Impact of the Korea Early Childhood Home-visiting Intervention

Home environment as assessed using IT-HOME (Infant-Toddler Home Observation for Measurement of Environment) when the child is 6 months old. IT-HOME (Infant-Toddler Home Observation for Measurement of Environment), composed of 45 items, was developed by Caldwell & Bradley (1984). The minimum score is 0 and the maximum score is 45, and a higher score means a better outcome.

Home environment as assessed using IT-HOME (Infant-Toddler Home Observation for Measurement of Environment) when the child is 12 months old. IT-HOME (Infant-Toddler Home Observation for Measurement of Environment), composed of 45 items, was developed by Caldwell & Bradley (1984). The minimum score is 0 and the maximum score is 45, and a higher score means a better outcome.

Home environment as assessed using IT-HOME (Infant-Toddler Home Observation for Measurement of Environment) when the child is 24 months old. IT-HOME (Infant-Toddler Home Observation for Measurement of Environment), composed of 45 items, was developed by Caldwell & Bradley (1984). The minimum score is 0 and the maximum score is 45, and a higher score means a better outcome.

Number of emergency department visits due to injuries when the child is 6 weeks old.

Number of emergency department visits due to injuries when the child is 6 months old.

Number of emergency department visits due to injuries when the child is 12 months old.

Number of emergency department visits due to injuries when the child is 24 months old.

Child development as assessed using the K-Bayley-III (Korean Bayley Scales of Infant and Toddler Development-III) score when the child is 24 months old

Breastfeeding duration when the child is 6 weeks old.

Breastfeeding duration when the child is 6 months old.

Maternal self-rated health when the child is 12 months old.

Breastfeeding duration when the child is 24 months old.

Maternal self-rated health when the child is 6 weeks old.

Maternal self-rated health when the child is 6 months old.

Maternal self-rated health when the child is 12 months old.

Maternal self-rated health when the child is 18 months old.

Maternal self-rated health when the child is 24 months old.

Community service linkage as measured by the number of community services a mother has received during the last year when the child is 12 months old.

Community service linkage as measured by the number of community services a mother has received during the last year when the child is 24 months old.

School readiness as assessed using the Korean Early Development Instrument (EDI) administered by the child's teacher. The EDI evaluates children's overall developmental readiness for school across five domains: (1) Physical Health and Well-being, (2) Social Competence, (3) Emotional Maturity, (4) Language and Cognitive Development, and (5) Communication Skills and General Knowledge. The assessment consists of approximately 100 items based on teacher observations and takes 15-20 minutes per child to complete.

Child intelligence assessed using the Wechsler Preschool and Primary Scale of Intelligence (WPPSI-IV) administered by trained occupational therapist. The assessment measures overall intellectual ability and cognitive development.

Number of child abuse reports obtained through secondary data linkage with the Social Security Information Service's child abuse reporting database.

Number of emergency department visits due to injuries (indirect indicator of child abuse) obtained via linkage with Korea National Health Insurance Service (NHIS) claims data.

Maternal depression as assessed using the PHQ-9 (Patient Health Questionnaire-9) when the child is 42 months old. The PHQ-9 (Patient Health Questionnaire-9) was developed by Kroenke, K. et al. (2001) as a tool measuring the depression level of adults and composed of 9 items. The minimum score is 0 and the maximum score is 27, and higher score means a worse outcome.

Maternal depression as assessed using the PHQ-9 (Patient Health Questionnaire-9) when the child is 54 months old. The PHQ-9 (Patient Health Questionnaire-9) was developed by Kroenke, K. et al. (2001) as a tool measuring the depression level of adults and composed of 9 items. The minimum score is 0 and the maximum score is 27, and higher score means a worse outcome.

Maternal depression as assessed using the PHQ-9 (Patient Health Questionnaire-9) when the child is 66 months old. The PHQ-9 (Patient Health Questionnaire-9) was developed by Kroenke, K. et al. (2001) as a tool measuring the depression level of adults and composed of 9 items. The minimum score is 0 and the maximum score is 27, and higher score means a worse outcome.

Maternal parenting behavior as assessed using a 17-item questionnaire measuring two dimensions: warm/responsive parenting and controlling parenting when the child is 42 months old. The warm/responsive dimension includes 9 items adapted by the Korea Institute of Child Care and Education from the Parental Style Questionnaire (Bornstein et al., 1996). The controlling dimension includes 8 items adapted by the Korea Institute of Child Care and Education based on Cho et al. (1999). Responses are rated on a 5-point Likert scale, with higher scores indicating greater endorsement of each parenting style.

Maternal parenting behavior as assessed using a 17-item questionnaire measuring two dimensions: warm/responsive parenting and controlling parenting when the child is 54 months old. The warm/responsive dimension includes 9 items adapted by the Korea Institute of Child Care and Education from the Parental Style Questionnaire (Bornstein et al., 1996). The controlling dimension includes 8 items adapted by the Korea Institute of Child Care and Education based on Cho et al. (1999). Responses are rated on a 5-point Likert scale, with higher scores indicating greater endorsement of each parenting style.

Maternal parenting behavior as assessed using the 32-item Parenting Style and Dimensions Questionnaire (32-PSDQ), measuring authoritative, authoritarian, and permissive parenting styles, adapted from Robinson et al. (2001) and used in the Korean Early Childhood Education and Care Panel Study.

Cognitive-stimulating home environment as assessed using the Home Environment Activities and Cognitive Stimulation (HEQ) questionnaire adapted from the Early Childhood Longitudinal Study Kindergarten Cohort (ECLS-K) when the child is 42 months old. The Korean version was translated by the Korea Institute of Child Care and Education. The instrument consists of 10 items measuring frequency of cognitive stimulation activities between parents and children over the past week, rated on a 4-point scale.

Cognitive-stimulating home environment as assessed using the Home Environment Activities and Cognitive Stimulation (HEQ) questionnaire adapted from the Early Childhood Longitudinal Study Kindergarten Cohort (ECLS-K) when the child is 54 months old. The Korean version was translated by the Korea Institute of Child Care and Education. The instrument consists of 10 items measuring frequency of cognitive stimulation activities between parents and children over the past week, rated on a 4-point scale.

Cognitive-stimulating home environment as assessed using the Home Environment Activities and Cognitive Stimulation (HEQ) questionnaire adapted from the Early Childhood Longitudinal Study Kindergarten Cohort (ECLS-K) when the child is 66 months old. The Korean version was translated by the Korea Institute of Child Care and Education. The instrument consists of 10 items measuring frequency of cognitive stimulation activities between parents and children over the past week, rated on a 4-point scale.

Safety knowledge as measured by the number of questions the mother answered correctly about child accident prevention when the child is 6 months old. The questionnaire testing mothers' safety knowledge is composed of five items from the Korean National Health Insurance Service's Infant Health Examination Questionnaire.

Safety knowledge as measured by the number of questions the mother answered correctly about child accident prevention when the child is 12 months old. The questionnaire testing mothers' safety knowledge is composed of five items from the Korean National Health Insurance Service's Infant Health Examination Questionnaire.

Safety knowledge as measured by the number of questions the mother answered correctly about child accident prevention when the child is 24 months old. The questionnaire testing mothers' safety knowledge is composed of five items from the Korean National Health Insurance Service's Infant Health Examination Questionnaire.

Number of emergency department visits when the child is 6 weeks old.

Number of emergency department visits when the child is 6 months old.

Number of emergency department visits when the child is 12 months old.

Number of emergency department visits when the child is 24 months old.

Number of hospital admission when the child is 6 weeks old.

Number of hospital admission when the child is 6 months old.

Number of hospital admission when the child is 12 months old.

Number of hospital admission when the child is 24 months old.

Child development as assessed using Denver (Denver Developmental Screening Test) II when the child is 6 months old.

Child development as assessed using Denver (Denver Developmental Screening Test) II when the child is 12 months old.

Child development as assessed using Denver (Denver Developmental Screening Test) II when the child is 24 months old.

Premature birth as assessed by asking the mother whether the child was delivered before 37 weeks.

Height in centimeters measured by a physical examination of the child when the child is 6 months old.

Height in centimeters measured by a physical examination of the child when the child is 12 months old.

Height in centimeters measured by a physical examination of the child when the child is 24 months old.

Weight in kilograms measured by a physical examination of the child when the child is 6 months old.

Weight in kilograms measured by a physical examination of the child when the child is 12 months old.

Weight in kilograms measured by a physical examination of the child when the child is 24 months old.

Head circumference in centimeters measured by a physical examination of the child when the child is 6 months old.

Head circumference in centimeters measured by a physical examination of the child when the child is 12 months old.

Head circumference in centimeters measured by a physical examination of the child when the child is 24 months old.

Knowledge of SIDS (sudden infant death syndrome) prevention as measured by the number of questions the mother answered correctly about SIDS prevention when the child is 6 months old. The questionnaire testing the mother's knowledge of SIDS is composed of five items from the Korean National Health Insurance Service's Infant Health Examination Questionnaire.

Vaccination as assessed by the completion of recommended vaccinations (tuberculosis, hepatitis B, Haemophilus influenzae type b (Hib), DTaP, polio, Streptococcus pneumoniae) when the child is 6 months old.

Vaccination as assessed by the completion of recommended vaccinations (tuberculosis, hepatitis B, Haemophilus influenzae type b (Hib), DTaP, polio, Streptococcus pneumoniae) when the child is 12 months old.

Vaccination as assessed by the completion of recommended vaccinations (tuberculosis, hepatitis B, Haemophilus influenzae type b (Hib), DTaP, polio, Streptococcus pneumoniae) when the child is 24 months old.

National health check-ups assessed by asking whether the mother has visited a health center or pediatrician for an infant health checkup when the child is 6 months old.

National health check-ups assessed by asking whether the mother has visited a health center or pediatrician for an infant health checkup when the child is 12 months old.

National health check-ups assessed by asking whether the mother has visited a health center or pediatrician for an infant health checkup when the child is 24 months old.

Spousal participation in parenting as measured by a questionnaire composed of 4 items when the child is 6 months old. The questionnaire was developed by Hong (1995) and used in the Panel Study on Korean Children (PSKC). The minimum score is 4 and the maximum score is 20, and a higher score means a better outcome.

Spousal participation in parenting as measured by a questionnaire composed of 4 items when the child is 12 months old. The questionnaire was developed by Hong (1995) and used in the Panel Study on Korean Children (PSKC). The minimum score is 4 and the maximum score is 20, and a higher score means a better outcome.

Spousal participation in parenting as measured by a questionnaire composed of 4 items when the child is 24 months old. The questionnaire was developed by Hong (1995) and used in the Panel Study on Korean Children (PSKC). The minimum score is 4 and the maximum score is 20, and a higher score means a better outcome.

Parenting-related household expenses, which measure a household's expenditures for pregnancy, childbirth, and supplies needed to care for the child when the child is 6 months old.

Parenting-related household expenses, which measure a household's expenditures for pregnancy, childbirth, and supplies needed to care for the child when the child is 12 months old.

Parenting-related household expenses, which measure a household's expenditures for pregnancy, childbirth, and supplies needed to care for the child when the child is 24 months old.

Intention to have another child as assessed by a single question, "Do you have any intention to have more children in the future?". Responses to this question are categorized into three options: "Yes, I have the intention to have another child", "No, I don't have the intention to have another child", and "I don't know."

Experience of delivery in the past 2 years as assessed by using a single question: "Have you had the experience of subsequent childbirth (having another child after participating in the study) or are you currently pregnant?" Responses to this question are categorized into three options: "Yes, I have had subsequent childbirth experience," "Yes, I am currently pregnant," and "No, I don't have subsequent childbirth."

Depression as assessed using the EPDS (Edinburgh Postnatal Depression Scale) when the child is 6 months old. The EPDS (Edinburgh Postnatal Depression Scale) was developed by Cox et al. (1987) as a tool measuring postnatal depression. It is composed of 10 items. The minimum score is 0 and the maximum score is 30, and a higher score means a worse outcome.

Depression as assessed using the EPDS (Edinburgh Postnatal Depression Scale) when the child is 12 months old. The EPDS (Edinburgh Postnatal Depression Scale) was developed by Cox et al. (1987) as a tool measuring postnatal depression. It is composed of 10 items. The minimum score is 0 and the maximum score is 30, and a higher score means a worse outcome.

Depression as assessed using the EPDS (Edinburgh Postnatal Depression Scale) when the child is 24 months old. The EPDS (Edinburgh Postnatal Depression Scale) was developed by Cox et al. (1987) as a tool measuring postnatal depression. It is composed of 10 items. The minimum score is 0 and the maximum score is 30, and a higher score means a worse outcome.

Suicidal ideation as assessed using the 10th item of EPDS (Edinburgh Postnatal Depression Scale) when the child is 6 months old. The EPDS (Edinburgh Postnatal Depression Scale) was developed by Cox et al. (1987) as a tool measuring postnatal depression and the 10th item of EPDS asks respondents to indicate how often they have experienced thoughts of self harm using a 4-point frequency scale.

Suicidal ideation as assessed using the 10th item of EPDS (Edinburgh Postnatal Depression Scale) when the child is 12 months old. The EPDS (Edinburgh Postnatal Depression Scale) was developed by Cox et al. (1987) as a tool measuring postnatal depression and the 10th item of EPDS asks respondents to indicate how often they have experienced thoughts of self harm using a 4-point frequency scale.

Suicidal ideation as assessed using the 10th item of EPDS (Edinburgh Postnatal Depression Scale) when the child is 24 months old. The EPDS (Edinburgh Postnatal Depression Scale) was developed by Cox et al. (1987) as a tool measuring postnatal depression and the 10th item of EPDS asks respondents to indicate how often they have experienced thoughts of self harm using a 4-point frequency scale.

Depression as assessed using the PHQ-9 (Patient Health Questionnaire-9) when the child is 6 months old. The PHQ-9 (Patient Health Questionnaire-9) was developed by Kroenke, K. et al. (2001) as a tool measuring the depression level of adults and composed of 9 items. The minimum score is 0 and the maximum score is 27, and higher score means a worse outcome.

Depression as assessed using the PHQ-9 (Patient Health Questionnaire-9) when the child is 12 months old. The PHQ-9 (Patient Health Questionnaire-9) was developed by Kroenke, K. et al. (2001) as a tool measuring the depression level of adults and composed of 9 items. The minimum score is 0 and the maximum score is 27, and higher score means a worse outcome.

Depression as assessed using the PHQ-9 (Patient Health Questionnaire-9) when the child is 24 months old. The PHQ-9 (Patient Health Questionnaire-9) was developed by Kroenke, K. et al. (2001) as a tool measuring the depression level of adults and composed of 9 items. The minimum score is 0 and the maximum score is 27, and higher score means a worse outcome.

Maternal depression as assessed using the Whooley & Arroll questions when the child is 6 weeks old. To screen depression in outpatient settings, a simple tool called " two screening questions" was developed. Arroll B. et al. (2005) enhanced the sensitivity and specificity of the tool by adding a "help-seeking question". If the response to at least one of the Screening 2-Item questions is affirmative or if the response to the help-seeking question is affirmative, further evaluation is necessary.

Maternal depression as assessed using the Whooley & Arroll questions when the child is 18 months old. To screen depression in outpatient settings, a simple tool called " two screening questions" was developed. Arroll B. et al. (2005) enhanced the sensitivity and specificity of the tool by adding a "help-seeking question". If the response to at least one of the Screening 2-Item questions is affirmative or if the response to the help-seeking question is affirmative, further evaluation is necessary.

Anxiety level as assessed using the GAD-2 (Generalized Anxiety Disorder 2-item) when the child is 6 months old. The GAD-2 (Generalized Anxiety Disorder 2-item) is a 2-item questionnaire that measures core anxiety symptoms. The minimum score is 0 and the maximum score is 6, and higher score means a worse outcome.

Anxiety level as assessed using the GAD-2 (Generalized Anxiety Disorder 2-item) when the child is 12 months old. The GAD-2 (Generalized Anxiety Disorder 2-item) is a 2-item questionnaire that measures core anxiety symptoms. The minimum score is 0 and the maximum score is 6, and higher score means a worse outcome.

Anxiety level as assessed using the GAD-2 (Generalized Anxiety Disorder 2-item) when the child is 24 months old. The GAD-2 (Generalized Anxiety Disorder 2-item) is a 2-item questionnaire that measures core anxiety symptoms. The minimum score is 0 and the maximum score is 6, and higher score means a worse outcome.

Maternal tobacco use assessed by current tobacco use status when the child is 6 months old. Maternal tobacco use is assessed by questioning the participants about their current tobacco use behavior during the month before the study.

Maternal tobacco use assessed by current tobacco use status when the child is 12 months old. Maternal tobacco use is assessed by questioning the participants about their current tobacco use behavior during the month before the study.

Maternal tobacco use assessed by current tobacco use status when the child is 24 months old. Maternal tobacco use is assessed by questioning the participants about their current tobacco use behavior during the month before the study.

Maternal alcohol consumption when the child is 6 months old. Maternal alcohol consumption is assessed by questioning the participants about their drinking behavior during the month before the study.

Maternal alcohol consumption when the child is 12 months old. Maternal alcohol consumption is assessed by questioning the participants about their drinking behavior during the month before the study.

Maternal alcohol consumption when the child is 24 months old. Maternal alcohol consumption is assessed by questioning the participants about their drinking behavior during the month before the study.

Delivery type as assessed by asking a mother to choose her delivery type between "normal delivery," "planned C-section," and "unplanned emergency C-section" when the child is 6 weeks old.

Maternal parenting stress as assessed using the Being a Mother Scale (BaM-13) when the child is 6 months old. The Being a Mother Scale (BaM-13) was developed by Matthey (2011) for assessing mothers' level of distress. It is composed of 13 items. The minimum score is 0 and the maximum score is 39, and a higher score means a high level of distress.

Maternal parenting stress as assessed using the Being a Mother Scale (BaM-13) when the child is 12 months old. The Being a Mother Scale (BaM-13) was developed by Matthey (2011) for assessing mothers' level of distress. It is composed of 13 items. The minimum score is 0 and the maximum score is 39, and a higher score means a high level of distress.

Maternal parenting stress as assessed using the Being a Mother Scale (BaM-13) when the child is 24 months old. The Being a Mother Scale (BaM-13) was developed by Matthey (2011) for assessing mothers' level of distress. It is composed of 13 items. The minimum score is 0 and the maximum score is 39, and a higher score means a high level of distress.

Intimate partner violence as assessed using the HITS (Hurt, Insult, Threaten, and Scream) tool when the child is 6 months old. The HITS (Hurt, Insult, Threaten, and Scream) tool was developed by Sherin et al. (1998) for assessing the level of domestic violence. It is composed of 4 items. The minimum score is 4 and the maximum score is 20, and higher score means a high level of domestic violence.

Intimate partner violence as assessed using the HITS (Hurt, Insult, Threaten, and Scream) tool when the child is 12 months old. The HITS (Hurt, Insult, Threaten, and Scream) tool was developed by Sherin et al. (1998) for assessing the level of domestic violence. It is composed of 4 items. The minimum score is 4 and the maximum score is 20, and higher score means a high level of domestic violence.

Intimate partner violence as assessed using the HITS (Hurt, Insult, Threaten, and Scream) tool when the child is 24 months old. The HITS (Hurt, Insult, Threaten, and Scream) tool was developed by Sherin et al. (1998) for assessing the level of domestic violence. It is composed of 4 items. The minimum score is 4 and the maximum score is 20, and higher score means a high level of domestic violence.

Maternal body weight when the child is 6 weeks old.

Maternal body weight when the child is 6 months old.

Maternal body weight when the child is 12 months old.

Maternal body weight when the child is 24 months old.

Social support as measured by a questionnaire developed by the Korea Institute of Child Care and Education when the child is 6 months old. The questionnaire measuring social support developed and used by Korea Institute of Child Care and Education is composed of 12 items. The minimum score is 12 and the maximum score is 60, and a higher score means a better outcome.

Social support as measured by a questionnaire developed by the Korea Institute of Child Care and Education when the child is 12 months old. The questionnaire measuring social support developed and used by Korea Institute of Child Care and Education is composed of 12 items. The minimum score is 12 and the maximum score is 60, and a higher score means a better outcome.

Social support as measured by a questionnaire developed by the Korea Institute of Child Care and Education when the child is 24 months old. The questionnaire measuring social support developed and used by Korea Institute of Child Care and Education is composed of 12 items. The minimum score is 12 and the maximum score is 60, and a higher score means a better outcome.

Food insecurity assessed by asking about the family's level of limited access to adequate food over the past year when the child is 12 months.

Food insecurity assessed by asking about the family's level of limited access to adequate food over the past year when the child is 24 months.

Spousal intimacy as measured using the Revised-Kansas Marital Satisfaction Scale modified by the Korea Institute of Child Care and Education when the child is 6 months old. The Revised-Kansas Marital Satisfaction Scale modified by the Korea Institute of Child Care and Education is composed of 4 items. The minimum score is 4 and the maximum score is 20, and higher score means a better outcome.

Spousal intimacy as measured using the Revised-Kansas Marital Satisfaction Scale modified by the Korea Institute of Child Care and Education when the child is 12 months old. The Revised-Kansas Marital Satisfaction Scale modified by the Korea Institute of Child Care and Education is composed of 4 items. The minimum score is 4 and the maximum score is 20, and higher score means a better outcome.

Spousal intimacy as measured using the Revised-Kansas Marital Satisfaction Scale modified by the Korea Institute of Child Care and Education when the child is 24 months old. The Revised-Kansas Marital Satisfaction Scale modified by the Korea Institute of Child Care and Education is composed of 4 items. The minimum score is 4 and the maximum score is 20, and higher score means a better outcome.

Spousal tobacco use assessed by current tobacco use status when the child is 6 months old. Spouse tobacco use is assessed by questioning participants about their spouse's current tobacco use behavior during the month before the study.

Spousal tobacco use assessed by current tobacco use status when the child is 12 months old. Spouse tobacco use is assessed by questioning participants about their spouse's current tobacco use behavior during the month before the study.

Spousal tobacco use assessed by current tobacco use status when the child is 24 months old. Spouse tobacco use is assessed by questioning participants about their spouse's current tobacco use behavior during the month before the study.

Spousal alcohol consumption when the child is 6 months old. Spouse alcohol consumption is assessed by questioning participants about their spouse's drinking behavior during the month before the study.

Spousal alcohol consumption when the child is 12 months old. Spouse alcohol consumption is assessed by questioning participants about their spouse's drinking behavior during the month before the study.

Spousal alcohol consumption when the child is 24 months old. Spouse alcohol consumption is assessed by questioning participants about their spouse's drinking behavior during the month before the study.

Parent-child interaction as assessed by using the NCAST (Nursing Child Assessment Teaching Scale) when the child is 12 months old. The NCAST (Nursing Child Assessment Teaching Scale) was developed by Barnard (1989) for assessing parent-child interaction. It is composed of 73 items that measure sensitivity to cues, response to child's distress, cognitive growth fostering, clarity of cues, and responsiveness to caregiver. The minimum score is 0 and the maximum score is 105, and a higher score means a better outcome.

Parent-child interaction as assessed by using the NCAST (Nursing Child Assessment Teaching Scale) when the child is 24 months old. The NCAST (Nursing Child Assessment Teaching Scale) was developed by Barnard (1989) for assessing parent-child interaction. It is composed of 73 items that measure sensitivity to cues, response to child's distress, cognitive growth fostering, clarity of cues, and responsiveness to caregiver. The minimum score is 0 and the maximum score is 105, and a higher score means a better outcome.

Maternal safety knowledge assessed through age-appropriate questionnaire items from the Korean National Health Insurance Service's child Health Examination Questionnaire when the child is 42 months old.

Maternal safety knowledge assessed through age-appropriate questionnaire items from the Korean National Health Insurance Service's child Health Examination Questionnaire when the child is 54 months old.

Maternal safety knowledge assessed through age-appropriate questionnaire items from the Korean National Health Insurance Service's child Health Examination Questionnaire when the child is 66 months old.

Number of emergency department visits due to injuries as reported by mothers when the child is 42 months old.

Number of emergency department visits due to injuries as reported by mothers when the child is 54 months old.

Number of emergency department visits due to injuries as reported by mothers when the child is 66 months old.

Number of hospital admission as reported by mothers when the child is 66 months old.

Spousal participation in parenting as measured by a questionnaire composed of 4 items when the child is 66 months old. The questionnaire was developed by Hong (1995) and used in the Panel Study on Korean Children (PSKC). The minimum score is 4 and the maximum score is 20, and a higher score means a better outcome.

Parenting-related household expenses, which measure a household's expenditures for pregnancy, childbirth, and supplies needed to care for the child when the child is 66 months old.

Experience of subsequent childbirth after study participation as assessed by using a single question: "Have you had the experience of subsequent childbirth (having another child after participating in the study) or are you currently pregnant?" Responses to this question are categorized into three options: "Yes, I have had subsequent childbirth experience," "Yes, I am currently pregnant," and "No, I don't have subsequent childbirth."

Maternal anxiety level as assessed using the GAD-2 (Generalized Anxiety Disorder 2-item) scale when the child is 42 months old. The GAD-2 has a score range of 0-6, with higher scores indicating greater anxiety levels.

Maternal anxiety level as assessed using the GAD-2 (Generalized Anxiety Disorder 2-item) scale when the child is 54 months old. The GAD-2 has a score range of 0-6, with higher scores indicating greater anxiety levels.

Maternal anxiety level as assessed using the GAD-7 (Generalized Anxiety Disorder 7-item) scale when the child is 66 months old. The GAD-7 has a score range of 0-21, with higher scores indicating greater anxiety levels.

Maternal tobacco use assessed by current tobacco use status when the child is 66 months old. Maternal tobacco use is assessed by questioning the participants about their current tobacco use behavior during the month before the study.

Maternal alcohol consumption when the child is 66 months old. Maternal alcohol consumption is assessed by questioning the participants about their drinking behavior during the month before the study.

Maternal parenting stress as assessed using a questionnaire when the child is 66 months old. The questionnaire will measure maternal stress associated with parenting roles and childcare responsibilities, with higher scores indicating greater levels of parenting-related stress.

Intimate partner violence as assessed using the HITS (Hurt, Insult, Threaten, and Scream) tool when the child is 66 months old. The HITS (Hurt, Insult, Threaten, and Scream) tool was developed by Sherin et al. (1998) for assessing the level of domestic violence. It is composed of 4 items. The minimum score is 4 and the maximum score is 20, and higher score means a high level of domestic violence.

Social support as measured by a questionnaire developed by the Korea Institute of Child Care and Education when the child is 66 months old. The questionnaire is composed of 12 items. The minimum score is 12 and the maximum score is 60, and a higher score means a better outcome.

Food insecurity assessed by asking about the family's level of limited access to adequate food over the past year when the child is 66 months.

Spousal intimacy as measured using the Revised-Kansas Marital Satisfaction Scale modified by the Korea Institute of Child Care and Education when the child is 66 months old. The Scale is composed of 4 items. The minimum score is 4 and the maximum score is 20, and higher score means a better outcome.

Spousal tobacco use assessed by current tobacco use status when the child is 66 months old. Spouse tobacco use is assessed by questioning participants about their spouse's current tobacco use behavior during the month before the study.

Spousal alcohol consumption when the child is 66 months old. Spouse alcohol consumption is assessed by questioning participants about their spouse's drinking behavior during the month before the study.

Maternal employment status as assessed via self-report questionnaire when the child is 42 months old. Employment status will be categorized as employed (returned to pre-birth job, new employment, on leave), attending school, or unemployed/not in school using a simplified questionnaire adapted from the Korea Early Childhood Education and Care Panel Study.

Maternal employment status as assessed via self-report questionnaire when the child is 54 months old. Employment status will be categorized as employed (returned to pre-birth job, new employment, on leave), attending school, or unemployed/not in school using a simplified questionnaire adapted from the Korea Early Childhood Education and Care Panel Study.

Maternal employment status as assessed via self-report questionnaire when the child is 66 months old. A comprehensive questionnaire adapted from the Panel Study on Korean Children will be used to collect detailed information, including specific occupation type and workplace position.

Father's employment status will be assessed through maternal-report questionnaire adapted from the Panel Study on Korean Children when the child is 66 months old.

Self-reported average monthly household income over the past 12 months, measured in Korean Won.

Household classification under the National Basic Livelihood Security Act, categorized as basic livelihood security recipient, near-poor household, not applicable, or unknown.

Mother's marital status changes over time, categorized as single, married (first marriage), married (remarried), widowed, divorced, or separated when the child is 42 months old.

Mother's marital status changes over time, categorized as single, married (first marriage), married (remarried), widowed, divorced, or separated when the child is 54 months old.

Mother's marital status changes over time, categorized as single, married (first marriage), married (remarried), widowed, divorced, or separated when the child is 66 months old.

Self-reported enrollment status and type of educational facility currently attended by the child when the child is 42 months old.

Self-reported enrollment status and type of educational facility currently attended by the child when the child is 54 months old.

Self-reported enrollment status and type of educational facility currently attended by the child when the child is 66 months old.

Parental efficacy as assessed using a modified version of the Parenting Sense of Competence Scale originally developed by Gibaud-Wallston & Wandersman (1978) when the child is 42 months old. The instrument consists of 16 items rated on a 5-point scale.

Parental efficacy as assessed using a modified version of the Parenting Sense of Competence Scale originally developed by Gibaud-Wallston & Wandersman (1978) when the child is 54 months old. The instrument consists of 16 items rated on a 5-point scale.

Parental efficacy as assessed using a modified version of the Parenting Sense of Competence Scale originally developed by Gibaud-Wallston & Wandersman (1978) when the child is 66 months old. The instrument consists of 16 items rated on a 5-point scale.

Self-efficacy as assessed using the Self-Efficacy Scale originally developed by Pearlin et al. (1981). The Korean version was adapted by the Korea Institute of Child Care and Education and consists of 4 items rated on a 5-point Likert scale.

Number of outpatient visits and number of hospital admissions obtained through linkage with National Health Insurance Service data.

Participation in national health screening programs obtained through linkage with National Health Insurance Service data when the child is 66 months old.

Child lifestyle habits as assessed using selected items appropriate for 66-month-old children. The original tool was developed by Allen & Martoz (2003, 2007) and adapted and validated by the Panel Study on Korean Children (PSKC) research team. The assessment includes: (1) Daily sleep duration measured in hours, (2) Meal time regularity rated on a 5-point scale, (3) Weekly breakfast frequency at home, and (4) Media use frequency and age of first use for digital devices rated on a 5-point scale.

Child problem behavior as assessed using 10 items translated from the problem behavior section of the Korean version of Social Skills Rating System for preschool level (K-SSRS).

Child's social-emotional development as assessed using the social skills section of the Korean version of Social Skills Rating System for preschool level (K-SSRS). The instrument consists of 32 items originally used in the Panel Study on Korean Children (PSKC).

BMI calculated from height and weight measurements (kg/m²) obtained through physical examination.

Dental caries screening using the "lift the lip" screening method to assess tooth decay.

Mother's perception of her child's overall health status rated on a 5-point scale when the child is 42 months old.

Mother's perception of her child's overall health status rated on a 5-point scale when the child is 54 months old.

Mother's perception of her child's overall health status rated on a 5-point scale when the child is 66 months old.

Mother's perception of her own health status rated on a 5-point scale when the child is 42 months old.

Mother's perception of her own health status rated on a 5-point scale when the child is 54 months old.

Mother's perception of her own health status rated on a 5-point scale when the child is 66 months old.

Vaccination completion information obtained through linkage with Korea Disease Control and Prevention Agency vaccination data.

Community service linkage as measured by the number of community services a mother has received during the last year.

Mother's overall quality of life assessed through self-report questionnaire.