Abstract With the amendment of China s family planning, the number of firstborn children has increased gradually, thus resulting in only children transitioning to non only children. The emotional changes and the mental and behavioral problems faced by these firstborn children have begun to receive extensive attention among scholars and society. Childhood emotional and behavioral problems can affect later adult life, such as by increasing the risk of maladjustment and peer rejection in adulthood. Research using innovative study designs is crucial to examine firstborn children s emotional and behavioral problems, and the factors influencing these problems. Empirical research on interventions will be highly important to ensure a healthy transition of firstborn children from only children to non only children.

Objective: This study systematically reviewed the findings of studies on the factors influencing emotional and behavioral problems among firstborn children in transition to siblinghood, to provide a theoretical basis for the study of emotional behavior in firstborn children during role transition. Methods: CBM, VIP, CNKI, WanFang Data, PubMed, Web of Science, OVID and EBSCO were electronically searched to collect studies on the relevant factors influencing the emotional and behavioral characteristics of firstborn children in transition to siblinghood (TTS) from inception to March 3rd, 2021. Literature screening and data extraction were conducted by two independent authors to evaluate the risk of bias in the included studies. The results of the included studies were summarized by qualitative analysis. Results: A total of nine studies were included, comprising four prospective cohort studies and five cross sectional studies. Systematic evaluation results indicated three main types of factor associated with behavioral problems among firstborn children:factors of firstborn children (gender, age and temperament), family factors (parents upbringing, family relationships, family environment, social economy, maternal behavior and whether firstborn children knew that the second children would arrive), and social factors (relationships between teachers and students, peer relationships and life changes). The main factors affecting emotions were their own factors (age and self acceptance). Negative temperament in firstborn children, negative parenting styles, negative family relationships and family environments, prohibited behaviors among mothers, whether the firstborn children were informed of the arrival of the second children during pregnancy, poor relationships between teachers and students, peer relationships and life changes may increase the risk of emotional and behavioral problems among firstborn children. Whether other factors might have affected the results of the study is unclear. Conclusion Important factors influencing firstborn children s emotions and behaviors during TTS, must be confirmed through a high quality prospective cohort study. Intervention studies may be appropriate to verify the results and provide an empirical basis for behavioral interventions in firstborn children with different emotional problems.

Objective: This study explored the predictive effects of psychological stress in early and middle puberty on subsequent emotional and behavioral problems. Methods: A cohort of 911 boys and girls from primary and secondary schools in Chongqing was studied. Psychological stress was measured in early and middle adolescence, and the levels of emotional and behavioral problems were determined in one year follow up. Logistic regression analysis was used to analyze the effects of psychological stress in early and middle adolescence on subsequent emotional and behavioral problems. Results: The average psychological stress score in early and middle adolescence was (27.96±24.95), and the average scores of internalized and externalized behavioral problems and overall problems one year later were (8.21±8.46)(6.21±5.87) and (37.90±24.68) respectively. When grouped by gender, these scores, as well as the detection rate of anxiety and depression, withdrawal, physical discomfort, thinking problems, internalization problems and overall problems, were higher in girls than boys (t/Z=-6.38，-5.63，-6.06，-3.74，-6.80，-5.47， χ 2=15.88，12.01，3.92，6.64，24.67，15.88， P <0.05). Logistic regression showed that the psychological stress scale score was a risk factor for internalized and externalized behavioral problems and overall problems( P <0.05). Conclusion Psychological stress levels in early and middle puberty have a positive predictive effect on emotional and behavioral problems in the following year.

Objective: To explore whether psychological stress in early and mid puberty is predictive of adolescent healthrisk behaviors. Methods: In April 2018, a total of 1 046 primary and secondary school students from grade 5 to 8 were recruited through purposive sampling. The basic information and psychological stress of the respondents were collected by questionnaire and physical examination. In addition, self reports of health risk behaviors were collected in October 2018. Logistic multiple regression analysis was used to analyze the relationship between psychological stress and health risk behaviors of adolescents. Results: The reported health risk behaviors of the surveyed adolescents ranking from high to low were unreasonable physical activity (62.05%), food preferences (24.76%), fighting (21.03%), suicidal ideation (17.02%), ideation of running away from home (9.85%), low mood (8.80%), smoking (4.21%), drinking (3.73%), gambling (3.63%) and internet addiction (3.06%). Logistic multiple regression analysis showed that the high level of psychological stress was a risk factor for fighting ( OR =1.02, 95% CI =1.01-1.03), suicidal ideation ( OR =1.02, 95% CI =1.01-1.03), low mood ( OR =1.02, 95% CI =1.01-1.03), ideation of running away from home ( OR =1.02, 95% CI =1.01-1.03), unreasonable physical activity ( OR =1.01, 95% CI =1.00-1.02), smoking ( OR =1.02, 95% CI = 1.00-1.03), internet addiction ( OR =1.02, 95% CI =1.00-1.03), food preferences ( OR =1.01, 95% CI = 1.00-1.02) and gambling ( OR =1.02, 95% CI =1.01-1.04)( P <0.05). Conclusion Unreasonable physical activity and food preferences are most common health risk behaviors among adolescents. Psychological stress during early to middle puberty is predictive of adolescent health risk behaviors.

Objective: To explore the status of depressive symptoms among adolescents in different pubertal stages in a district of Chongqing. Methods: A self designed questionnaire and Children s Depression Inventory were administered among 1 001 students in a district of Chongqing. Score and associated factors of depressive symptoms of adolescents through descriptive statistical analysis, Chi square test, analysis of variance and Logistic regression analysis. Results: The detection rate of depressive symptoms among adolescents in a district of Chongqing was 17.3%, and the total score of depression scale was (12.02±6.72). There were statistically significant differences in the inefficiency subscale score of boys across stages of genital, pubic hair, armpit hair and beard, and whether the first spermatorrhea has occurred( t/F =7.08，5.46，5.18，4.21，5.84， P <0.05), while significant differences were found in the anhedonia and inefficiency subscales scores among girls across different stages of breast, pubic hair and armpit hair, and whether menarche has occurred( t/F =19.43，4.92，3.98，7.35， P <0.05). Multivariate Logistic regression analysis showed that the absence of first spermatorrhea and menarche were associated with lower prevalence of depressive symptoms in boys and girls ( OR=0.60, 95%CI=0.36-0.98; OR=0.46, 95%CI =0.22-1.00), while pubic hair development was associated with higher prevalence of depressive symptoms in girls ( OR=9.58, 95%CI =1.28- 71.71 ). Conclusion The detection rate of depressive symptoms among adolescents is relatively low. Boys who have had the first spermatorrhea, and girls with advanced pubic hair development or have had menarche are more likely to suffer from depressive symptoms.

Objective: To explore the relationship between the emotional and behavioral problems and family relations of firstborn children from an urban area of Chongqing during the role transition period, to provide a scientific basis for creating a good family relationship and to reduce the occurrence of children s emotional behavior problems. Methods: Totally 1 359 mothers of children in the role transition period were recruited from obstetric clinics at two Grade A hospitals in Chongqing, and mothers with informed consent using self designed questionnaire and parental version of the Child Behavior Checklist (CBCL). It was analyzed the association between family relationships and the emotional/behavioral problems of firstborn children of different ages. SPSS statistical software (version 20) was used for the descriptive statistical analysis, chi square test, and multiple linear regression analysis. Results: The parental relationship (56.6%), mother child relationship (80.4%) and father child relationship (64.9%) of most firstborn children was good, and 61.7% of families enjoyed a harmonious atmosphere. For the age groups 1.5-5 years and 6-13 years, the respective CBCL total scores were (18.22±13.63) and (24.20±17.52), and the detection rates were 10.7% and 10.5%, respectively. The results of the multiple linear regression analysis showed that, for both age groups, firstborn children who had good parental relationships, good mother child relationships, good father child relationships, and a harmonious family atmosphere exhibited fewer internalizing, externalizing and overall emotional behavior problems ( P <0.05). Conclusion The total detection rate of emotional and behavioral problems among firstborn children in the role transition period, which is low. Good parental relationships, good parent child relationships, and a harmonious family atmosphere are protective factors against emotional and behavioral disorders in firstborn children during the role transition period.

Objective: To compare the emotional and behavioral characteristics of preschool firstborn children across the transition to siblinghood with the only children in a district of Chongqing. Methods: Data were derived from a cohort study on firstborn children transition to siblinghood. Totally 882 firstborn children (3.58±1.25) years old and 329 only children (3.98±1.02) years old were recruited from two hospitals and 19 kindergartens in a district of Chongqing, respectively. Their mothers filled out the parental version of Child Behavior Checklist (CBCL) and self designed questionnaire. Results: The overall scores of emotional and behavioral problems of firstborn children and only children were (25.17±18.82) and (31.75±18.64). The results of rank sum test showed that the scores of the firstborn children in all dimensions, internalizing and externalizing behavior problems and overall emotional and behavioral problems were lower than those of the only children ( P <0.05). Chi square test results showed that the detection rates of internalizing, externalizing and overall emotional behavior problems in only children(12.77%, 13.07%, 14.59%) were higher than those in firstborn children(8.28%, 8.28%,8.16%) ( χ 2=5.62, 6.36, 11.09, P <0.05). Multiple linear regression showed that after adjusting for age, gender, family economic pressure, temperament type of children, family atmosphere and family type, the scores of internalizing problems, externalizing problems and overall problems of the only children were still higher than those of the firstborn children ( B =1.54, 2.32, 6.81, P <0.05). Conclusion The firstborn children across the transition to siblinghood show less emotional and behavioral problems than the only children, and the scores and detection rates of all types of emotional and behavioral problems of the firstborn children are lower than those of the only children.

Objective: To explore the influence of parental company before and after having second child on the emotional and behavioral problems of preschool firstborn children, and to provide a reference for emotional problems prevention of firstborn children. Methods: Questionnaire survey was conducted among mothers of firstborn children who met the inclusion and exclusion criteria from two Grade A hospitals in Chongqing from March to December 2019. The average age of 845 firstborn children was (3.56±1.24) years old. The chi square test was used to compare the general characteristics and parent company of boys and girls. Rank sum test was used to compare the differences of emotional and behavioral problems of firstborn children with different parents company. Multiple linear regression models were used to compare the differences of internalizing, externalizing and total problems in firstborn children with different parents company. Results: After having the second child, parents spent less time with their firstborn children, among which the decrease of the accompanying time of the mother and the total accompanying time of the parents were statistically significant( Z =3.76, 2.86, P <0.05). The scores of internalizing problem were higher when the mother s company time decreased ( B=1.18, 95%CI = 0.01 -2.36) and the parents total company time decreased( B=1.41, 95%CI =0.33-2.48). The scores of the externalizing problem ( B=1.25, 95%CI =0.10-2.39) and the total problem ( B=4.31, 95%CI =1.05-7.57) with the decrease of parents total company time were higher. Conclusion Parent company has an important influence on the emotional and behavioral problems of firstborn children. Firstborn children whose parents accompanying time decreases after having second children scored higher on emotional and behavioral problems.

Objective: To explore the association between different family factors and children’s puberty timing, and to provide a reference for further research on puberty development of children. Methods: A prospective cohort study was conducted on a total of 1 237 children in one district, Chongqing, using targeted sampling. Cox regression was used to analyze the association between family factors and the puberty timing of children. Results: The results of univariate analysis showed that baseline age and BMI were risk factors of early puberty timing in boys and girls (P<0.01). Breast development (HR=1.27, 95%CI=1.04-1.54) was observed earlier in vaginal delivery than in cesarean section. Self-conscious family economic condition is good is the protective factor for the early timing of girl’s menstruation (HR=0.81, 95%CI=0.66-0.99), pubic hair development(HR=0.80, 95%CI=0.65-0.97) and the boy’s puberty development (Testicular development HR=0.69, 95%CI=0.58-0.83, first ejaculation HR=0.62, 95%CI=0.49-0.78, external genitalia development HR=0.70, 95%CI=0.56-0.87, pubic hair development HR=0.66, 95%CI=0.54-0.80). The left-behind boys later observed testicular development (HR=0.74, 95%CI=0.57-0.96), first ejaculation (HR=0.71, 95%CI=0.50-0.99) and pubic hair development (HR=0.68, 95%CI=0.51-0.91). Testicular development (HR=1.26, 95%CI=1.01-1.58) was observed earlier in boys who felt their parents were close (P<0.05). The results of multivariate analysis showed that the timing of pubic hair development was later in floating girls (HR=0.79, 95%CI=0.65-0.96), and family factors had nothing to do with the puberty timing in boys. Conclusion In the study, left behind children, self-perceived of parents relationship and family economic conditions are the influencing factors of children’s puberty timing. However, after adjusted for age and BMI, this association was mainly found in pubic hair of girls. The association between family factors and other pubertal development events still needs to be confirmed by further follow-up investigation.

Objective: To analyze the characteristics of puberty growth of boys and to explore the relationship between puberty growth and sexual development of boys. Methods: Pubertal development of boys from grade 1 to grade 4 in Jiulongpo district of Chongqing was followed up once every six months. The data of height, weight, BMI, the age of first ejaculation and testicular development of boys from baseline to follow-up every 6 months for 5 years were analyzed. Based on peak height velocity (PHV), the average level of PHV and age at peak height velocity(PHA) were analyzed. ANOVA was used to compare the height growth rate of boys in different age groups before and after the first ejaculation. Kendall rank correlation was used to analyze the relationship between different stages of testicular development and BMI. Results: The mean age of PHA was (11.72±1.03) years in adolescent height speed cohort, and the mean age of first ejaculation was (12.45±0.98) years before and after the first ejaculation cohort. There was significant difference in the increment of height before and after one year of the age of first ejaculation (P<0.05), the younger the age of the first ejaculation, the greater increase of height in the following year. The height, weight, BMI of boys aged 11 to 14 years were positively correlated with testicular volume(P<0.05). Conclusion The height growth of boys reached its peak one year before the first ejaculation, and began to decrease after first ejaculation, and the age of the first ejaculation of boys was negatively correlated with the increment of height in the following year, while the testicular development of boys was positively correlated with height, weight and BMI.