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Community paediatrics
Original research
Growth trajectory of full-term small-for-gestational-age infants: a 3-year longitudinal study in China
  1. Jianwei Zhang1,
  2. Xinyu He2,
  3. Lujia Ma1,
  4. Ziqiao Li2,
  5. Wenxia Shen1,
  6. Mengdi Hua2,
  7. Lidan Sun2,
  8. Guannan Bai2
  1. 1Shaoxing Maternity and Child Health Care Hospital, Shaoxing, Zhejiang, China
  2. 2Department of Child Health Care, Children’s Hospital, Zhejiang University School of Medicine, National Clinical Research Center for Child Health, Hangzhou, Zhejiang, China
  1. Correspondence to Guannan Bai; guannanbai{at}zju.edu.cn

Abstract

Objective Small-for-gestational-age (SGA) infants are at risk of impaired growth and developmental outcomes, even for those who were born at full term. The growth trajectory of full-term SGA infants remains unknown. Therefore, this study aimed to evaluate the growth trajectory of full-term SGA infants from birth to 3 years old in East China.

Methods Full-term SGA infants were followed up from birth to 3 years old. The weight and length were measured at 3, 6, 12, 18, 24, 30 and 36 months. Rate of catch-up growth and rates of growth deviations including short stature, emaciation, underweight, overweight and obesity, were calculated at different time points. Latent class analysis was applied to describe growth trajectories from birth to 36 months.

Results A total of 816 full-term SGA infants were enrolled in this study and 303 had complete follow-up data at 3, 6, 12, 18, 24, 30 and 36 months. At 24 months, the rate of catch-up growth was 42.4% in girls and 48.6% in boys; while at 36 months, this rate was 43.3% in girls and 52.1% in boys. The latent class analysis identified two trajectories of weight and length in boys and girls. Girls showed different growth trajectories of weight since 12 months compared with boys.

Conclusions Our study reported a relatively low rate of catch-up growth in full-term SGA infants and has identified different growth trajectories of length and weight in boys and girls. We call for attention from health professionals on the growth trajectory of full-term SGA infants to eventually promote their health potentials.

  • Growth
  • Health services research
  • Infant

Data availability statement

Data are available upon reasonable request.

http://creativecommons.org/licenses/by-nc/4.0/

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

https://doi.org/10.1136/bmjpo-2023-002278

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    WHAT IS ALREADY KNOWN ON THIS TOPIC

    • Full-term small-for-gestational-age (SGA) infants are still at risk for growth retardation and obesity. Catch-up growth (CUG) is an important biological process in full-term SGA infants. Despite the health benefits of CUG, CUG may be related to a higher risk of overweight or obesity, cardiovascular disease and metabolic disorders in later life.

    WHAT THIS STUDY ADDS

    • The rate of CUG in the whole sample was low. There were different growth trajectories of length and weight in boys and girls.

    HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY

    • Our study suggested that the weight of a subgroup of girls may increase rapidly and the length of a subgroup of girls was always lower than APA reference of WHO standard, while in boys such pattern was not observed. Health professionals should pay more attention to the weight and length growth in girls. Findings in this study could be interpreted into health management strategies for the full-term SGA infants by developing age-specific and gender-specific interventions.

    Introduction

    Fetal growth restriction is an important indicator of neonatal health for both preterm and full-term infants and adversely influences the short-term and long-term growth and developmental outcomes. Usually, it is assessed by comparing the birth weight with the expected weight for the same gestational age from a reference population with a normal fetal growth. Small for gestational age (SGA) is a widely used term to describe an infant with birth weight below the 10th percentile for gestational age.1 The global prevalence of SGA is around 16% and the range varies from 7% in developed countries to 27% in the low-income and middle-income countries where 91.7% were born full term.2 3 In China, the prevalence is 6.5%.4 There are multiple associated factors of SGA, but the aetiology remains unclear. SGA is mainly related to quality of perinatal healthcare, lifestyle (e.g., malnutrition, smoking, drinking and drug abuse), placenta, pregnancy complications and environmental factors.5

    SGA can predict the growth risk of newborns and is associated with various developmental issues, such as short stature, obesity, metabolic complications and cognitive developmental impairments.4 6–9 According to the Child Health Epidemiology Reference Group, SGA was associated with increased risk of neonatal and postneonatal mortalities compared with infants born appropriate for gestational age (AGA).10 Up to 90% of the SGA infants experience an accelerated growth during the first year of life that results in a height above 2 SDs. Most of the catch-up growth (CUG) occurs during the first year and is nearly completed by the age of 2 years.11 This CUG may have long-term benefits on achieving a normal height.12 13 Birth cohort studies have shown that reduced birth weight is usually followed by rapid infant weight gain.14 15 Abali et al found that about one-third of the SGA infants were overweight or obese while only one-fifth of those born AGA were overweight or obese at the second year.16 Even born full term, the SGA neonates are still at risk of growth retardation, obesity and neurocognitive disorders during childhood as well as metabolic syndromes and psychosocial dysfunction during adulthood.17 Therefore, it is necessary to investigate the growth characteristics such as the CUG, growth deviations and growth trajectories in children who were born full-term SGA. Few such data exist in terms of this issue.

    Hence, we conducted a longitudinal study by following up 816 full-term SGA infants from birth to the age of 36 months. The primary aim was to assess the rate of CUG, rates of growth deviations as well as the overall growth trajectories of full-term SGA infants, and the secondary aim was to identify the potential determinants of growth trajectories of these infants.

    Methods

    Study design and participants

    The present study is an observational and retrospective cohort study. We included the full-term SGA infants who were born from January 2010 to February 2019 in Shaoxing Maternal and Child Health Care Hospital (Shaoxing, Zhejiang Province, China) and followed them up until 36 months. The inclusion criteria were as follows: (1) being born as full term, that is, gestational age ≥37 and <42 weeks; and (2) SGA infants, that is, the birth weight was below the 10th percentile or a neonate with a birth weight of <2 SDs below the mean for gender-specified birth weight standards.18 Infants with congenital heart defect, genetic metabolism and chromosomal disorders were excluded. Gestational age at birth is determined by ultrasound measurements during the mother’s last menstrual period or early pregnancy. According to the National Basic Public Health Service Regulation (2011), infants, especially those with high-risk birth outcomes such as SGA, should be followed up closely at 3, 6, 12, 18, 24, 30 and 36 months.

    Since data used in this study were retrieved from electronic records in the hospital, and no additional physical harm was added to the participants due to this study, informed consent was waived by the Medical Ethics Committee. The present study was conducted according to the Declaration of Helsinki.

    Data collection

    Weight and length were measured at birth and at 3, 6, 12, 18, 24, 30 and 36 months after birth by well-trained nurses. Weight was measured by an electronic scale (Seca 376; Seca Measuring Systems, Hong Kong, China). Length was measured in the supine position of the measuring bed (Seca 416; Seca Measuring Systems). The accuracy of weight and length was close to 0.1 kg and 0.1 cm, respectively. Body mass index (BMI) is calculated by dividing the weight in kilograms by the square of the length in metres. In addition, we extracted clinical information including maternal weight, height, educational level, pregnancy complications, distress and health conditions during pregnancy from the electronic health system of the study hospital.

    Growth parameters

    The WHO Growth and Development Standards for children in 2006 were selected as the growth and development reference.19 Height-for-age z-score(HAZ) was calculated by dividing the difference between the measured value of the subjects and the average measured value of the control group by the SD of the reference group. In the current study, catch-up growth (CUG) for SGA infants was defined if the growth velocity is greater than the median for chronological age and gender, that is, the growth velocity >0 SD.18 The growth velocity was calculated by change in z-score (Δ z-score) between certain follow-up intervals.

    Growth deviation refers to short stature, emaciation, underweight, overweight and obesity in the present study. Short stature was defined if the length was below −2 SDs of length for their age and gender. Emaciation was defined as low weight for length and below −2 SDs. BMI z-score and percentile were calculated using sex-specific values according to the 2006 WHO Growth and Development Standards by using WHO Anthro 2009 software.20 Cut-offs were defined as follows: underweight as BMI z-score <−1 SD; normal weight as −1 SD≤BMI z-score≤1 SD; overweight as BMI z-score >1 SD; and obesity as BMI z-score >2 SDs.21

    Statistical analyses

    First, we checked the normality of contentious variables and found our data were not normally distributed, so we calculated medians and interquartile ranges (IQRs), that is, 25th–75th percentiles. Regarding categorical variables, we counted numbers and calculated percentages. Second, we applied two independent samples t-tests for normally distributed data, while the Mann–Whitney U test for non-normally distributed data; and we applied the χ2 tests for categorical variables to compare the differences between groups. Then, we used the WHO growth curve as the reference and compared the length, weight and BMI in our study with the references. Lastly, we conducted the latent class analysis to distinguish certain growth trajectories (or the so-called latent classes) regarding weight and length in both boys and girls. The growth trajectory refers to a group of children who share a common underlying pattern of weight and length growth over time. We included those with complete data at seven times of follow-up (n=303) for the latent class modelling. In addition, we applied the latent class analysis to all the available cases and used multiple imputation regarding the missing values, as the percentages of missing at each time point were no more than 30%. The optimal number of classes was evaluated by model fit statistics, that is, the Akaike information criterion (AIC), Bayesian information criterion (BIC) and entropy levels. χ2 tests and one-way analysis of variance were used to assess the differences between different latent classes (or trajectories).

    In addition, we conducted the non-response analysis by comparing the attributes during pregnancy and at birth between children who had complete data at seven times of follow-up and those who missed any one time of follow-up. We then conducted analysis by comparing the attributes between these groups regarding different trajectories of length and weight in both boys and girls.

    All statistical analyses were performed using SPSS V.16.0 (IBM) and R V.4.1.0 (package ‘lcmm’). P value <0.05 indicates the statistical significance.

    Results

    General and clinical characteristics of full-term SGA infants

    Table 1 presents the general and clinical characteristics of 816 full-term SGA infants who were enrolled at birth. The median gestational age at birth was 37.6 weeks; 488 (59.8%) were girls. The median of birth weight was 2360 g. The median of maternal weight and height was 64.50 kg and 158.0 cm, respectively. 501 (61.4%) mothers delivered by caesarean section and 10.4% had twins. Regarding pregnancy complications, 5.6% of mothers had hypertension or hypertension-related diseases; 3.6% had diabetes or gestational diabetes; 1.8% had anaemia; and 1.2% had thyroid dysfunction. During delivery, 2.9% of mothers had premature rupture of membranes and 2.6% had oligohydramnios. 2.3% of the newborns experienced fetal distress and 1.8% were delivered with a breech presentation. There is no gender difference between the above characteristics.

    View this table:
    Table 1

    General characteristics of the study population at baseline (n=816)*

    Weight, length and BMI of children from birth to 3 years old

    Figure 1 shows the medians of z-scores of weight, length and BMI of full-term SGA boys and girls from birth to 36 months and the specific values are presented in online supplemental table S1. In boys, the median of z-score of weight increased since 3 months and reached the highest level at 12 months (ie, 0.22), then decreased slowly, indicating that the SGA children catch up fastest at 12 months. Similar to weight, the highest z-score of length was observed at 12 months (ie, 0.37), and since then it decreased until the lowest at 24 months (ie, −0.13). The pattern of BMI was similar to that of the weight. In girls, all the medians of z-scores were lower than 0. The highest medians of z-scores of weight, length and BMI were observed at 12 months. Since then, the median of z-score of weight decreased to the lowest at 36 months (ie, −0.5).

    Supplemental material

    Figure 1
    Figure 1

    Medians of z-scores of weight, length and body mass index (BMI) of full-term small-for-gestational-age (SGA) boys and girls from birth to the age of 36 months.

    Figure 2 shows the medians of weight, length and BMI of full-term SGA boys and girls at each follow-up time point using the age-specific and gender-specific values of appropriate-for-gestational-age (AGA) children as references according to the WHO standards. Regarding weight, medians of SGA boys were below the curve of medians of AGA children according to the WHO standards at all time points; while for girls medians were closely similar to medians of AGA children at 3, 6, 9 and 12 months, and from 18 months, medians of SGA children were lower than medians of AGA children until 36 months. Regarding the length, the trajectory curve of boys was close to the curve of ‘AGA-1 SD’ from 3 months to 18 months, and since then it raised up to reach the curve of median of AGA boys. For girls, the median curve was very similar to the median curve of AGA girls. Regarding BMI, the median curves were between the curve of median and the curve of ‘AGA-1 SD’ at all time points in both boys and girls.

    Figure 2
    Figure 2

    Medians of weight, length and body mass index (BMI) of full-term small-for-gestational-age (SGA) boys and girls from birth to the age of 36 months with reference to WHO standards. AGA, appropriate for gestational age.

    Growth deviation

    Table 2 shows rates of growth deviation at each follow-up time point of full-term SGA children. Only 52.1% of boys and 43.3% of girls showed complete CUG at 36 months. The highest rates of underweight, short stature and emaciation were observed at 3 months in both boys and girls. Regarding overweight, the highest rate in boys was at 3 months (ie, 8.14%), and in girls at 24 months (ie, 6.70%). Regarding obesity, the highest rate in boys was at 12 months (ie, 3.15%), and at 36 months in girls (ie, 2.43%).

    View this table:
    Table 2

    Rates of growth deviation of full-term SGA infants at 3, 6, 12, 18, 24, 30 and 36 months

    Growth trajectories

    Latent class analysis models have identified the growth trajectories of weight and length in boys and girls in both imputed data and complete data. Two latent classes were identified as the optimal number of latent classes. Online supplemental tables S2–S9 present the values of model fits (such as AIC and BIC) as well as entropy levels using both imputed data and complete data. Online supplemental table S10 presents the values of medians and IQRs of length and weight in two classes in both boys and girls. Figure 3 illustrates the weight growth trajectories in our study with reference to WHO standards. Regarding weight in 118 boys with complete follow-up data, class 2 contained 28.9% boys (n=34), which grew relevantly faster than class 1 (n=84). Differences in weight between class 1 and class 2 in boys were only statistically significant at 30 months (difference=0.5 kg, p=0.034) and 36 months (difference=1.5 kg, p<0.001). In girls, class 1 contained 153 individuals and class 2 contained 32 individuals. Differences between class 1 and class 2 were statistically significant at 18, 24, 30 and 36 months (p<0.05). More specifically, the differences were 0.9 kg at 18 months (p=0.008), 1.5 kg in 24 months (p<0.001), 1.7 kg in 30 months (p<0.001) and 2.7 kg in 36 months (p<0.001). Additionally, online supplemental figure S1 shows the trajectories of gender-specific weight in both imputed data and complete data with references to WHO standards. The two trajectiories of weight in boys are more or less the same when using imputed data and complete data. But in girls, we observed some difference. More specifically, the class 1 identified in the imputed data is close to the the growth of infants born apropriate-for-gestational-age (AGA), and the weight is lower than that in class 1 identified in the complete data since 18 months after birth until 36 months, while class 2 identified in the imputed data is always below the growth trajectory (ie, class 2 identified in the complete data) from birth to the age of 36 months.

    Supplemental material

    Figure 3
    Figure 3

    Growth trajectories of gender-specific weight of full-term small-for-gestational-age (SGA) infants from birth to 36 months with references to WHO standards. AGA, appropriate for gestational age.

    Figure 4 illustrates the growth trajectories of length with reference to WHO standards. Two latent classes were identified for boys with 69 individuals in class 1 and 49 in class 2. Two latent classes were identified for girls with 139 individuals in class 1 and 46 in class 2. Differences in length between two latent classes were significant in boys at 6 months (difference=1 cm, p=0.02) and 24 months (difference=1.5 cm, p=0.02). In girls, the average body length in class 2 at each time point was longer than that in class 1. Differences in length between two latent classes were significant in girls at 3 months (difference=1.0 cm, p=0.048), 6 months (difference=2.6 cm, p<0.001), 18 months (difference=2.4 cm, p<0.001), 24 months (difference=2.8 cm, p<0.001) and 30 months (difference=2.8 cm, p<0.001). Additionally, online supplemental figure S2 shows the trajectories of gender-specific length in both imputed data and complete data with reference to WHO standards. The growth trajectories of length identified in the imputed data are similar to those identified in the complete data in both boys and girls.

    Supplemental material

    Figure 4
    Figure 4

    Growth trajectories of gender-specific length of full-term small-for-gestational-age (SGA) infants from birth to 36 months with reference to WHO standards. AGA, appropriate for gestational age.

    Risk factors were compared between latent classes of weight and length in both boys and girls. In girls’ length model, only mother’s weight and birth weight were statistically significantly different between class 1 and class 2 (p values<0.05).

    In addition, online supplemental table S11 shows the results of non-response analysis. Children included in the analysis were more often twins (p<0.05) and more often had complications at birth, such as premature rupture of membranes, oligohydramnios, fetal distress and breech presentation, compared with those excluded from the analysis (p values<0.05). Mothers of children included in the analysis were higher, heavier during pregnancy, with higher education and more often had complications during pregnancy, such as hypertension or hypertension-related diseases and anaemia, compared with those whose children were excluded from the analysis (p values<0.05). Online supplemental tables S12 and S13 show attributes between groups regarding different trajectories of length and weight in both boys and girls. We found that attributes in boys and girls across different trajectories are almost the same. As shown in online supplemental table S12, we did not find statistically significantly different attributes across different groups of length and weight trajectories in boys. As shown in online supplemental table S13, regarding length trajectories, the birth weight of girls in class 1 was heavier than those in class 2 (p<0.05), and the weight of their mothers during pregnancy was also heavier than those in class 2 (p<0.05). Regarding weight trajectories, all the differences in attributes were not statistically significant except for the mode of delivery (p=0.010).

    Discussion

    Due to intrauterine growth retardation, full-term SGA infants have increased risk of ectopic growth retardation and neurological abnormalities.22 In this study, we evaluated growth parameters longitudinally and distinguished different patterns of growth trajectories in length and weight of full-term SGA infants using latent class analysis. We found that full-term SGA infants showed rapid growth after birth, and particularly by 6 months of age, but only 52.1% of girls and 43.3% of boys completed catch-up in length. The rate of CUG in the whole sample was lower than the previous findings (ie, 85%).23

    We found almost equivalent attributes across groups of different trajectories. The potential explanation might be that some other impact factors for growth trajectories were not measured in the present study, even though we had detailed medical records of attributes of maternal health during pregnancy and neonatal health at birth. Previous studies have shown that SGA infants can show different growth patterns after birth. The growth hormone (GH)-insulin-like growth factor-1 system may play an important role.24 25 The height of parents affects the height of offspring,26 and timely GH treatment can significantly improve the height of SGA.27 The present study only had information on maternal height, and father’s height was not recorded. Thus, we were not able to evaluate whether there was difference in father’s height across different groups of growth trajectories. SGA functional retardation may be associated with insulin sensitivity, which can continue to lead to different growth patterns after birth.28 Animal experiments have shown that maternal blood lipid levels during pregnancy can affect the growth pattern of offspring.29 Kaneko et al also found that high total cholesterol levels in the second trimester of pregnancy can lead to deviations in infant growth.30 Our study did not have such information as mentioned above.

    We found different growth patterns in terms of length and weight in both boys and girls. The results of the latent class analysis of weight suggested that girls showed different trajectories compared with boys. More specifically, the weight of one group (ie, class 1 in our study) of girls stayed below the median (ie, AGA), and the weight of another group (ie, class 2 in our study) increased rapidly after 12 months and was higher than AGA, almost reaching AGA+1 SD at the age of 36 months. The disparity of weight between class 1 and class 2 in girls became much larger from 12 months until 36 months. In other words, our study has identified a subgroup of girls who had rapid weight gain from 12 months to 36 months. Rapid growth in weight during infancy in full-term SGA may be associated with an increased risk of overweight/obesity. A recent study in Denmark suggested that rapid weight gain among infants between 0 and 8–10 months dramatically increased the risk of overweight and obesity at 2 years.31 Ong and Dunger found that full-term SGA who developed CUG between 0 and 2 years of age had more body fat distribution at 5 years of age than other children.32

    There is growing evidence that children who grow up quickly during childhood are more likely to be obese and have metabolic disorders such as insulin resistance and non-insulin-dependent diabetes, hypertension and cardiovascular disease during adulthood.33 Li et al34 found that the extremely rapid weight gain pattern of term SGA infants from birth to 2 years was significantly related to the increased risk of overweight/obesity at 2–5 years in later life. The risk was approximately two times higher than that of full-term non-SGA infants.35 Hack et al found that 21% of very-low-birthweight infants were overweight, and 15% were obese at age of 20 years,36 and that full-term SGA infants were twice as likely to be obese than AGA children. Although there were some disparities in risks due to the different study designs and populations, it was clear that rapid weight gain in early life may significantly increase the risk for overweight/obesity in later life.

    On the other hand, research suggested that the risk for short stature in those born SGA was five to seven times higher than that in children born AGA. It was estimated that 8–14% of children born SGA did not experience sufficient CUG by the age of 3 years and were therefore at risk of short stature during adulthood.9 37 The possibility of catch-up in height by 3 years of age is likely to be low when full-term SGA children have not caught up by 4 months of age.11 We also found in latent class analysis that the body length of a subgroup of SGA girls was short, and was always below the AGA reference of WHO standard, so it was necessary to be alert to the continuous backwardness of growth.

    There are also many factors that affect the growth trajectory of SGA infants, including socioeconomic factors, genetic factors, maternal prenatal factors, maternal pregnancy complications, etc.35 38 39 We further compared characteristics during pregnancy and at birth across latent classes of length and weight, and found that mothers of girls in latent class 1 of length had heavier weight during pregnancy than mothers of girls in latent class 2; the measurement of length at each time point in latent class 1 was lower than that of latent class 2. We suggested further studies to verify the negative correlation between maternal weight during pregnancy and the length of children.

    SGA infants require good monitoring and management, especially in those with rapid catch-up weight growth, tend to have a higher risk of obesity and metabolic syndromes later in life and therefore require early identification and early intervention. The Latin American expert consensus recommends following up by measuring length and weight every 3 months within 1 year of age and every 6 months between 1 and 2 years of age.40 In the area where this study was conducted, SGA infants were managed as high-risk children that should be closely monitored. Health professionals in the tertiary network of monitoring, that is, city-county-community healthcare centres, routinely follow up these infants at birth and at 3, 6, 9, 12, 18, 24, 30 and 36 months. We suggested that health professionals, including clinicians and nurses, make accurate measurement of length and weight for full-term SGA infants at each follow-up and draw growth curves of both length and weight. By doing so, both health professionals and parents would be alerted immediately when suboptimal growth trajectory occurs, for instance, the rapid weight gain. Health professionals should pay more attention to the weight and length growth in girls. Findings in this study could be interpreted into health management for the full-term SGA infants by developing age-specific and gender-specific interventions.

    Strengths and limitations

    The present study is one of the few that applied the latent class analysis to distinguish the growth trajectories of length and weight among full-term SGA infants. In addition, due to the longitudinal study design, causation may be derived compared with the previous studies that were mostly cross-sectional. However, there were several limitations that required attention. First, there were many infant dropouts from the follow-ups, which may bring selection bias. We conducted non-response analysis and found that infants who had complete data on follow-ups were more often twins, and their mothers had relatively high education and had more diseases at birth. In other words, children at relatively high risk of health were more likely to be followed up. Therefore, our results should be interpreted with caution. Second, because the data in the present study were extracted from the medical records, some information may not be collected, such as nutrition during pregnancy, maternal distress level, feeding (ie, breast feeding and formula), etc. Third, we used the complete data of length and weight at seven time points of follow-ups as the main dataset for analysis, and additionnally we applied the multiple imputation or full-information maximum likelihood approach to deal with the missing data (see supplementary files). Children with complete data had different attributes compared with those who were excluded from the analysis. More specifically, children with complete follow-up data were more often twins and had more health conditions at birth, while their mothers had more health conditions during pregnancy. This may limit the generalisation of our findings. Lastly, the relatively small sample size in each latent class is also a limitation and we ask for caution when interpreting our data. We highly recommended other researchers to replicate the analysis in the large-scale birth cohort studies to confirm or to reject our conclusions.

    Conclusion

    Our study reported a relatively lower rate of catch-up gowth in full-term SGA infants than previous studies and has identified different growth trajectories of length and weight in boys and girls. We call for attention from health professionals on the growth trajectory of full-term SGA infants to eventually promote their health potentials.

    Data availability statement

    Data are available upon reasonable request.

    Ethics statements

    Patient consent for publication

    Ethics approval

    The study was approved by the Ethics Committee of Shaoxing Maternal and Child Health Care Hospital (2021006).

    Acknowledgments

    We thank all members of the Bai Lab and Pediatric Evidence-based Medical and Clinical Research Laboratory in the National Clinical Research Center for Child Health, Children’s Hospital, Zhejiang University School of Medicine, for the interesting discussions and great contributions to the project. We are grateful for the valuable support from Miss Meiying Gao (MSc) who handled the additional statistical analyses during the revision.

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    Supplementary materials

    Footnotes

    • Contributors JZand GB conceived and designed the study. JZ and GB wrote the manuscript.

      GB was responsible for the overall content as the guarantor. LM and WS provided patient care and were responsible for communication with the parents. XH, ZL, MH and LS performed the data analysis. All of the authors have reviewed and approved the final version of the manuscript.

    • Funding This work was supported by the Health Commission of Zhejiang Province (2021KY1155) and the Health Commission of Shaoxing City (2022KY040).

    • Competing interests None declared.

    • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.