Objective: To determine the correlation between obesity related indicators and blood lipid levels among children and adolescents. Methods: A total of 5 812 participants were included. Height, weight, body composition, waist circumference, blood pressure were measured and fasting glucose and blood lipid levels were tested based on a cross sectional survey of children and adolescents 6-17 years in Beijing, 2022-2023. The body mass index (BMI), fat mass index (FMI), body roundness index (BRI) and waist to height ratio (WHtR) were calculated. Linear and Logistic regression were used to analyze the associations between the four obesity indicators (BMI, FMI, BRI, and WHtR) and blood lipids in children and adolescents. The area under the curve (AUC) of the receiver operating characteristic (ROC) was used to evaluate differences in the associations between different obesity indicators with dyslipidemia. Results: Linear regression showed that BMI, FMI, BRI, and WHtR were positively correlated with triglyceride (TG), low density lipoprotein cholesterol (LDL-C), and non high density lipoprotein cholesterol (non HDL-C) levels (boys: β 6-9 years =0.02-0.28, β 10-17 years =0.02-0.37; girls: β 6-9 years =0.02-0.28, β 10-17 years =0.03-0.25), and negatively correlated with the high density lipoprotein cholesterol (HDL-C) level in both genders across age subgroups (boys: β BMI = -0.03, β FMI = -0.04 , β BRI =-0.09, β WHtR =-0.17; girls: β BMI =-0.03, β FMI =-0.04, β BRI =-0.11, β WHtR =-0.20) (all P <0.01). The associations between total cholesterol (TC) and remnant cholesterol (RC) levels with obesity indicators differed significantly by gender and age. The TC level was positively associated with obesity indicators in boys of all ages ( β BMI =0.01, β FMI =0.03, β BRI = 0.08 , and β WHtR =0.16) but only with FMI, BRI, and WHtR in girls 6-9 years of age ( β FMI =0.02, β BRI =0.05, and β WHtR =0.08) (all P <0.05). The RC level had a negative correlation with BRI in boys 10-17 years of age ( β =-0.01) and a positive correlation with BMI in girls 6- 9 years of age ( β =0.00) (all P <0.05). Logistic regression indicated that elevated obesity indicators were significantly associated with higher risks of elevated TG, LDL-C, and non HDL-C levels and a decreased HDL-C level in all gender age stratas (all P <0.01). Only the BMI and FMI in girls 6-9 years of age were significantly related to a high RC ( OR =1.07, 1.07, both P <0.05). ROC analysis revealed that FMI, BRI, and WHtR were more predictive than BMI of elevated TG, LDL-C, and non HDL-C levels. The BMI was superior in predicting a decreased HDL-C level in boys, while no significant difference was detected among indicators in girls. Indeed, all obesity indicators had poor predictive performance for elevated TC, RC, and LDL-C levels in girls (all AUC<0.7). Conclusions Obesity indicators reflecting body fat content and fat distribution are shown to be closely associated with dyslipidemia in children and adolescents with obvious age and gender differences. The FMI, BRI, and WHtR have potential advantages in the early identification of dyslipidemia among children and adolescents compared to the BMI alone.

Objective:To understand the current status of pubertal sexual characteristics development of girls aged 6-18 years in Tongzhou District of Beijing and to compare the differences in sexual characteristics development among girls characterized as thin, normal, overweight, and obese.Methods:A cross-sectional survey was conducted among 2 844 girls aged 6-18 years in Tongzhou District of Beijing from September 2022 to July 2023. The developmental stages of breast and pubic hair were assessed on site, and menarche status was inquired. Weight and height were measured. The girls were subsequently characterized into thin, normal, overweight and obese groups. Basic information (including family and personal history) was obtained through questionnaires. Probit probability unit regression was applied to calculate the age of each Tanner stage of sexual characteristics development and the age of menarche. The χ 2 test was applied to compare the counting data between two or multiple groups. Results:A total of 2 844 girls were surveyed and 2 704 girls met the inclusion criteria, resulting in a valid response rate of 95.1%. Among these girls, 1 105 (40.9%) were aged 6-9 years, 1 053 (38.9%) were aged 10-13 years, and 546 (20.2%) were aged 14-18 years. The of height-for-age Z-score (HAZ), weight-for-age Z-score (WAZ), and body mass index-for-age Z-score (BAZ) were 0.46(-0.23,1.16), 0.69(-0.16,1.67), and 0.67(-0.27,1.73) respectively. The prevalences of thin, overweight, and obesity were respectively 1.7% (45/2 704), 17.3% (467/2 704), and 19.9% (538/2 704), respectively. There were 45 girls in the thin group, 1 654 girls in the normal weight group, 1 005 girls in the overweight and obesity group. The age of Tanner stage breast 2 (B2), Tanner stage pubic hair 2 (P2), and menarche was 9.0 (95% CI 8.9-9.1), 10.5 (95% CI 10.4-10.6), and 11.4 (95% CI 11.3-1.5) years, respectively. The current status of breast and pubic hair maturity in girls with pubertal development shows that 64.6% (1 211/1 874) of these girls had breast development preceding pubic hair development, 32.4% (607/1 874) had concurrent breast and pubic hair development, and 3.0% (56/1 874) had pubic hairs development preceding breast development. The interval age between B2 and B5 was 4.7 (95% CI 4.6-4.8) years, between P2 and P5 was 4.5 (95% CI 4.4-4.6) years, and between B2 and menarche was 2.4 (95% CI 2.3-2.5) years. The ages of sexual characteristics development in overweight and obese groups were earlier than that in normal and thin groups. The ages of B2 in thin, normal, overweight, and obese groups were 10.0 (95% CI 9.5-10.6), 9.3 (95% CI 9.2-9.4), and 8.6 (95% CI 8.4-8.7) years, respectively. The age of menarche in thin, normal, overweight, and obese groups were 13.1 (95% CI 12.4-13.7), 11.6 (95% CI 11.4-11.7), and 11.1 (95% CI 11.0-11.2) years, respectively. The interval ages between B2 and B5 and between P2 and P5 was 4.5 and 4.1 years, respectively in the overweight and obese groups, and those in normal group and thin group was 4.7 and 4.5 years, 4.6 and 4.7 years, respectively. Conclusions:The ages of sexual characteristics development and menarche tend in Tongzhou District of Beijing to be earlier than that being reported of Beijing's survey 20 years ago. Girls characterized as overweight and obese not only start puberty at an earlier age than girls of normal weight, but also have a shorter developmental process.

Objective:To establish the reference values and growth curves of weight/length, body mass index, and ponderal index for Chinese newborns with gestational ages of 24 to 42 weeks, in order to provide a reference for the assessment of body proportionality and nutritional status at birth.Methods:Cross-sectional study design was applied. From June 2015 to November 2018, a total of 24 375 singleton live birth newborns with gestational ages of 24 to 42 weeks from 13 cities including Beijing, Harbin, Xi′an, Shanghai, Nanjing, Wuhan, Guangzhou, Fuzhou, Kunming, Tianjin, Shenyang, Changsha, and Shenzhen were selected, excluding those impacting the establishment of the reference values. The generalized additive model for location, scale, and shape (GAMLSS) was employed to establish percentile (P 3, P 10, P 25, P 50, P 75, P 90, P 97) reference values and growth curves of weight/length, body mass index, and ponderal index for male and female newborns with gestational ages of 24 to 42 weeks. The established growth standards in this study were compared with the standards from the 1988 Chinese data, the INTERGROWTH project, and the USA reference values. Results:A total of 24 375 newborns with 12 264 preterm newborns (7 042 males and 5 222 females) and 12 111 full-term newborns (6 155 males and 5 956 females) were included in this study. The percentile reference values and growth curves of weight/length, body mass index, and ponderal index were obtained for male and female newborns with gestational ages of 24 to 42 weeks. Weight/length of males in all gestational ages at P 10, P 50 and P 90 was 0 to 0.2 kg/m higher than that of females, and body mass index of males in all gestational ages at the P 10, P 50 and P 90 was 0.1 to 0.3 kg/m 2 higher than that of females. The established growth curves of weight/length and body mass index at the upper percentile and ponderal index at both upper and lower percentiles were greatly different from those of the 1988 Chinese data, which, for example, reported the difference ranges at P 90 as -1.09 to 0.40 kg/m for weight/length, -1.19 to 0.92 kg/m 2 for body mass index, and -0.64 to 0.81 kg/m 3 for ponderal index. The established weight/length curves were generally consistent with the reference values from the INTERGROWTH project with a difference of -0.17 to 0.20 kg/m at P 50, while being 0.02 to 0.40 kg/m lower at P 90 and 0.13 to 0.41 kg/m higher at P 10 than that of the INTERGROWTH reference values at gestational ages of ≤32 weeks. The established body mass index curves differed from that of the USA reference values with a difference of -0.47 to 0.17 kg/m 2 at P 50, while being 0.53 to 1.10 kg/m 2 lower at gestational ages of ≥37 weeks but 0.17 to 0.45 kg/m 2 higher at gestational ages of ≤28 weeks than that of the USA reference values at P 90. Conclusion:The establishment of the new standardized growth reference values of weight/length, body mass index, and ponderal index for Chinese newborns by different gestational ages are useful for clinical practice and scientific research.

Objective:To analyze the influential factors of stunting among children under 7 years of age in nine cities of China in order to provide empirical data for early prevention and intervention for stunting.Methods:The survey was carried out with 1∶1 case-control study design in the communities and kindergartens of nine cities (Beijing, Harbin, Xi′an, Shanghai, Nanjing, Wuhan, Guangzhou, Fuzhou, and Kunming) from June to November in 2016. Children of heights lower than the 3 rd percentile according to the 2009 children′s height standard in China were included as the stunting case group ( n=1 281), and those with normal height matched for geolocation, gender, and age were recruited as the control group ( n=1 281). The height and weight were measured on site, and the information related to family, perinatal status, diet and feeding, lifestyle, and medical history was collected by questionnaire. Continuous variables were compared by paired samples t test and Wilcoxon matched-pair signed ranks test, and proportions were compared by paired Chi square test. Multivariate analysis were carried out using conditional Logistic regression model. Results:Among 1 281 pairs of stunting and control group, there were 677 pairs of boys and 604 pairs of girls, with 238 pairs of children under age 3 years and 1 043 pairs of children aged 3 to 7 years. The Z scores for height and weight of stunting group were lower than that of control group (-2.27 (-2.54, -2.08) vs. -0.59 (-1.04, -0.10), -1.85 (-2.35, -1.38) vs. -0.69 (-1.20, -0.21), Z=30.982, 25.580, both P<0.01). Among family related factors, parental education level, height, weight, and height of grandparents in stunting children were all lower than those in control group (all P<0.05). Among individual related factors, proportion of preterm birth, low birth weight, shorter birth length, mother's pregnancy complications, difficulties adding milk or complementary feeding, poor appetite, slow eating, picky and partial eating, passive eating, more snack intake, shorter sleep duration, difficulty falling asleep, disturbed sleep, and recurrent infectious diseases in infant in stunting children were all higher than those in control group (all P<0.05). Multivariate Logistic regression analysis results illustrate that the lower the parental education level and the parental height, the higher the risk of stunting. For example, the risk of stunting in children whose fathers had short stature was 6.46 times (95% CI: 2.73-15.30) of those children whose fathers′ height were medium and the risk of stunting in children whose mothers were short stature was 10.56 times (95% CI: 4.92-22.69) of those children whose mothers′ height were medium. The risks of stunting increase significantly among preterm children or those with low birth weight ( OR=2.27, 95% CI: 1.33-3.88), birth length<45 cm ( OR=3.56, 95% CI: 1.41-8.98), difficulties adding milk or complementary feeding ( OR=2.04, 95% CI: 1.32-3.15), poor appetite ( OR=3.20, 95% CI: 1.74-5.89), slow eating ( OR=1.85, 95% CI: 1.31-2.63), and food allergy ( OR=1.80, 95% CI: 1.02-3.16). Conclusion:Parental short stature, preterm birth or low birth weight, shorter birth length, feeding difficulty in infant, poor appetite, slow eating, and food allergy are the main risk factors for stunting in infants and children.

Objective: To survey the children under 7 years of age in nine cities of China for a better understanding of the current situation of childhood stunting. Methods: According to a stratified cluster sampling design, a cross-sectional survey on children under 7 years of age was carried out in 9 cities (Beijing, Harbin and Xi′an in northern China; Shanghai, Nanjing and Wuhan in central China; and Guangzhou, Fuzhou and Kunming in southern China) from June to November in 2016. A total of 110 499 children were recruited. Height of children was evaluated using the growth standards for Chinese children (2009 edition) .Children with height less than the 3rd percentile of the growth standards were considered as stunting, and children with height between the 3rd and 10th percentiles of the growth standards were considered as relatively short stature. Chi-square test was used for comparison between data of boys and girls, urban and suburban, as well as among different ages and regions. Results: Totally 113 084 children under 7 years of age should be investigated and actually 110 499 children were investigated, with a rate of 97.7%. The prevalence of stunting was 1.9% (2 141/110 499) among all the children. The prevalence of stunting in urban children (1.6%, 904/55 524) was lower than that in suburban children (2.3%, 1 237/54 975, χ²=56.246, P<0.01). The gender difference in stunting prevalence was not statistically significant (1.9% (1 121/57 921) in boys and 1.9% (1 020/52 578) in girls, χ²=0.003, P=0.965). The prevalence of stunting decreased with age for children younger than 3 years, from 1.8% (312/17 080) in 0-<1 year of age group to 1.2% (168/13 740) in 2-<3 years of age group, but increased to 2.2% (240/11 073) at 6-<7 years group. Comparison among different regions showed that the stunting prevalence in southern region was higher than those in the central and northern regions (0.9% (193/20 374) in northern urban, 0.8% (154/18 486) in central urban, and 3.3% (557/16 664) in southern urban children), showing a statistical significance (χ²=437.736, P<0.01); 1.1% (241/21 924) in northern suburban, 1.4% (227/16 775) in central suburban and 4.7% (769/16 276) in southern suburban children, showing a statistical significance (χ²=646.533, P<0.01). In urban areas, the difference between the central and northern regions showed no statistical significance (χ²=1.429, P=0.232) and the stunting prevalence of central Chinese children was slightly higher than that of northern Chinese children in suburban areas (χ²=5.130, P=0.024). Among the nine cities, the stunting prevalence of Guangzhou (6.1%, 613/10 019) was higher than those of other cities (χ²=1 559.64, P<0.01). Among the stunting children, 78.4% (1 679/2 141) were classified as borderline or mild and only 7.2% (154/2 141) were classified as severe. The prevalence of relatively short stature was 5.2% (5 721/110 499). Conclusions The prevalence of stunting among children under 7 years of age in nine cities of China is low and most of the stunting children were classified as mild; the prevalence of stunting in suburban children is higher than that in urban children; the gender difference show no statistical significance; and the prevalence of stunting in southern Chinese children is higher than those in central and northern Chinese children.

Objective: To investigate the timing of permanent tooth emergence and its association with physical growth among children aged 4-7 years in 9 cities of China, and to analyze the trend of permanent teeth development. Methods: According to a stratified cluster sampling design, a cross-sectional survey on the timing of permanent tooth emergence children aged 4-7 years was carried out in 9 cities (Beijing, Harbin and Xi′an in northern China; Shanghai, Nanjing and Wuhan in central China; Guangzhou, Fuzhou and Kunming in southern China) from June to October in 2015. A total of 37 973 children (19 035 boys and 18 938 girls) were recruited and were divided into different age groups (4.0-<4.5, 4.5-5.0, 5.0-5.5 and 6.0-<7.0 years of age). The situation of the exfoliation of primary teeth and the eruption of permanent teeth were investigated. Height and weight were measured using the standardized methods. Z-scores of physical growth indicators were calculated using the growth standards for Chinese children in 2009. Probit regression analysis was used to determine the median and percentile age of transition from deciduous to permanent teeth. Chi-square test was used for comparison of categorical data and t test was used for comparison of measurement data between boys and girls, urban and suburban as well as among different ages and regions. Meanwhile, the data from the national survey on physical growth and development of children under 7 years of age in 9 cities of China in 1995 were used to analyze the trends of the permanent teeth development. Results: The rate of transition from deciduous to permanent teeth in 37 973 children aged 4-7 years was higher with age, which was 0.6% (42/7 568) in 4.0-<4.5 years of age group, 30.3% (2 295/7 583) in 5.5-<6.0 years of age group, and 74.5% (5 680/7 627) in 6.0-<7.0 years of age group. The rates of transition from deciduous to permanent teeth in boys were all lower than those of girls except for children aged 4.0-<4.5 years (all P<0.01). The rate of transition from deciduous to permanent teeth in urban children was higher than that in suburban children for older than 5.5-6.0 years of age group in boys and older than 4.5-5.0 years of age group in girls, which was 74.2% (1 427/1 924) in urban boys aged 6.0-<7.0 years and 69.2% (1 305/1 885) in suburban boys aged 6.0-<7.0 years (χ²=11.446, P<0.01). The age of transition from deciduous to permanent teeth was 6.00 (95%CI: 5.98-6.01) years and the range of the 3-97 percentile was 4.88-7.11 years of age. The median permanent tooth emergence age of girls was lower than that of boys (5.94 vs. 6.06 years) and the median age of urban children was lower than that of suburban children (5.94 vs. 6.05 years). The median permanent tooth emergence age of southern Chinese children (6.05 years) was higher than that of northern (5.97 years) and central Chinese children (5.97 years). The weight for age Z-scores (WAZ), height for age Z-scores (HAZ) and body mass index for age Z-scores (BMIZ) of children with transition from deciduous to permanent teeth (0.35±1.17, 0.32±1.00, 0.23±1.16) were significantly higher than those of children without transition from deciduous to permanent teeth (0.03±1.13, 0.03±1.02, 0.04±1.13, t=20.81,21.67,12.09, all P<0.05). In comparison with the data in 1995, data in 2015 showed that the rate of transition from deciduous to permanent teeth was higher, for example, the rate of urban boys aged 6.0-<7.0 years group was 63.8% (1 146/1 796) in 1995, and increased to 74.2% (1 427/1 924) in 2015 (χ²=46.748, P<0.01). The median permanent tooth emergence age decreased by 0.24 years in 2015 as compared with that in 1995. Conclusions The development of permanent teeth is earlier in girls than in boys, earlier in urban children than in suburban children and slightly delay in southern children than in central and northern Chinese children. In addition, the development of permanent teeth, which is related to the physical growth, slightly accelerate in China during the past 20 years.

Objective:To study and establish the percentile reference values of waist circumference (WC) for Chinese children aged 3-7 years.Methods:A total of 26 480 children aged 3-7 years were collected as part of the National Survey on Physical Growth and Development of Children in nine cities (Beijing, Harbin, Xi’an, Shanghai, Nanjing, Wuhan, Guangzhou, Fuzhou and Kunming) in China from June to November 2015. Sex- and age-specific smoothed percentile reference values of WC were established using the Lambda Mu Sigma method. The P 75 and P 90 curves of WC for children aged 3-7 years in this study were linked with the published P 75 and P 90 cut-off points for Chinese children and adolescents aged 7-18 years. The P 50 percentile of WC in this study was compared with the corresponding percentiles of several foreign studies. Results:The P 5, P 10, P 15, P 20, P 25, P 50, P 75, P 80, P 85, P 90 and P 95 reference values of WC were obtained for boys and girls aged 3-7 years biannually, at the interval of every six months. Results showed that WC at the P 50 had significantly increased from 47.5 cm at the age of 3 to 54.2 cm at the age of 7 for boys and from 47.0 cm at the age of 3 to 52.2 cm for girls at the age of 7. The corresponding WC percentile values appeared a bit higher in boys than those in girls at the same age, with the differences from 0.4 to 3.6 cm. The differences between measured and fitted WC at each empirical percentile ranged from -0.3 to 0.5 cm for both boys and girls aged 3-7 years. The P 75 and P 90 values of WC for boys and girls aged 3-7 years in this study presented a consistent, continuous tendency on age with the published WC cut-off points ( P 75 and P 90) for Chinese children and adolescent aged 7-18. The increasing trend of WC by age in Chinese children aged 3-7 years was consistent with those of foreign studies, at the middle level for boys and lower middle level for girls. Conclusions:Through this study, we established the WC percentile values for Chinese children aged 3-7 years and achieved the continuity in age with the published WC cut-off points for Chinese children and adolescents aged 7-18. These established WC percentile values can be used as reference for clinical practice, health care and scientific research.

Objective: To develop the reference values of carotid intima-media thickness (cIMT) in Chinese children aged 6-11 years. Methods: A convenient cluster sampling method was used to conduct a cross-sectional survey from November 2017 to January 2018 in a primary school in Huantai County, Zibo City, Shandong Province. A total of 1 033 children aged 6-11 years (excluding children with obesity or hypertension) were included. Percentile curves for cIMT were drawn using the lambda, mu and sigma (LMS) method. Results: This study developed the cIMT reference values (P₉₀ and P₉₅) for sex and age aged 6-11 years, including P₉₀ and P₉₅ reference values of mean cIMT, left cIMT and right cIMT, respectively. With the increase of age, the cIMT percentile values also increased. For the same age and the same percentile, the cIMT values of boys were higher than those of girls. Conclusion This study developed sex-specific and age-specific cIMT percentile reference values in children aged 6-11 years.

Objective: To develop and validate a simplified height-specific blood pressure cutoffs table for screening hypertension in Chinese children and adolescents. Methods: We developed a simplified height-specific blood pressure cut offs table according to Chinese Blood Pressure Reference for Children and Adolescents aged 7-18 years (WS/T 610-2018) (hereafter referred to as "complex definition"). Populations from Early Warning, Diagnosis and Treatment of Children Cardiovascular Disease Project ("Ji′nan sample") and Shandong Children Cardiovascular Cohort Study Project ("Zibo sample") were used as validation populations for evaluating the screening effect of the simplified table for elevated blood pressure and hypertension in children and adolescents. Results: We developed simplified height-specific blood pressure cutoffs table including 7 height groups and 28 cutoffs. Both Ji′nan and Zibo samples were selected by convenient sampling method, and the former included 7 233 participants aged 7 to 17 years, among whom 3 790 (52.4%) were boys. Latter population included 1 277 participants aged 7 to 11 years, among whom 681 (53.3%) were boys. The simplified table performed well for identifying elevated blood pressure in Ji′nan sample, with values of area under the receiver operating curve (AUC) (95%CI), sensitivity, specificity, and Kappa statistic as 0.96 (0.95-0.97), 93.0%, 98.5% and 0.91, respectively, which were similar with results in Zibo sample [the values were 0.92 (0.90-0.95), 87.0%, 98.0% and 0.85, respectively]. The simplified table also performed well for identifying hypertension in Ji′nan sample with values of AUC (95%CI), sensitivity, specificity, and Kappa statistic as 0.92 (0.91-0.94), 86.9%, 98.1% and 0.85, respectively, which were similar with results in Zibo sample [the values were 0.94 (0.91-0.96), 88.2%, 98.9% and 0.88, respectively]. Conclusion Screening for elevated and high blood pressure based on simplified height-specific blood pressure cutoffs table is easy to use and it shows satisfying effect.

Objective: To investigate the status of the development of primary teeth and to identify the development patterns among infants and toddlers in nine cities of China in 2015. Methods: Healthy children aged 1-<36 months were investigated by across-sectional survey and retrospective studies, which was carried out in 9 cities (Beijing, Harbin and Xi′an in northern China; Shanghai, Nanjing and Wuhan in central China; and Guangzhou, Fuzhou and Kunming in southern China) from June to October in 2015. Subjects (n=103 995) were divided into 14 age groups (1-<2, 2-<3, 3-<4, 4-<5, 5-<6, 6-<8, 8-<10, 10-<12, 12-<15, 15-<18, 18-<21, 21-<24, 24-<30, 30-<36 months). There were 150-200 boys and girls respectively in each group of urban and suburb areas in each city. The eruption status and the number of primary teeth were examined by the trained child health care physician or pediatrician on the spot. The timing of primary teeth eruption of children was retrospectively surveyed using a questionnaire. The prevalence of primary teeth was calculated and χ² test was used for comparison of categorical data. Probit regression analysis was used to determine the median and percentile age of eruption of primary teeth. Results: Totally 103 995 children aged 1-<36 months were investigated. There were 52 346 children in urban areas (boys 26 228, girls 26 118) and 51 649 children in suburb areas (boys 25 912, girls 25 737). The eruption rate of primary teeth in children under 2 years became higher with age and the difference among each age group was statistically significant (χ²=85 913.868, P<0.01), which was 0.3% (22/7 450) in 3-<4 months group, 43.0% (3 227/7 503) in 6-<8 months group and 99.9% (7 441/7 446) in 15-<18 months group. The eruption age of primary teeth was 6.6 months (95%CI: 6.5-6.7 months), and the range of the 3rd to 97th percentile was 4.1-10.6 months. The eruption ages of primary teeth in urban and suburb areas children were 6.6 months (95%CI: 6.5-6.7 months) and 6.6 months (95%CI: 6.5-6.7 months) respectively. The eruption age of primary teeth was earlier in boys (6.4 months, 95%CI: 6.3-6.5 months) than that in girls (6.7 months, 95%CI: 6.6-6.8 months). The median eruption age of primary teeth was earlier in northern China (6.2 months) than that in central (6.7 months) and southern China (6.9 months). The eruption rate of primary teeth became higher with age, showing that the median number of primary teeth was 2 in 8-<10 months group, 8 in 12-<15 months group and 20 in 30-<36 months group. Conclusions The timing of eruption of primary teeth was similar between urban and suburb areas children and that of the boys was slightly earlier than that of the girls. There were slight differences among different regions in the eruption timing of primary teeth. The range of the 3rd to 97th percentile in the eruption age of primary teeth was 4.1-10.6 months and the number of primary teeth followed the regular development pattern with age.