Maternal and paternal age at delivery, birth order, and risk of childhood onset type 1 diabetes: population based cohort study

ObjectiveTo estimate the associations of maternal and paternal age at delivery and of birth order with the risk of childhood onset type 1 diabetes.DesignCohort study by record linkage of the medical birth registry and the national childhood diabetes registry in Norway.SettingNorway.SubjectsAll live births in Norway between 1974 and 1998 (1.4 million people) were followed for a maximum of 15 years, contributing 8.2 million person years of observation during 1989-98. 1824 cases of type 1 diabetes diagnosed between 1989 and 1998 were identified.ResultsThere was no association between maternal age at delivery and type 1 diabetes among firstborn children, but among fourthborn children there was a 43.2% increase in incidence of diabetes for each five year increase in maternal age (95% confidence interval 6.4% to 92.6%). Each increase in birth order was associated with a 17.9% reduction in incidence (3.2% to 30.4%) when maternal age was 20-24 years, but the association was weaker when maternal age was 30 years or more. Paternal age was not associated with type 1 diabetes after maternal age was adjusted for.ConclusionsIntrauterine factors and early life environment may influence the risk of type 1 diabetes. The relation of maternal age and birth order to risk of type 1 diabetes is complex.

What is already known on this topic

Maternal age at birth is positively associated with risk of childhood onset type 1 diabetesStudies of the effect of birth order on risk of type 1 diabetes have given inconsistent results

What does this study add?

In a national cohort, risk of diabetes in firstborn children was not associated with maternal ageIncreasing maternal age was a risk factor in children born second or laterThe strength of the association increased with increasing birth order     

Risk Factors for Soil-Transmitted Helminth Infections during the First 3 Years of Life in the Tropics; Findings from a Birth Cohort

Background

Soil-transmitted helminths (STH) infect more than 2 billion humans worldwide, causing significant morbidity in children. There are few data on the epidemiology and risk factors for infection in pre-school children. To investigate risk factors for infection in early childhood, we analysed data prospectively collected in the ECUAVIDA birth cohort in Ecuador.

Methods and Findings

Children were recruited at birth and followed up to 3 years of age with periodic collection of stool samples that were examined microscopically for STH parasites. Data on social, demographic, and environmental risk factors were collected from the mother at time of enrolment. Associations between exposures and detection of STH infections were analysed by multivariable logistic regression. Data were analysed from 1,697 children for whom a stool sample was obtained at 3 years. 42.3% had at least one STH infection in the first 3 years of life and the most common infections were caused by A. lumbricoides (33.2% of children) and T. trichiura (21.2%). Hookworm infection was detected in 0.9% of children. Risk of STH infection was associated with factors indicative of poverty in our study population such as Afro-Ecuadorian ethnicity and low maternal educational level. Maternal STH infections during pregnancy were strong risk factors for any childhood STH infection, infections with either A. lumbricoides or T. trichiura, and early age of first STH infection. Children of mothers with moderate to high infections intensities with A. lumbricoides were most at risk.

Conclusions

Our data show high rates of infection with STH parasites during the first 3 years of life in an Ecuadorian birth cohort, an observation that was strongly associated with maternal STH infections during pregnancy. The targeted treatment of women of childbearing age, in particular before pregnancy, with anthelmintic drugs could offer a novel approach to the prevention of STH infections in pre-school children.     

Isonymic relationships in ethno-social categories (Argentinian colonial period) including illegitimate reproduction

Surnames provide a useful method to study the structure of human populations for which biological data are not available. The isonymic method has had multiple applications, but difficulties emerge when dealing with groups where extramarital reproduction is common and the sample size is small, and even more so when only paternal surnames are taken into account.Therefore, it could be of interest to retain female surnames, including those of unmarried mothers. This study was carried out using all birth records froman Argentinian population in the colonial period, which was characterized by the presence of different ethno-social groups (Spanish, Indian and 'Mestizo'or mixed Spanish-Indian) and various reproductive patterns regarding legitimacy. Coefficient of relationship by isonymy (Ri) kinship matrices between geographical populations were obtained, and the results derived from sets of surnames (paternal, maternal of legitimate and illegitimate children,and all surnames in the registers) compared. The results show similar surname distribution regardless of the set of surnames and group considered.Kinship Ri matrices using paternal surnames, maternal surnames of legitimate children, maternal surnames of illegitimate children, and the set of whole surnames showed the same relationships among populations, indicating a similar pattern for Spanish, Indian and Mixed ethno-social groups. Mantel test correlation between all pairs of matrices was significant in all different ethno-social groups. The results suggest that in populations with high illegitimacy, such as that studied here, it is possible to include maternal surnames, even corresponding to single mothers, in order to consider total reproduction and therefore maximize sample size.     

Associations of Maternal Diabetes During Pregnancy with Overweight in Offspring: Results from the Prospective TEDDY Study

Objective: This study aimed to determine the relationship between different forms of, and potential pathways between, maternal diabetes and childhood obesity at different ages. Methods: Prospective cohort data from The Environmental Determinants of Diabetes in the Young (TEDDY) study, which was composed of 5,324 children examined from 0.25 to 6 years of age, were analyzed. Cross‐sectional and longitudinal analyses taking into account potential confounders and effect modifiers such as maternal prepregnancy BMI and birth weight z scores were performed. Results: Offspring of mothers with gestational diabetes mellitus (GDM) or type 1 diabetes mellitus (T1DM) showed a higher BMI standard deviation score and increased risk for overweight and obesity at 5.5 years of age than offspring of mothers without diabetes. While these associations could be substantially explained by maternal prepregnancy BMI in offspring of mothers with GDM, significant associations disappeared after adjustment for birth weight z scores in offspring of T1DM mothers. Furthermore, overweight risk became stronger with increasing age in offspring of mothers with diabetes compared with offspring of mothers without diabetes. Conclusions: Maternal diabetes is associated with increased risk of offspring overweight, and the association appears to get stronger as children grow older. Indeed, intrauterine exposure to maternal T1DM may predispose children to later obesity through increased birth weight, while maternal BMI is more important in children exposed to GDM.     

Influence of variation in birth weight within normal range and within sibships on IQ at age 7 years: cohort study

ObjectiveTo examine the relation between birth weight and measured intelligence at age 7 years in children within the normal range of birth weight and in siblings.DesignCohort study of siblings of the same sex.Setting12 cities in the United States.Subjects3484 children of 1683 mothers in a birth cohort study during the years 1959 through 1966. The sample was restricted to children born at ⩾37 weeks gestation and with birth weights of 1500-3999 g.ResultsMean IQ increased monotonically with birth weight in both sexes across the range of birth weight in a linear regression analysis of one randomly selected sibling per family (n= 1683) with adjustment for maternal age, race, education, socioeconomic status, and birth order. Within same sex sibling pairs, differences in birth weight were directly associated with differences in IQ in boys (812 pairs, predicted IQ difference per 100 g change in birth weight =0.50, 95% confidence interval 0.28 to 0.71) but not girls (871 pairs, 0.10, −0.09 to 0.30). The effect in boys remained after differences in birth order, maternal smoking, and head circumference were adjusted for and in an analysis restricted to children with birth weight ⩾ 2500 g.ConclusionThe increase in childhood IQ with birth weight continues well into the normal birth weight range. For boys this relation holds within same sex sibships and therefore cannot be explained by confounding from family social environment.

What is already known on this topic

IQ at school age is linked to birth weight among low birthweight babiesSome evidence suggests the association might also apply to children of normal birth weight

What this study adds

IQ at age 7 years is linearly related to birth weight among children of normal birth weightThe relation was not due to confounding by maternal or socioeconomic factorsIQ is also associated with differences in birth weight between boy sibling pairs but not girls     

Positive Effect of Large Birth Intervals on Early Childhood Hemoglobin Levels in Africa Is Limited to Girls: Cross-Sectional DHS Study

Background

Short birth intervals are independently associated with increased risk of adverse maternal, perinatal, infant and child outcomes. Anemia in children, which is highly prevalent in Africa, is associated with an increased risk of morbidity and mortality. Birth spacing is advocated as a tool to reduce anemia in preschool African children, but the role of gender differences and contextual factors has been neglected. The present study aims to determine to what extent the length of preceding birth interval influences the hemoglobin levels of African preschool children in general, as well as for boys and girls separately, and which contextual factors thereby play a crucial role.

Methods and Findings

This cross-sectional study uses data from Demographic and Health Surveys (DHS) conducted between 2003 and 2011 in 20 African countries. All preschool children aged 6–59 months with a valid hemoglobin measurement and a preceding birth interval of 7–72 months as well as their corresponding multigravida mothers aged 21–49 years were included in the study. Hemoglobin levels of children and mothers were measured in g/l, while birth intervals were calculated as months difference between consecutive births. Multivariate analyses were done to examine the relationship between length of preceding birth interval and child hemoglobin levels, adjusted for factors at the individual, household, community, district, and country level. A positive linear relationship was observed between birth interval and the 49,260 included children’s hemoglobin level, whereby age and sex of the child, hemoglobin level of the mother, household wealth, mother’s education and urbanization of place of residence also showed positive associations. In the interaction models, the effect of a month increase in birth interval is associated with an average increase of 0.025 g/l in hemoglobin level (P = 0.001) in girls, while for boys the effect was not significant. In addition, for girls, the effect of length of preceding birth interval was highest in young mothers and mothers with higher hemoglobin levels, while for boys, the highest effect was noticed for those living in more highly educated regions. Finally, significantly higher hemoglobin levels of girls compared to boys were observed at birth but with increasing age, the sex difference in hemoglobin level gradually becomes smaller.

Conclusions

A longer birth interval has a modest positive effect on early childhood hemoglobin levels of girls, and this effect is strongest when their mothers are in their early twenties and have a high hemoglobin level. Remarkably, although the physiological iron requirement is higher for boys than girls, birth spacing has little influence on hemoglobin levels of preschool boys. We speculate that the preference for male offspring in large parts of Africa significantly influences nutritional patterns of African preschool boys and girls, and as such also determines the different effect of birth spacing. Finally, gender aspects should be considered in intervention programs that aim to improve anemia in African children.     

The effect of prenatal factors on crown dimensions

As shown in 870 white participants in the National Collaborative Perinatal Project (NCPP), maternal health status during pregnancy and birth size are systematically related to mesiodistal and buccolingual crown dimensions of I1, I2, dc, dm1, dm2 and M1. Maternal diabetes, maternal hypothyroidism and large size at birth are associated with larger maxillary and mandibular teeth in white children. Conversely, deciduous and permanent crown diameters are diminished in maternal hypertension, and in low birthweight and small birth-length conditions. These findings suggest that maternal and fetal (or gestational) determinants of both deciduous and permanent tooth crown dimensions may account for as much as half of crown-size variability with major implications to population comparisons and historical odontometric differences and trends.     

DNA methylation provides insight into intergenerational risk for preterm birth in African Americans

African Americans are at increased risk for spontaneous preterm birth (PTB). Though PTB is heritable, genetic studies have not identified variants that account for its intergenerational risk, prompting the hypothesis that epigenetic factors may also contribute. The objective of this study was to evaluate DNA methylation from maternal leukocytes to identify patterns specific to PTB and its intergenerational risk. DNA from peripheral leukocytes from African American women that delivered preterm (24–34 weeks; N = 16) or at term (39–41 weeks; N = 24) was assessed for DNA methylation using the HumanMethylation450 BeadChip. In maternal samples, 17,829 CpG sites associated with PTB, but no CpG site remained associated after correction for multiple comparisons. Examination of paired maternal-fetal samples identified 5,171 CpG sites in which methylation of maternal samples correlated with methylation of her respective fetus (FDR < 0.05). These correlated sites were enriched for association with PTB in maternal leukocytes. The majority of correlated CpG sites could be attributed to one or more genetic variants. They were also significantly more likely to be in genes involved in metabolic, cardiovascular, and immune pathways, suggesting a role for genetic and environmental contributions to PTB risk and chronic disease. The results of this study may provide insight into the factors underlying intergenerational risk for PTB and its consequences.     

The effect of the seasons of the year on malnutrition in North Korea

North Korea's economic isolation as a consequence of its recent nuclear testing could lead to another famine. In this context, the article investigates health determinants of the last famine. Birth season is a reliable proxy for nutritional and epidemiological circumstances in early life, which in turn can systematically influence later-life health outcomes such as stature. The aim of this study is to assess the effect of birth seasons on the development of heights. Height-for-age z-scores for up to 9934 pre-school children measured in 1997 during the North Korean food crisis in the decade of the 1990s and measured in 2002, are used for the analysis. Using these data, we have verified a number of earlier studies showing that cohorts born in winter are smaller. We have also found that cohorts born in autumn are taller. Additionally, when we control for sex, birthplace, and birth year, these calendar effects remain robust. Ignoring the humanitarian dilemma of any sort, it may be concluded that in totalitarian North Korea, Pyongyang can easily influence the biological welfare of its people by interfering with the birth calendar, in order to reduce the magnitude of a potentially upcoming famine.     

Socioeconomic Inequalities in Childhood Undernutrition in India: Analyzing Trends between 1992 and 2005

Background

India experienced a rapid economic boom between 1991 and 2007. However, this economic growth has not translated into improved nutritional status among young Indian children. Additionally, no study has assessed the trends in social disparities in childhood undernutrition in the Indian context. We examined the trends in social disparities in underweight and stunting among Indian children aged less than three years using nationally representative data.

Methods

We analyzed data from the three cross-sectional rounds of National Family Health Survey of India from 1992, 1998 and 2005. The social factors of interest were: household wealth, maternal education, caste, and urban residence. Using multilevel modeling to account for the nested structure and clustering of data, we fit multivariable logistic regression models to quantify the association between the social factors and the binary outcome variables. The final models additionally included age, gender, birth order of child, religion, and age of mother. We analyzed the trend by testing for interaction of the social factor and survey year in a dataset pooled from all three surveys.

Results

While the overall prevalence rates of undernutrition among Indian children less than three decreased over the 1992–2005 period, social disparities in undernutrition over these 14 years either widened or stayed the same. The absolute rates of undernutrition decreased for everyone regardless of their social status. The disparities by household wealth were greater than the disparities by maternal education. There were no disparities in undernutrition by caste, gender or rural residence.

Conclusions

There was a steady decrease in the rates of stunting in the 1992–2005 period, while the decline in underweight was greater between 1992 and 1998 than between 1998 and 2005. Social disparities in childhood undernutrition in India either widened or stayed the same during a time of major economic growth. While the advantages of economic growth might be reaching everyone, children from better-off households, with better educated mothers appear to have benefited to a greater extent than less privileged children. The high rates of undernutrition (even among the socially advantaged groups) and the persistent social disparities need to be addressed in an urgent and comprehensive manner.     

Soil-Transmitted Helminth Infections and Correlated Risk Factors in Preschool and School-Aged Children in Rural Southwest China

We conducted a survey of 1707 children in 141 impoverished rural areas of Guizhou and Sichuan Provinces in Southwest China. Kato-Katz smear testing of stool samples elucidated the prevalence of ascariasis, trichuriasis and hookworm infections in pre-school and school aged children. Demographic, hygiene, household and anthropometric data were collected to better understand risks for infection in this population. 21.2 percent of pre-school children and 22.9 percent of school aged children were infected with at least one of the three types of STH. In Guizhou, 33.9 percent of pre-school children were infected, as were 40.1 percent of school aged children. In Sichuan, these numbers were 9.7 percent and 6.6 percent, respectively. Number of siblings, maternal education, consumption of uncooked meat, consumption of unboiled water, and livestock ownership all correlated significantly with STH infection. Through decomposition analysis, we determined that these correlates made up 26.7 percent of the difference in STH infection between the two provinces. Multivariate analysis showed that STH infection is associated with significantly lower weight-for-age and height-for-age z-scores; moreover, older children infected with STHs lag further behind on the international growth scales than younger children.     

Parental age and the risk of childhood acute myeloid leukemia: results from the Childhood Leukemia International Consortium

BackgroundParental age has been associated with several childhood cancers, albeit the evidence is still inconsistent.AimTo examine the associations of parental age at birth with acute myeloid leukemia (AML) among children aged 0–14 years using individual-level data from the Childhood Leukemia International Consortium (CLIC) and non-CLIC studies.Material/methodsWe analyzed data of 3182 incident AML cases and 8377 controls from 17 studies [seven registry-based case-control (RCC) studies and ten questionnaire-based case-control (QCC) studies]. AML risk in association with parental age was calculated using multiple logistic regression, meta-analyses, and pooled-effect estimates. Models were stratified by age at diagnosis (infants <1 year-old vs. children 1–14 years-old) and by study design, using five-year parental age increments and controlling for sex, ethnicity, birthweight, prematurity, multiple gestation, birth order, maternal smoking and education, age at diagnosis (cases aged 1–14 years), and recruitment time period.ResultsAdjusted odds ratios (ORs) and 95% confidence intervals (CIs) derived from RCC, but not from the QCC, studies showed a higher AML risk for infants of mothers ≥40-year-old (OR = 6.87; 95% CI: 2.12–22.25). There were no associations observed between any other maternal or paternal age group and AML risk for children older than one year.ConclusionsAn increased risk of infant AML with advanced maternal age was found using data from RCC, but not from QCC studies; no parental age-AML associations were observed for older children.     

Predictors of accurate maternal perception of their preschool child's weight status among Hispanic WIC participants

Childhood obesity is a growing problem in the United States. Parental perception of their children's weight status is a key factor that needs to be considered when developing prevention programs for preschool children. Using a randomly selected sample of participants of Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) in Los Angeles County, we assessed accuracy of maternal perceptions of their children's weight status by comparing children's weight classification to the mothers' response to the question “Do you consider your child to be overweight, underweight or about right weight for (his) (her) height?” Additionally, we identified possible predictors of accurate maternal perception of their children's weight status by conducting a logistic regression model with child's gender, child's birth weight, maternal age, maternal BMI, maternal education, maternal acculturation level, and maternal language preference as potential predictors. Almost all mothers in the study classified their overweight or obese child as being about the right weight (93.6% and 77.5% of mothers, respectively). Maternal BMI and child's birth weight were the only predictors of maternal perception of their child's weight. Both were negatively associated with accuracy, with higher maternal BMI and higher infant birthweight associated with less accurate maternal perception of child weight. Parents need to be educated on the importance of childhood obesity and how to identify if their children are overweight or obese. If parents fail to recognize that their overweight child is overweight, then it is unlikely that they will recognize that interventions targeting obesity are relevant to their families.     

Paternal-age and birth-order effect on the human secondary sex ratio.

Because of conflicting results in previous analyses of possible maternal and paternal effects on the variation in sex ratio at birth, records of United States live births in 1975 were sorted by offspring sex, live birth order (based on maternal parity), parental races, and, unlike prior studies, ungrouped parental ages. Linear regression and logistic analysis showed significant effects of birth order and paternal age on sex ratio in the white race data (1.67 million births; 10,219 different combinations of independent variables). Contrary to previous reported results, the paternal-age effect cannot be ascribed wholly to the high correlation between paternal age and birth order as maternal age, even more highly correlated with birth order, does not account for a significant additional reduction in sex-ratio variation over that accounted for by birth order alone.     

Birth interval, mortality and growth of children in a rural area in Kenya

The impact of the length of birth intervals on mortality and growth of children from the perinatal period to 2 years in the Northern Division of Machakos District, Eastern Province, Kenya, were analyzed. There are 2 types of birth intervals: 1) the prospective birth interval--between the birth concerned (the 1st birth of the interval pair) and the subsequent birth; and 2) the retrospective birth interval--between the birth considered (the 2nd of the interval pair) and the preceeding birth. This study includes 3019 women who had at least 1 live birth between April, 1974 and April, 1981. They gave birth to 6778 children (including stillbirths). Births occurring in 1974 are excluded in the analysis because of considerable underregistration. 102 stillbirths and 213 deaths in the 1st 2 years are analyzed. They have been grouped into deaths during the perimatal period; the 1st year after the 1st week of life (infant period); and the 2nd year of life. The most convient method of analysis of the relation between retrospective birth interval and mortality is multivariate analysis, as the intermedicate biological and behavioral factors through which birth intervals can affect health are simultaneously influenced by other variables like maternal age and birth order; the log linear model is applied here. The probability of dying is the dependent variable. The impact of short prospective intervals are closely associated. Only infant and child deaths occurring after the conception of the next child are included. The size of cohorts in which these deaths occur can be calculated with a life table approach. The mortality probability between 5 and 12 months for children with short prospective intervals is .034. This is higher than the corresponding rate for all children in the area (P0.05). It is shown that children with short retrospective or prospective birth intervals do not run a greater risk of mortality or growth retardation than children with longer intervals, neither during the perinatal period nor during the 1st 2 years of life.     

Early influences on blood pressure: a study of children aged 5-7 years.

OBJECTIVE--To examine factors that influence blood pressure in children. DESIGN--Cross sectional study of children aged 5.0-7.0 years who had blood pressure measurements and for whom parental questionnaires were completed. SETTING--School based survey. SUBJECTS--3591 Children aged 5.0-7.5 years selected by stratified random sampling of primary schools in nine British towns (response rate 72%); 3591 were examined and their parental questionnaires were completed. Data were complete for birth rank in 3559, maternal age in 3542, maternal history of hypertension in 3524, and paternal history in 2633. RESULTS--Birth weight was inversely related to mean systolic blood pressure but only when standardised for current weight (weight standardised regression coefficient -1.83 mm Hg/kg (95% confidence interval -1.31 to -2.35). Mean diastolic pressure was similarly related to birth weight. Maternal age, birth rank, and a parental history of hypertension were all related to blood pressure. After standardisation for current weight a 10 year increase in maternal age was associated with a 1.0 mm Hg (0.4 to 1.6) rise in systolic pressure; first born children had systolic blood pressure on average 2.53 mm Hg (0.81 to 4.25) higher than those whose birth rank was greater than or equal to 4; and a maternal history of hypertension was associated with a systolic pressure on average 0.96 mm Hg (0.41 to 1.51) higher than in those with no such history. The effects described were largely independent of one another and of age and social class. The relation for birth rank was, however, closely related to that for family size. CONCLUSIONS--Influences acting in early life may be important determinants of blood pressure in the first decade. The relation between birth weight and blood pressure may reflect the rate of weight gain in infancy. The reasons for the relation with birth rank and maternal age are unknown; if confirmed they imply that delayed motherhood and smaller family size may be associated with higher blood pressure in offspring.     

Socio-economic status and z-score standardized height-for-age of U.S.-born children (ages 2–6)

This study explores socio-economic gradients in height (stature-for-age) among a nationally representative sample of 2–6 year old children in the United States. We use NHANES III (1988–1994) Youth data linked with a special Natality Data supplement which contains information from birth certificates among sampled NHANES III Youth who are <7 years of age. Our results indicate significant socio-economic gradients for both maternal education and family income, net of controls for confounders, including: birth weight, gestational age, family size, and parental heights. These results are in stark contrast to those from other developed countries that seem to indicate diminished or eliminated socio-economic disparities, net of known confounders. In the United States, it appears that socio-economic gradients have an effect on birth outcomes, and continue to have an additional direct and independent effect on height, even in early childhood.     

Size at birth, postnatal growth and risk of obesity

Epidemiological studies over the last 15 years have shown that size at birth, early postnatal catch-up growth and excess childhood weight gain are associated with an increased risk of adult cardiovascular disease and type 2 diabetes. At the same time, rising rates of obesity and overweight in children, even at pre-school ages, have shifted efforts towards the identification of very early factors that predict risk of subsequent obesity, which may allow early targeted interventions. Overall, higher birth weight is positively associated with subsequent greater body mass index in childhood and later life; however, the relationship is complex. Higher birth weight is associated with greater subsequent lean mass, rather than fat mass. In contrast, lower birth weight is associated with a subsequent higher ratio of fat mass to lean mass, and greater central fat and insulin resistance. This paradoxical effect of lower birth weight is at least partly explained by the observation that infants who have been growth restrained in utero tend to gain weight more rapidly, or 'catch up', during the early postnatal period, which leads to increased central fat deposition. There is still debate as to whether there are critical early periods for obesity: does excess weight gain during infancy, childhood or even very early neonatal life have a greater impact on long-term fat deposition and insulin resistance? Early identification of childhood obesity risk will be aided by identification of maternal and fetal genes that regulate fetal nutrition and growth, and postnatal genes that regulate appetite, energy expenditure and the partitioning of energy intake into fat or lean tissue growth.     

Scaling-Up Access to Family Planning May Improve Linear Growth and Child Development in Low and Middle Income Countries

Background

A large literature has indicated a robust association between birth spacing and child survival, but evidence on the association of birth timing with physical growth in low and middle income countries (LMICs) remains limited.

Methods and Results

Data from 153 cross-sectional Demographic and Health Surveys (DHS) across 61 LMICs conducted between 1990 and 2011 were combined to assess the association of birth timing with child stunting (height-for-age z-score <−2). A total of 623,789 children of birth order 1–5 contributed to the maternal age analysis, while the birth spacing dataset consisted of 584,226 children of birth order 2 and higher. Compared to 27–34 year old mothers, maternal age under 18 years was associated with a relative stunting risk of 1.35 (95% CI: 1.29–1.40) for firstborn children, whereas the relative risk was 1.24 (95% CI: 1.19–1.29) for mothers aged 18–19 years. The association of young maternal age with stunting was significantly greater for urban residents and those in the top 50% of household wealth. Birth intervals less than 12 months and 12–23 months had relative risks for stunting of 1.09 (95% CI: 1.06–1.12) and 1.06 (95% CI: 1.05–1.06) as compared to a 24–35 month inter-pregnancy interval, respectively. The strength of both teenage pregnancy and short birth interval associations showed substantial variation across WHO region. We estimate that 8.6% (6.9–10.3%) of stunted cases in the South Asian DHS sample would have been averted by jointly eliminating teen pregnancies and birth intervals less than 24 months, while only 3.6% (1.5–5.7%) of stunting cases would have prevented in the Middle East and North Africa sample.

Conclusions

Postponing the age of first birth and increasing inter-pregnancy intervals has the potential to significantly reduce the prevalence of stunting and improve child development in LMICs.