Introduction: Although there are several reports on the prevalence of underweight or obesity in low birth weight (LBW, <2.5 kg) children, there are few longitudinal studies from birth to early infancy. Methods: We enrolled 177 (93 boys) LBW and 2485 (1267 boys) normal birth weight (NBW, ≥2.5 and <4.0 kg) children. Height and weight data at birth and at 1.5, 3.5, and 5 years were obtained from mother-health child records. Underweight and obesity were defined as <5 th percentile and ≥90 th percentile of the body mass index (BMI), respectively, based on reference values for Japanese children. Results: LBW children had accelerated growth from birth to age 3.5 years, but at Age 5, both sexes had significantly lesser height and weight z-scores, with notably lesser BMI percentile scores for girls, compared with NBW children. The prevalence of underweight was significantly higher in the LBW children throughout the study period. There were no significant differences in the prevalence of obesity between the two groups, except for at birth. Multiple regression analysis revealed that small-for-gestational age was associated with underweight at Age 5 years. Conclusions: This study indicates that, up to Age 5, underweight is a more serious problem than obesity in LBW children. Our results suggest that careful observation of growth from early infancy is necessary to prevent the occurrence of underweight in early infancy.
Advances in perinatal care over the past two decades have reduced the mortality rate associated with very low birth weight (VLBW, <1.5 kg) [
After initial postnatal growth failure, most preterm infants exhibit catch-up growth in weight, height, and head circumference, generally starting early in the neonatal period and with catch-up occurring by early infancy [
A large body of reports exists on the association of LBW and postnatal growth in early infancy with later health consequences in adolescence or in adulthood [
Based on this knowledge, the present study aimed to follow-up the growth of LBW and normal birth weight (NBW, ≥2.5 and <4.0 kg) children from birth to 5 years of age, longitudinally. In addition to comparing the two groups, we aimed to determine the prevalence of both underweight and obesity in relation to the physical characteristics of LBW children at birth.
We retrospectively included 1635 patients admitted to the neonatal intensive care unit of the Nara Medical University Hospital, Nara, Japan, from 1994 to 2007. Current addresses were missing for 312 patients, and the birth weight of 675 patients were ≥2.5 kg. Consequently, we sent questionnaires to the parents of 648 children whose birth weight was <2.5 kg between September 2012 and December 2013, and 240 questionnaires (37.0%) were returned. We excluded the questionnaires for patients with cerebral palsy, trisomy 8 syndrome, and Diamond- Blackfan anemia and patients who received growth hormone. Therefore, a total of 177 children (93 boys, 84 girls) were enrolled. Perinatal and birth data were collected from medical charts, and values of height and weight from birth to 5 years of age were obtained from mother-health child records maintained by the mother.
This project was approved by the ethical and epidemiological committees of both the Nara Women’s University and Nara Medical University Hospital. In the questionnaire, we explained that parental consent was implied by completing and returning it.
We enrolled 2485 children (1267 boys, 1218 girls) aged 5 years old who were attending kindergarten or nursery school in the Nara Prefecture of Japan. Their birth weight was required to be ≥2.5 kg and <4.0 kg. The details of these participants and the method of data collection are available elsewhere [
Body mass index (BMI) was calculated as body weight in kilograms divided by height in meters squared (kg/m2). We defined underweight and obesity by the BMI as that less than the 5th percentile and that equal to or more than the 90th percentile, respectively, based on the standards of the Japanese Association for Human Auxology [
Differences by sex in the perinatal and birth data were examined by the Student t-test or Fisher exact test. The Student t-test was used to compare the physical characteristics from birth to Age 5 years between the LBW and NBW children. The prevalence of underweight and obesity in LBW and NBW children was compared by the Fisher exact test. Comparison of the physical characteristics of LBW children at birth for those who were underweight, normal weight, and obese at Age 5 was also made using the Student t-test or Fisher exact test. The association between underweight at Age 5 and physical characteristics at birth were determined by multiple logistic regression analysis, with odds ratios (ORs) and confidence intervals (CIs). The characteristics of LBW children included sex, birth weight, height, gestational age, the presence of small-for-gestational age (SGA), and multiple births in LBW children. Data analysis was performed using Excel Statistics, version 2010 (SSRI Co., Ltd., Tokyo, Japan). P values less than 0.05 were considered significant.
Physical characteristics at birth, including birth weight and height, gestational age, and the prevalence of SGA and multiple births, are shown in
The prevalence of underweight was significantly higher in LBW children than in NBW children in both sexes, except for boys at age 1.5 (
Total (n = 177) | Boys (n = 93) | Girls (n = 84) | P-value | |
---|---|---|---|---|
Birth weight (kg ± SD) | 1.64 ± 0.47 | 1.65 ± 0.45 | 1.63 ± 0.50 | 0.72b |
≥1.5 kg, <2.5 kg (%) | 112 (63.3) | 60 (64.5) | 52 (61.9) | 0.90c |
≥1.0 kg, <1.5 kg (%) | 46 (26.0) | 24 (25.8) | 22 (26.2) | |
<1.0 kg (%) | 19 (10.7) | 9 (9.7) | 10 (11.9) | |
Birth height (cm ± SD) | 40.3 ± 4.0 | 40.3 ± 3.8 | 40.3 ± 4.3 | 0.93b |
Gestational age (wk ± SD) | 32.7 ± 3.6 | 32.3 ± 3.3 | 33.2 ± 3.8 | 0.09b |
SGAa (%) | 42 (23.7) | 16 (17.2) | 26 (31.0) | <0.05c |
Muptiplebirths (%) | 34 (19.2) | 18 (19.4) | 16 (19.0) | 0.56c |
aSGA: Small for gestational age, defined as a sex-specific birth height and weight below the 10th percentile gestational age of the Japanese standard; bThe difference between genders was examined by the Student’s t-test; cThe difference between genders was examined by the Fisher’s exact test.
Boys | P-value a | Girls | P-valuea | |||
---|---|---|---|---|---|---|
LBW (n = 93) | NBW (n = 1267) | LBW (n = 84) | NBW (n = 1218) | |||
Height Z-score | ||||||
Birth | −4.12 ± 1.8 | 0.17 ± 0.94 | <0.001 | −3.91 ± 2.07 | 0.14 ± 0.98 | <0.001 |
1.5 y | −0.84 ± 2.1 | 0.17 ± 1.61 | <0.001 | −0.81 ± 1.70 | 0.17 ± 1.66 | <0.001 |
3.5 y | −0.67 ± 1.3 | −0.05 ± 1.29 | <0.001 | −0.50 ± 1.26 | 0.04 ± 1.21 | <0.001 |
5 y | −0.35 ± 1.3 | 0.23 ± 1.13 | <0.001 | −0.34 ± 1.43 | 0.25 ± 1.18 | <0.001 |
Increment of height Z-score | ||||||
Birth - 1.5 y | 3.28 ± 2.71 | 0.00 ± 1.70 | <0.001 | 3.10 ± 2.24 | 0.03 ± 1.79 | <0.001 |
1.5 y - 3.5 y | 0.17 ± 2.12 | −0.22 ± 1.18 | <0.05 | 0.31 ± 1.37 | −0.14 ± 1.28 | <0.01 |
3.5 y - 5 y | 0.32 ± 0.92 | 0.28 ± 1.11 | 0.34 | 0.16 ± 0.80 | 0.21 ± 1.02 | 0.26 |
Weight Z-score | ||||||
Birth | −3.37 ± 1.12 | 0.31 ± 0.80 | <0.001 | −3.44 ± 1.28 | 0.11 ± 0.76 | <0.001 |
1.5 y | −0.42 ± 0.97 | 0.18 ± 1.06 | <0.001 | −0.67 ± 1.37 | 0.32 ± 1.23 | <0.001 |
3.5 y | −0.51 ± 0.99 | −0.03 ± 0.95 | <0.001 | −0.53 ± 1.16 | 0.16 ± 0.99 | <0.001 |
5 y | −0.31 ± 1.00 | 0.11 ± 1.00 | <0.001 | −0.54 ± 0.99 | 0.14 ± 0.94 | <0.001 |
Increment of weight Z-score | ||||||
Birth - 1.5 y | 2.95 ± 1.33 | −0.12 ± 1.15 | <0.001 | 2.77 ± 1.50 | 0.20 ± 1.27 | <0.001 |
1.5 y - 3.5 y | −0.09 ± 0.67 | −0.21 ± 0.68 | 0.06 | 0.14 ± 0.80 | −0.16 ± 0.83 | <0.001 |
3.5 y - 5 y | 0.19 ± 0.55 | 0.14 ± 0.65 | 0.17 | −0.01 ± 0.60 | −0.02 ± 0.60 | 0.45 |
BMI % tile | ||||||
Birth | 6.9 ± 13.6 | 53.6 ± 26.8 | <0.001 | 6.6 ± 14.5 | 55.4 ± 26.7 | <0.001 |
1.5 y | 50.9 ± 30.4 | 51.8 ± 27.6 | 0.38 | 43.6 ± 31.5 | 55.5 ± 28.1 | <0.001 |
3.5 y | 49.5 ± 31.9 | 54.3 ± 26.4 | 0.08 | 38.5 ± 29.2 | 54.7 ± 26.6 | <0.001 |
5 y | 45.8 ± 30.5 | 49.6 ± 26.7 | 0.12 | 34.2 ± 27.4 | 50.5 ± 25.7 | <0.001 |
Data represents means ± SD. LBW: Low Birth Weight; NBW: Normal Birth Weight. aDifferences in the physical characteristics between LBW and NBW children were examined by the Student’s t-test.
We classified all LBW children into one of the three groups (underweight, normal weight, and obese) based on their BMI percentile at 5 years of age and compared the physical characteristics at birth between them. As shown in
Total | P-valuea | Boys | P-valuea | Girls | P-valuea | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
LBW (n = 177) | NBW (n = 2485) | LBW (n = 93) | NBW (n = 1267) | LBW (n = 84) | NBW (n = 1218) | |||||||
Prevalence of underweight | ||||||||||||
Birth | 127 (71.8) | 35 (1.4) | <0.001 | 65 (69.9) | 21 (1.7) | <0.001 | 62 (73.8) | 14 (1.1) | <0.001 | |||
1.5 y | 18 (10.2) | 74 (3.0) | <0.001 | 5 (5.4) | 40 (3.2) | 0.19 | 13 (15.5) | 34 (2.8) | <0.001 | |||
3.5 y | 21 (11.9) | 61 (2.5) | <0.001 | 10 (10.8) | 32 (2.5) | <0.001 | 11 (13.1) | 29 (2.4) | <0.001 | |||
5 y | 23 (13.0) | 89 (3.6) | <0.001 | 10 (10.8) | 47 (3.7) | <0.01 | 13 (15.5) | 42 (3.4) | <0.001 | |||
Prevalence of obesity | ||||||||||||
Birth | 2 (1.1) | 270 (10.9) | <0.001 | 1 (1.1) | 126 (9.9) | <0.001 | 1 (1.2) | 144 (11.8) | <0.001 | |||
1.5 y | 22 (12.4) | 284 (11.4) | 0.34 | 14 (15.1) | 121 (9.6) | 0.07 | 8 (9.5) | 163 (13.4) | 0.25 | |||
3.5 y | 15 (8.5) | 211 (8.5) | 0.55 | 12 (12.9) | 109 (8.6) | 0.11 | 3 (3.6) | 102 (8.4) | 0.08 | |||
5 y | 10 (5.6) | 145 (5.8) | 0.54 | 8 (8.6) | 76 (6.0) | 0.21 | 2 (2.4) | 69 (5.7) | 0.15 | |||
LBW: Low Birth Weight; NBW: Normal Birth Weight. aThe prevalence of underweight and obesity between LBW and NBW children was compared by the Fisher’s exact test.
Body status at 5 years | |||
---|---|---|---|
Thin (n = 23) | Normal weight (n = 144) | Obese (n = 10) | |
Sex (boys %) | 10 (43.5) | 75 (52.1) | 8 (80.0) |
Birth weight (kg ± SD) | 1.52 ± 0.49 | 1.66 ± 0.47 | 1.67 ± 0.55 |
≥1.5 kg, <2.5 kg (%) | 10 (43.5)b | 96 (66.7) | 7 (70.0) |
≥1.0 kg, <1.5 kg (%) | 11 (47.8)b | 31 (21.5) | 2 (20.0) |
<1.0 kg (%) | 2 (8.7)b | 17 (11.8) | 1 (10.0) |
Birth height (cm ± SD) | 39.6 ± 4.3 | 40.4 ± 4.0 | 39.6 ± 5.0 |
Gestational age (wk ± SD) | 34.0 ± 3.6 | 32.6 ± 3.5 | 31.7 ± 3.8 |
SGAa (%) | 16 (69.6)c | 26 (18.1) | 0 (0.0) |
aSGA: Small for gestational age, defined as a sex-specific birth height and weight below the 10th percentile for gestational age of the Japanese standard; bSignificantly different from normal-weight children, P < 0.05 (Fisher’s exact test); cSignificantly different from normal-weight children, P < 0.001 (Fisher’s exact test).
Monitoring growth and neurological development are key issues in the follow-up of LBW children [
In the present study, we demonstrated that LBW children experienced accelerated growth from birth to age 3.5 years, but that they still had significantly smaller height and weight z-scores than the NBW controls, regard- less of sex, at Age 5. These results were consistent with those of previous studies, in which preterm or VLBW children showed steady increases in height and weight standard deviation scores from birth to Age 6, but that they remained smaller and lighter than their term-born or NBW peers [
Dependent variables | Independent variable: Underweight at 5 years | |||
---|---|---|---|---|
Coefficient (95% CI) | Standardized coefficient | OR (95% CI) | P-value | |
Sexa | 0.02 (−0.98, 1.03) | 0.01 | 1.02 (0.38, 2.79) | 0.95 |
Birth weight (kg) | 0.31 (−1.24, 1.87) | 0.15 | 1.37 (0.29, 6.47) | 0.67 |
Birth height (cm) | −0.12 (−0.33, 0.10) | −0.46 | 0.89 (0.72, 1.11) | 0.32 |
Gestational age (wk) | 0.05 (−0.22, 0.31) | 0.16 | 1.05 (0.80, 1.36) | 0.79 |
SGAb | 2.10 (0.70, 3.49) | 0.91 | 8.14 (2.01, 32.93) | <0.001 |
Muptiple births | −0.83 (−2.43, 0.78) | −0.33 | 0.44 (0.09, 2.17) | 0.35 |
(R² = 0.53) |
Ten obese children were excluded from this analysis. aFor the analysis, 1: Boys, 0: Girls, 1: AGA, 0: AGA, 1: Multiple births, 0: Single birth, were allocated. bSGA: Small for gestational age, defined as a sex-specific birth height and weight below the 10th percentile for gestational age of the Japanese standard.
adults born preterm or LBW have also been shown to be shorter and lighter than their peers [
Since catch-up growth for height and weight is not necessarily proportionate [
When comparing LBW and NBW children, we found a significant difference only in BMI percentiles for girls, except for at birth. A possible reason for this difference between the sexes was that the prevalence of SGA was significantly higher in LBW girls compared with that in LBW boys. The prevalence of underweight was significantly higher at Age 5 in both sexes, and the multiple regression analysis indicated that SGA at birth was only associated with underweight in 5-year-old children. Indeed, a review of childhood undernutrition risk based on SGA and preterm birth found that SGA, irrespective of gestational age, was risk factor for underweight at 12 - 60 months compared with AGA or term births [
A number of studies have examined the relationship between birth weight and overweight or obesity [
There are several limitations in the present study. First, the retrospective design resulted in a substantial number of children without present addresses at the time of investigation and a questionnaire return rate of approximately 37%. In addition, the investigation was carried out at single hospital in the Nara Prefecture. These facts undoubtedly led to a degree of selection bias that must be considered in any interpretation. Second, we followed the growth of LBW children from birth to Age 5 only, making a longer follow-up study to later childhood or adulthood necessary. Third, the study collected only height and weight as anthropometric measures and used BMI as the sole indicator for assessing adiposity in children. Other anthropometric indicators, such as waist circumference [
A major strength of this study was that it examined the growth of LBW children from birth to Age 5 longitudinally. Moreover, the data for LBW children were compared with a large sample of NBW children, with particular attention given to the prevalence of both underweight and obesity. The accuracy of the data obtained from mother-health child records maintained by the mother is also considered as strength. In Japan, a regular health check is carried out by experts at birth and at Ages 1.5 and 3.5 years, and the results are recorded in these notebooks.
The prevalence of underweight was higher in LBW children than in NBW controls, but the rates of obesity were comparable. Thus, our data support underweight being a more serious problem than obesity in LBW children at Age 5. The facts that height and weight z-scores were significantly lower at each time point, and that SGA was the only risk factor for underweight at Age 5, were important findings. These suggest that careful observation of growth and intervention from early infancy may be necessary to prevent the development of underweight.
The authors declare that they have no competing interests.
The authors would like to thank the participants in the study. The authors would also like to thank Enago (www.enago.jp) for the English language reviews.
RenaKato,MasaruKubota,HiromiSaito,YukihiroTakahashi, (2015) Underweight and Obesity in Low Birth Weight Children in Early Infancy in Japan. Food and Nutrition Sciences,06,339-347. doi: 10.4236/fns.2015.63034