about overweight had 8.2% sensitivity and 100% specificity. This kind of result differs from those of a study by Jensen and Harper34)
, who insisted that parental concerns about development, social skills, and disease of their high-risk child at age 5 were well matched with the developmental status of their infant. It has been impossible to figure out how this kind of difference has occurred. This study has attempted to point out that it is important to monitor and evaluate the development and growth of a child based on the standardized and objective evaluation tools by age instead of approaching the matter with parental complaints only.
Regarding disease contraction after NICU discharge, the diseases treated at 4, 8, 12, and 18 months of corrected age were examined. According to the investigation, about 30% of premature infants suffered from an infectious disease (mostly upper and lower respiratory tract infections). In addition, iron deficiency anemia was observed in 5 to 7% of infants. In this study, however, hemoglobin and iron status and iron replacement therapy were not analyzed. Therefore, it was impossible to determine how much iron deficiency anemia was actually present. This study confirmed that it is essential to carefully watch respiratory infections as well as development, growth, and nutrition in the health management of premature infants after NICU discharge.