Objective: To explore the influence of birthweight and delivery mode on overweight/obesity and abdominal obesity in primary school students, and to provide evidence for childhood obesity prevention. Methods: After physical examination, questionnaire survey was conducted among 3 361 students and their parents from 3 primary schools in Guangzhou selected through stratified clustering sampling. Information about birthweight and delivery mode was collected. Logistic regression model was used to analyze the association of birthweight and delivery mode with overweight/obesity and abdominal obesity. The multiplicative interaction term and the Delta method was used to explore the potential interaction. Results: The prevalence rate of overweight and obesity for primary school students was 21.33%, and the rate of abdominal obesity was 12.08%. Multivariate Logistic regression analysis showed that delivery by cesarean section was associated with 44% increased risk of overweight/obesity(OR=1.44, 95%CI=1.16-1.80), as compared to vaginal delivery. Higher birthweight was linked to increased risk of overweight/obesity(OR=1.62, 95%CI=1.09-2.42). There was no significant association of birth weight and delivery mode with abdominal obesity in multivariate analysis(P>0.05). Additionally, a positive additive interaction was seen between delivery mode and parental obesity for students risk of overweight/obesity(RERI=0.33, 95%CI=0.02-0.65), as well as for the risk of abdominal obesity(RERI=0.39, 95%CI=0.12-0.65). Conclusion Cesarean section delivery and higher birthweight are linked to increased risk of overweight and obesity in primary school students. The synergistic effect of cesarean section and parental obesity may increase the risk of childhood obesity.

Objective: To investigate the effect of maternal passive smoking during pregnancy and girls’ overweight /obesity on the age at menarche(AAM), and to provide a reference for improving healthy development of children and adolescents. Methods: Based on the school entrance physical examination in 2016, a cross-section study was conducted by convenient sampling method, in a total of 2 722 students of 7th grade, from 26 middle schools in urban areas of Guangzhou. Multivariate logistic regression model was used to investigate the relationship between maternal passive smoking during pregnancy and girls’ overweight /obesity and AAM. A four-way decomposition method was used to explore the mediated effect of girls’ overweight/obesity on the relationship between maternal passive smoking during pregnancy and AAM. Results: The proportion of girls who had menstruate was 90.82%(2 472/2 722). The median AAM was 12.00 years old, with an early menarche rate of 34.91%(863/2 472). Compared with girls whose mother hadn’t passive smoking during pregnancy, the risk of early AAM in girls with mother passive smoking during pregnancy≤3 days/week increased by 32%(OR=1.32, 95%CI=1.06-1.65), the risk in girls with maternal passive smoking during pregnancy>3 days/week increased by 58%(OR=1.58, 95%CI=1.21-2.07). Multivariate Logistic regression analysis showed that, overweight or obesity girls had a 77% higher risk of early AAM than non-overweight/obesity girls(OR=1.77, 95%CI=1.36-2.31). The four-way decomposition analysis showed 79.60% of early AAM risk could be accounted by maternal passive smoking during pregnancy(P<0.01). Conclusion Girls’ overweight/obesity and maternal passive smoking during pregnancy were associated with early menarche. The effect on daughters’ age at menarche is mainly in a direct effect manner of maternal passive smoking during pregnancy.