Abstract
[Purpose] To determine the age in months of bilateral hand use during the infancy period of preterm infants with birth weight <1,500 g. [Participants and Methods] This retrospective, observational study included 57 infants with no neurodevelopmental handicaps (average weight at birth 963.2 ± 298.2 g, gestational age 28.4 ± 3.1 weeks), who were transferred to the neonatal intensive care unit at a medical center in Japan between 2010 and 2014. The patients were classified into two groups based on weight at birth: 32 infants with birth weights <1,000 g (Group A) and 25 with birth weights between 1,000 and 1,499 g (Group B). Data on the ages at which bilateral hand use was attained (“playing with both hands together”, “transferring a toy between the two hands”, and “grasping two toys, one in each hand”) were collected from the respective medical records and compared between the two groups. [Results] Significantly delayed bilateral hand use was detected in Group A compared to that in Group B for “transferring a toy between the two hands” (90th percentile, 7.2 months compared to 6.3 months). For the other two items, no differences were detected between the two groups. [Conclusion] The development of bilateral hand use during infancy differed among infants with very low birth weight and was delayed in the group with a lighter birth weight group.
Keywords: Bilateral hand use, Infancy, Very low birth weight
INTRODUCTION
Neonatal care in Japan is among the best in the world, and the neonatal mortality rate is on the decline1, 2). However, the number of preterm infants remains high3, 4). Low birth weight infants with preterm birth or restricted fetal growth have poorer developmental prognoses than full-term infants5). In particular, infants with very low birth weight (VLBW), classified as those weighing <1,500 g, often have a poor developmental prognosis6). VLBW infants show delayed overall motor development even when no neurological abnormalities are observed7, 8). Delays in fine motor function have long-term effects on school age and adulthood and may interfere with daily life and employment7).
Several studies have reported on fine motor function in VLBW infants from school age onward, but few have described fine motor function status in early infancy7, 9). An essential early stage in the development of fine motor functions involves bilateral hand use during infancy. This involves using both hands to grasp and manipulate objects. During this stage, infants begin by bringing their hands together at the midline and develop the ability to grasp and transfer objects from one hand to the other hand. VLBW infants may have delayed development of bilateral hand use in the midline due to infants’ being premature as well as prolonged hospitalization and treatment in the neonatal intensive care unit (NICU).
Previously, we investigated grasping of one hand in VLBW infants and found that infants with a birth weight of less than 1,000 g had delayed acquisition of one-handed grasping movements10). We then conducted a long-term study of subsequent upper limb function. The present study aimed to determine the age in months of bilateral hand use achievement in VLBW infants based on weight at birth.
PARTICIPANTS AND METHODS
This single-center, retrospective, observational study assessed a total of 104 VLBW infants admitted to the NICU of a university hospital in Japan between 2011 and 2014. The criteria for exclusion included 1) death; 2) prolonged hospitalization due to surgical procedures; 3) diagnosis of cerebral palsy, chromosome abnormalities, malformation syndromes, or neurological disorders; and 4) infants who were not followed up as outpatients because of transfer or relocation prior to the completion of all evaluations. After exclusion of 47 of the 104 infants, 57 (mean birth weight 963.2 ± 298.2, gestational age 28.4 ± 3.1 weeks) were included. To evaluate bilateral hand use achievement in VLBW infants by weight at birth, they were divided into the following two groups: birth weight <1,000 g (Group A) (n=32) and birth weight 1,000–1,499 g (Group B) (n=25). Participants’ perinatal data were collected. The participants’ characteristics are shown in Table 1.
Table 1. Characteristics of very low birth weight infants according to weight at birth.
| Birth weight | ||
| Group A (<1,000 g) | Group B (1,000–1,499 g) | |
| n=32 | n=25 | |
| Multiple birth, n (%) | 9 (28.1) | 8 (32.0) |
| Male, n (%) | 17 (53.1) | 12 (48.0) |
| Weight at birth, g | 734.0 ± 150.7 | 1,256.6 ± 135.7* |
| Gestational age, weeks | 26.9 ± 2.7 | 30.4 ± 2.3* |
| Small for gestational age, n (%) | 16 (50.0) | 6 (24.0)† |
| Apgar score 1 min | 4.0 ± 2.5 | 6.7 ± 1.6* |
| Apgar score 5 min | 6.2 ± 2.0 | 8.2 ± 1.0* |
| Intraventricular hemorrhage | ||
| Normal, n (%) | 27 (84.4) | 21 (84.0) |
| Grade 1–2, n (%) | 4 (12.5) | 4 (16.0) |
| Grade 3–4, n (%) | 1 (3.1) | 0 (0) |
| Periventricular echo densities | ||
| Normal, n (%) | 24 (75.0) | 20 (80.0) |
| Grade 1, n (%) | 7 (21.9) | 5 (20.0) |
| Grade 2–3, n (%) | 1 (3.1) | 0 (0) |
| Periventricular leukomalacia, n (%) | 0 (0) | 0 (0) |
| Retinopathy of prematurity, n (%)* | ||
| Normal, n (%) | 16 (50.0) | 18 (72.0) |
| Grade 1–2, n (%) | 8 (25.0) | 6 (24.0) |
| Grade 3–5, n (%) | 8 (25.0) | 1 (4.0) |
| Days of ventilation, days | 30.2 ± 22.6 | 4.8 ± 7.2* |
| Respiratory distress syndrome, n (%) | 21 (65.6) | 6 (24.0)† |
| Chronic lung disease, n (%) | 26 (81.3) | 9 (36.0)† |
| Septicemia in hospital admission, n (%) | 7 (21.9) | 1 (4.0) |
| Symptomatic patent ductus arteriosus, n (%) | 8 (25.0) | 4 (16.0) |
| Patent ductus arteriosus ligation, n (%) | 3 (9.4) | 0 (0) |
*p<0.05: unpaired t-tests, †p<0.05: χ2 tests.
The ages at bilateral hand-use achievement were analyzed from patients’ records. In this medical center, VLBW infants undergo ongoing follow-up care in the developmental outpatient department after discharge from the NICU. The timing of the acquisition of bilateral hand use was evaluated by a physical therapist in our rehabilitation room at the developmental outpatient department every month, and the day of achievement was adjusted to the corrected age. Bilateral hand use included the following three early-stage items according to the criteria of the Munich Functional Development Diagnostic11): “Playing with both hands together”, “Transferring a toy between the two hands”, and “Grasping two toys, one in each hand”. The toy was a wooden cube block with a ridge length of 3 cm.
Unpaired t-tests, χ2 tests and Wilcoxon rank sum tests were conducted to compare characteristics between groups. The Wilcoxon rank sum test was employed to compare the ages at the time of bilateral hand use achievement between the groups. The distribution of age in months of bilateral hand use achievement was calculated using Kaplan–Meier estimation and analyzed with the log rank test. SPSS version 28 was used for statistical analysis. The level of significance was set at <5%.
This survey was approved by the research ethics committee of the first author’s institution (approval number: 5498). An opt-out system was adopted for the disclosure of this research information, and the right to veto was guaranteed.
RESULTS
The percentile values for the acquisition of bilateral hand use by birth weight are shown in Table 2. The time of “Transferring a toy between the two hands” attainment was considerably later in the group A than in the group B (p=0.01). No considerable differences were observed in acquisition time for “Playing with both hands together” and “Grasping two toys, one in each hand” between the groups. The Kaplan‒Meier plots of the age range of bilateral hand use attainment by birth weight demonstrate that the group A showed slower achievements than the group B in “Transferring a toy between the two hands” (p=0.046) (Fig. 1). Considering “Playing with both hands together” and “Grasping two toys, one in each hand”, no difference was observed in achievement between the two groups.
Table 2. Age at bilateral hand use achievement in very low birth weight infants according to weight at birth (months).
| Birth weight | ||
| Group A (<1,000 g) | Group B (1,000–1,499 g) | |
| n=32 | n=25 | |
| Playing with both hands together | ||
| 10 percentiles | 3.2 | 3.1 |
| 50 percentiles | 4.0 | 3.7 |
| 90 percentiles | 4.9 | 5.3 |
| Transferring a toy between the two hands* | ||
| 10 percentiles | 5.6 | 5.0 |
| 50 percentiles | 6.4 | 5.8 |
| 90 percentiles | 7.2 | 6.8 |
| Grasping two toys, one in each hand | ||
| 10 percentiles | 6.4 | 5.8 |
| 50 percentiles | 8.0 | 7.3 |
| 90 percentiles | 9.9 | 9.9 |
*p<0.05: Wilcoxon rank sum test.
Fig. 1.
Kaplan‒Meier survival plots for age of bilateral hand-use achievement for infants with very low birth weight according to weight at birth.
DISCUSSION
This study examined the bilateral hand-use age of achievement in infants with VLBW stratified by weight at birth. We found that the group A (lighter birth weight group) of VLBW infants were more delayed in acquiring bilateral hand use to transfer a toy between two hands.
A previous study on young adults born preterm showed that those experienced VLBW exhibited reduced fine and gross motor abilities compared to controls12). VLBW infants were shown to be unable to overcome motor problems when they reached adulthood. Furthermore, a study of 6–7-year-old children born preterm showed that VLBW children scored significantly lower in most written tasks and also took longer to complete these tasks13). Thus, previous studies have shown that VLBW children have poorer fine motor function, but the age of investigation was usually school age or later. The present study showed the timing of acquisition of fine motor function during infancy in VLBW children was deferent according to birth weight. Specially, the acquisition of “Transferring a toy between the two hands” was delayed more in the group A (lighter birth weight group) of VLBW infants than the group B.
“Transferring a toy between the two hands” requires coordinated action. Once the hand receiving the toy grasps it, the hand giving it must let it go. Thus, both hands must simultaneously perform two different functions11). Preterm infants with lighter birth weights have been reported to have poorer hand coordination14, 15), and the results of this study supported the results of those previous studies.
The results of this research are significant because they allow medical staff to refer to the time of acquisition of bilateral hand use for each infant’s birth weight and to follow up on their development. Early developmental support, such as sensory-motor experiences, in the NICU may facilitate hand coordination in light birth weight infants. This study has demonstrated the time of acquisition of hand-grasping movements in VLBW infants with no neurodevelopmental handicaps by weight at birth, which is an important indicator to determine whether infants who deviate significantly from this time are at risk for developmental delays.
Our study had some limitations. First, the timing of functional acquisition in all infants included the effects of physical therapist’ developmental support interventions to promote motor development. Second, the number of patients was small. Further studies, including larger numbers and a multicenter study design, are needed.
In conclusion, the transfer of toys between the two hands in infants with VLBW was delayed with lighter birth weight.
Conflicts of interest
The authors declare no conflict of interest.
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