Birth Spacing and Risk of Autism and Other Neurodevelopmental Disabilities: A Systematic Review

Association between interpregnancy interval and risk of autism spectrum disorder: a systematic review and Bayesian network meta-analysis

Although the risk of autism spectrum disorder (ASD) has been reported to be associated with interpregnancy intervals (IPIs), their association remains debatable due to inconsistent findings in existing studies. Therefore, the present study aimed to explore their association. PubMed, Embase, Web of Science, and the Cochrane Library were systematically retrieved up to May 25, 2022. An updated search was performed on May 25, 2023, to encompass recent studies. The quality of the included studies was assessed using the Newcastle-Ottawa Scale (NOS). Our primary outcome measures were expressed as adjusted odds ratios (ORs). Given various control measures for IPI and diverse IPI thresholds in the included studies, a Bayesian network meta-analysis was performed. Eight studies were included, involving 24,865 children with ASD and 2,890,289 children without ASD. Compared to an IPI of 24 to 35 months, various IPIs were significantly associated with a higher risk of ASD (IPIs < 6 months: OR = 1.63, 95% CI 1.53-1.74, n = 5; IPIs of 6-11 months: OR = 1.50, 95% CI 1.42-1.59, n = 4; IPIs of 12-23 months: OR = 1.19, 95% CI 1.12-1.23, n = 10; IPIs of 36-59 months: OR = 0.96, 95% CI 0.94-0.99, n = 2; IPIs of 60-119 months: OR = 1.15, 95% CI 1.10-1.20, n = 4; IPIs > 120 months: OR = 1.57, 95% CI 1.43-1.72, n = 4). After adjusting confounding variables, our analysis delineated a U-shaped restricted cubic spline curve, underscoring that both substantially short (< 24 months) and excessively long IPIs (> 72 months) are significantly correlated with an increased risk of ASD.  Conclusion: Our analysis indicates that both shorter and longer IPIs might predispose children to a higher risk of ASD. Optimal childbearing health and neurodevelopmental outcomes appear to be associated with a moderate IPI, specifically between 36 and 60 months. What is Known: • An association between autism spectrum disorder (ASD) and interpregnancy intervals (IPIs) has been speculated in some reports. • This association remains debatable due to inconsistent findings in available studies. What is New: • Our study delineated a U-shaped restricted cubic spline curve, suggesting that both shorter and longer IPIs predispose children to a higher risk of ASD. • Optimal childbearing health and neurodevelopmental outcomes appear to be associated with a moderate IPI, specifically between 36 and 60 months.

Interpregnancy interval and adverse birth outcomes: a population-based cohort study of twins

BACKGROUND

To investigate associations between interpregnancy intervals (IPIs) and adverse birth outcomes in twin pregnancies.

METHODS

This retrospective cohort study of 9,867 twin pregnancies in Western Australia from 1980-2015. Relative Risks (RRs) were estimated for the interval prior to the pregnancy (IPI) as the exposure and after the pregnancy as a negative control exposure for preterm birth (< 37 weeks), early preterm birth (< 34 weeks), small for gestational age (SGA: < 10th percentile of birth weight by sex and gestational age) and low birth weight (LBW: birthweight < 2,500 g).

RESULTS

Relative to IPIs of 18-23 months, IPIs of < 6 months were associated with a higher risk of early preterm birth (aRR 1.41, 95% CI 1.08-1.83) and LBW for at least one twin (aRR 1.16, 95% CI 1.06-1.28). IPIs of 6-11 months were associated with a higher risk of SGA (aRR 1.24, 95% CI 1.01-1.54) and LBW for at least one twin (aRR 1.09, 95% CI 1.01-1.19). IPIs of 60-119 months and ≥ 120 months were associated with an increased risk of preterm birth (RR 1.12, 95% CI 1.03-1.22; and (aRR 1.25, 95% CI 1.10-1.41, respectively), and LBW for at least one twin (aRR 1.17, 95% CI 1.08-1.28; and aRR 1.20, 95% CI 1.05-1.36, respectively). IPIs of ≥ 120 months were also associated with an increased risk of early preterm birth (aRR 1.42, 95% CI 1.01-2.00). After negative control analysis, IPIs ≥ 120 months remained associated with early preterm birth and LBW.

CONCLUSION

Evidence for adverse associations with twin birth outcomes was strongest for long IPIs.

Interpregnancy interval and early infant neurodevelopment: the role of maternal-fetal glucose metabolism

BACKGROUND

Interpregnancy interval (IPI) is associated with a variety of adverse maternal and infant outcomes. However, reports of its associations with early infant neurodevelopment are limited and the mechanisms of this association have not been elucidated. Maternal-fetal glucose metabolism has been shown to be associated with infant neurodevelopmental. The objective of this study was to determine whether this metabolism plays a role in the relationship between IPI and neurodevelopment.

METHODS

This prospective birth cohort study included 2599 mother-infant pairs. The IPI was calculated by subtracting the gestational age of the current pregnancy from the interval at the end of the previous pregnancy. Neurodevelopmental outcomes at 12 months in infants were assessed by the Ages and Stages Questionnaire Edition 3 (ASQ-3). Maternal fasting venous blood was collected at 24-28 weeks and cord blood was collected at delivery. The association between IPI and neurodevelopment was determined by logistic regression. Mediation and sensitivity analyses were also conducted.

RESULTS

In our cohort, 14.0% had an IPI < 12 months. IPI < 12 months increased the failure of the communication domain, fine motor domain, and personal social domain of the ASQ (relative risks (RRs) with 95% confidence interval (CI): 1.73 [1.11,2.70]; 1.73 [1.10,2.72]; 1.51 [1.00,2.29]). Maternal homeostasis model assessment of insulin resistance (HOMA-IR) and cord blood C-peptide was significantly associated with failure in the communication domain [RRs with 95% CI: 1.15 (1.02, 1.31); 2.15 (1.26, 3.67)]. The proportion of the association between IPI and failure of the communication domain risk mediated by maternal HOMA-IR and cord blood C-peptide was 14.4%.

CONCLUSIONS

IPI < 12 months was associated with failing the communication domain in infants. Maternal-fetal glucose metabolism abnormality may partially explain the risk of neurodevelopmental delay caused by short IPI.

Association between inter-pregnancy interval and risk of adverse birth outcomes in subsequent pregnancy: A retrospective study from Jordan

BACKGROUND

Adverse birth outcomes, such as preterm birth and low birth weight (LBW), are leading causes of neonatal morbidity and mortality. In this study, we aimed to estimate the association between inter-pregnancy interval (IPI) and the risks of adverse birth outcomes in a subsequent pregnancy.

METHODS

We conducted a retrospective analysis involving 630 mothers who delivered a singleton live infant at a leading tertiary hospital in northern Jordan from March to August 2021. Outcome variables were preterm birth (<37 weeks of gestation) and LBW (<2.5 kg). Using multivariable logistic regression, the association between IPI and these two adverse birth outcomes was investigated.

RESULTS

The rates of preterm birth and LBW were 12.4% and 16.8%, respectively. Compared with an optimal IPI (24-36 months), a short IPI (<24 months) was positively associated with preterm birth (aOR: 4.09; 95% CI: 1.48-6.55) and LBW (aOR: 3.58; 95% CI: 1.57-5.15). Infants conceived after a long IPI (≥ 60 months) had increased odds of preterm birth (aOR: 3.78; 95% CI: 1.12-5.78) and LBW (aOR: 2.65; 95% CI: 1.67-4.03). Preterm delivery was also significantly associated with the mother's age (aOR: 1.10; 95% CI: 1.04-1.17), history of multiple cesarean births (aOR: 2.67; 95% CI: 1.14-4.29), prolonged rupture of membranes (aOR: 2.46; 95% CI: 1.10-5.52), and perinatal death (aOR: 3.42; 95% CI: 1.10-5.49). A mother's history of prior LBW (aOR: 4.39; 95% CI: 1.08-6.80), hypertensive disorders (aOR: 1.95; 95% CI: 1.03-3.89), and multiple cesarean births (aOR: 4.35; 95% CI: 2.10-6.99) was associated with LBW.

CONCLUSIONS

Both short and long IPIs were related to preterm delivery and LBW. Optimal birth spacing is recommended to improve birth outcomes and must be considered when designing effective family planning programs.

Interpregnancy interval and the risk of oppositional defiant disorder in offspring

The study aimed to investigate the association between interpregnancy interval (IPI) and parent-reported oppositional defiant disorder (ODD) in offspring at 7 and 10 years of age. We used data from the Avon Longitudinal Study of Parents and Children (ALSPAC), an ongoing population-based longitudinal study based in Bristol, United Kingdom (UK). Data included in the analysis consisted of more than 3200 mothers and their singleton children. The association between IPI and ODD was determined using a series of log-binomial regression analyses. We found that children of mothers with short IPI (<6 months) were 2.4 times as likely to have a diagnosis of ODD at 7 and 10 years compared to mothers with IPI of 18-23 months (RR = 2.45; 95%CI: 1.24-4.81 and RR = 2.40; 95% CI: 1.08-5.33), respectively. We found no evidence of associations between other IPI categories and risk of ODD in offspring in both age groups. Adjustment for a wide range of confounders, including maternal mental health, and comorbid ADHD did not alter the findings. This study suggests that the risk of ODD is higher among children born following short IPI (<6 months). Future large prospective studies are needed to elucidate the mechanisms explaining this association.

Investigating the direct and indirect associations between birth intervals and child growth and development: A cross-sectional analysis of 13 Demographic and Health Surveys

There is considerable literature on the associations of short birth intervals with adverse perinatal outcomes. However, less is known about the associations with child growth and development. In this study, we investigated the associations between birth intervals and child growth and development and examined child illness, child diet, and maternal stimulation as potential mechanisms. We pooled Demographic and Health Survey data on 8300 children aged 36–59 months from 13 countries (Benin, Burundi, Cambodia, Cameroon, Chad, Congo, Haiti, Honduras, Rwanda, Senegal, Timor-Leste, Togo, and Uganda). Longer birth interval was defined as a preceding birth interval ≥33 months. Child growth was assessed using height-for-age Z-score (HAZ). Child cognitive and socio-emotional development were measured using the Early Childhood Development Index. Child morbidity was defined as any illness in the past two weeks. Child diet was assessed using dietary diversity score and maternal stimulation by the number of stimulation activities. We used generalised linear models to estimate associations between longer birth intervals and child growth and development. Structural equation modelling was used to assess direct and indirect effects. In our sample, 44% of children had a preceding birth interval ≥33 months, 42% were stunted, 25% were cognitively off-track, and 33% socio-emotionally off-track. Longer birth intervals were associated with higher HAZ (mean difference 0.23 (95% CI 0.14, 0.32)) and socio-emotional development (relative risk (RR) 1.04 (95% CI 1.00, 1.09), but not cognitive development (RR 1.02 (95% CI 0.98, 1.06). We observed no significant indirect effects via child illness, child dietary diversity, or maternal stimulation. Although longer birth intervals were beneficial for child growth and socio-emotional development, we found no empirical support for the biological and behavioural mechanisms we explored. Additional research is needed to investigate alternative mechanisms to elucidate underlying processes and inform future interventions.

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Longer birth intervals were associated with improved child growth and development.

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Longer birth intervals were more beneficial for child outcomes in wealthier households.

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Child illness, diet, and stimulation were not empirically substantiated as mechanisms.

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Future research could explore additional biological and behavioural mechanisms.

Can women's 3E index impede short birth interval? evidence from Bangladesh Demographic and Health Survey, 2017-18

BACKGROUND

Women's empowerment, education, and economic status are jointly introduced as women's 3E. A number of studies found the significant association of these three variables with maternal health outcomes, but no studies, to the best of knowledge, have been found to justify the joint influence of women's 3E on the birth interval. As several studies have revealed that the short birth interval increases the risk of adverse maternal, perinatal, and infant outcomes and it is also responsible for increasing the country's population size, more research is needed on the birth interval. Therefore, the present study aimed to investigate the influence of women's 3E on the short birth interval after controlling the other selected covariates.

METHODS

Data from the Bangladesh Demographic and Health Survey (BDHS), 2017-18 have been used to serve the purpose of the study. To measure the birth interval, at least two live births for non-pregnant mothers and at least one live birth for currently pregnant mothers born in the 5 years before the survey were included in the study. The Chi-Square test was applied to know the unadjusted association of the selected covariates including women's 3E with the short birth interval. In order to find out the adjusted association of women's 3E with the short birth interval, sequential binary logistic regression models have been used.

RESULTS

The study found that about 23% of births in Bangladesh were born in a short birth interval. The likelihood of subsequent births of women decreases with an increase in the score of women's 3E before or after controlling the characteristics of women, child, and households. The results of the final model show that mothers with the coverage of 50% - 75%, 75% - 100%, and full coverage (100%) in 3E have a 23%, 41%, and 42% lower odds of having short birth interval compared to mothers with coverage of below 50% in 3E, respectively.

CONCLUSION AND RECOMMENDATION

Bangladesh still lags behind in meeting the minimum requirements for inter-birth intervals set by the World Health Organization. The study has shown that the 3E in women can contribute in prolonging the duration of subsequent births in Bangladesh. Policy-making interventions are needed to raise awareness among uneducated, under-empowered and economically poor reproductive women through family planning and fertility control programs so that the country can achieve the desired fertility rate.

The effects of birth spacing on early childhood development in high-income nations: A systematic review

OBJECTIVE

This study aimed to systematically review the literature on the associations between birth spacing and developmental outcomes in early childhood (3-10 years of age). Studies examining the associations between interpregnancy intervals and child development outcomes during and beyond the perinatal period have not been systematically reviewed.

METHODS

We searched Ovid/MEDLINE, Global Health, PsycINFO, EMBASE, CINAHL Plus, Educational Source, Research Starters, ERIC, Scopus, PubMed, Social Science Research Network database, and ProQuest's Social Sciences Databases for relevant articles published between 1 January 1989 and 25 June 2021. Studies published in English, conducted in populations residing in high-income countries with any measure of birth spacing, and child development outcomes among children aged <10 years were included. Two authors independently assessed the eligibility of studies and extracted data on the study design, setting and population, birth spacing, outcomes, and results.

RESULTS

The search yielded 1,556 records, of which seven studies met the inclusion criteria. Five of these seven studies used birth intervals as the exposure measure. Definitions of exposure differed between the studies. Three studies reported an association between short birth spacing and poorer child development outcomes, and two studies reported an association between long birth spacing and poorer child development outcomes.

CONCLUSION

Currently, limited evidence suggests that the adverse effects of sub-optimal birth spacing are observable beyond infancy.

Optimal interpregnancy interval in autism spectrum disorder: A multi-national study of a modifiable risk factor

It is biologically plausible that risk of autism spectrum disorder (ASD) is elevated by both short and long interpregnancy intervals (IPI). We conducted a retrospective cohort study of singleton, non-nulliparous live births, 1998-2007 in Denmark, Finland, and Sweden (N = 925,523 births). Optimal IPI was defined as the IPI at which minimum risk was observed. Generalized additive models were used to estimate relative risks (RR) of ASD and 95% Confidence Intervals (CI). Population impact fractions (PIF) for ASD were estimated under scenarios for shifts in the IPI distribution. We observed that the association between ASD (N = 9302) and IPI was U-shaped for all countries. ASD risk was lowest (optimal IPI) at 35 months for all countries combined, and at 30, 33, and 39 months in Denmark, Finland, and Sweden, respectively. Fully adjusted RRs at IPIs of 6, 12, and 60 months were 1.41 (95% CI: 1.08, 1.85), 1.26 (95% CI: 1.02, 1.56), and 1.24 (95% CI: 0.98, 1.58) compared to an IPI of 35 months. Under the most conservative scenario PIFs ranged from 5% (95% CI: 1%-8%) in Denmark to 9% (95% CI: 6%-12%) in Sweden. The minimum ASD risk followed IPIs of 30-39 months across three countries. These results reflect both direct IPI effects and other, closely related social and biological pathways. If our results reflect biologically causal effects, increasing optimal IPIs and reducing their indications, such as unintended pregnancy and delayed age at first pregnancy has the potential to prevent a salient proportion of ASD cases. LAY SUMMARY: Waiting 35 months to conceive again after giving birth resulted in the least risk of autism. Shorter and longer intervals resulted in risks that were up to 50% and 85% higher, respectively. About 5% to 9% of autism cases might be avoided by optimizing birth spacing.

Prevalence of short interpregnancy interval and its associated factors among pregnant women in Debre Berhan town, Ethiopia

Background

Short inter-pregnancy interval is an interval of <24 months between the dates of birth of the preceding child and the conception date of the current pregnancy. Despite its direct effects on the perinatal and maternal outcomes, there is a paucity of evidence on its prevalence and determinant factors, particularly in Ethiopia. Therefore, this study assessed the prevalence and associated factors of short inter-pregnancy interval among pregnant women in Debre Berhan town, Northern Ethiopia.

Methods

A community based cross-sectional study was conducted among a randomly selected 496 pregnant women in Debre Berhan town from February 9 to March 9, 2020. The data were collected by using an interviewer-administered questionnaire and analyzed using STATA (14.2) statistical software. To identify the predictors of short inter-pregnancy interval, multivariable binary logistic regression was fitted and findings are presented using adjusted odds ratio (AOR) with 95% confidence interval (CI).

Result

The overall prevalence of short inter-pregnancy interval (<24 months) among pregnant women was 205 (40.9%). Being over 30 years of age at first birth (AOR = 3.50; 95% CI: 2.12–6.01), non-use of modern contraceptive (AOR = 2.51; 95% CI: 1.23–3.71), duration of breastfeeding for less than 12 months (AOR = 2.62; 95% CI: 1.32–5.23), parity above four (AOR = 0.31; 95% CI: 0.05–0.81), and unintended pregnancy (AOR = 5.42; 95% CI: 3.34–9.22) were independently associated factors with short inter-pregnancy interval.

Conclusion

Despite the public health interventions being tried in the country, the prevalence of short inter-pregnancy interval in this study is high. Therefore, it implies that increasing contraceptive use and encouraging optimal breastfeeding might help in the efforts made to avert the problem.

Interpregnancy intervals and child development at age 5: a population data linkage study

OBJECTIVE

To investigate the associations between interpregnancy intervals (IPIs) and developmental vulnerability in children's first year of full-time school (age 5).

DESIGN

Retrospective cohort study using logistic regression. ORs were estimated for associations with IPIs with adjustment for child, parent and community sociodemographic variables.

SETTING

Western Australia (WA), 2002-2015.

PARTICIPANTS

34 574 WA born singletons with a 2009, 2012 or 2015 Australian Early Development Census (AEDC) record.

MAIN OUTCOME MEASURE

The AEDC measures child development across five domains; Physical Health and Wellbeing, Social Competence, Emotional Maturity, Language and Cognitive Skills (school-based) and Communication Skills and General Knowledge. Children with scores <10th percentile were classified as developmentally vulnerable on, one or more domains (DV1), or two or more domains (DV2).

RESULTS

22.8% and 11.5% of children were classified as DV1 and DV2, respectively. In the adjusted models (relative to the reference category, IPIs of 18-23 months), IPIs of <6 months were associated with an increased risk of children being classified as DV1 (adjusted OR (aOR) 1.17, 95% CI 1.08 to 1.34), DV2 (aOR 1.31, 95% CI 1.10 to 1.54) and an increased risk of developmental vulnerability for the domains of Physical Health and Wellbeing (aOR 1.25, 95% CI 1.06 to 1.48) and Emotional Maturity (aOR 1.36, 95% CI 1.12 to 1.66). All IPIs longer than the reference category were associated with and increased risk of children being classified as DV1 and DV2 (aOR >1.15). IPIs of 60-119 months and ≥120 months, were associated with an increased risk of developmental vulnerability on each of the five AEDC domains, with greater odds for each domain for the longer IPI category.

CONCLUSIONS

IPIs showed independent J-shaped relationships with developmental vulnerability, with short (<6 months) and longer (≥24 months) associated with increased risks of developmental vulnerability.

Prenatal and perinatal metabolic risk factors for autism: a review and integration of findings from population-based studies

PURPOSE OF REVIEW

Given the ongoing rise in prevalence of autism spectrum disorder (ASD) and the challenges in developing and administering interventions to significantly alleviate ASD symptoms, there is an urgent need to identify modifiable risk factors for ASD. The goal of this review is to systematically evaluate the current evidence for an association between conditions related to maternal metabolic syndrome and risk for ASD in offspring focusing on methodically rigorous studies.

RECENT FINDINGS

In recent years, multiple studies explored the association between various conditions related to maternal metabolic syndrome (obesity, hypertension, or diabetes prior to, or with onset during pregnancy) and ASD risk in the offspring.

SUMMARY

Examining large, sufficiently powered, population-based epidemiological studies that explored the association between maternal metabolic syndrome and ASD, we found consistent evidence for an association between maternal preeclampsia and risk for ASD. Other conditions that are part of maternal metabolic syndrome, including maternal obesity, gestational weight gain, diabetes and gestational diabetes, should be studied further with careful attention paid to potential synergistic effects between different metabolic conditions. These findings highlight the need for rigorous, large, population-based epidemiological studies of potentially modifiable ASD risk factors that could inform public health interventions.

Short birth spacing and its association with maternal educational status, contraceptive use, and duration of breastfeeding in Ethiopia. A systematic review and meta-analysis

Background

Closely spaced birth increases the risk of adverse maternal and child health outcomes. In Ethiopia, the prevalence of short birth spacing was highly variable across studies. Besides, contraceptive use, educational status, and duration of breastfeeding were frequently mentioned factors affecting short birth spacing. Therefore, this meta-analysis aimed to estimate the pooled prevalence of short birth spacing and its association with contraceptive use, educational status, and duration of breastfeeding among reproductive-age women in Ethiopia.

Methods

International databases: Google Scholar, PubMed, CINAHL, Cochrane library, HINARI, and Global Health were searched systematically to identify articles reporting the prevalence of short birth spacing and its association with contraceptive use, educational status, and duration of breastfeeding among reproductive-age women in Ethiopia. The data were analyzed by STATA/SE version-14 statistical software. The random-effect model was used to estimate the pooled prevalence of short birth spacing and the log odds ratio was used to determine the association. Moreover, egger’s test and I-squared statistics were used to assess publication bias and heterogeneity respectively.

Results

After reviewing 511 research articles, a total of nine articles with 5,682 study participants were included in this meta-analysis. The pooled prevalence of short birth spacing in Ethiopia was 46.9% [95% CI: (34.7, 59.1)]. Significant heterogeneity was observed between studies (I² = 98.4, p <0.001). Not using contraceptives [OR = 3.87, 95% CI: (2.29, 6.53)] and duration of breastfeeding < 24 months [OR = 16.9, 95%CI: (2.69, 106.47)] had a significant association with short birth spacing.

Conclusions

Although a minimum inter-pregnancy interval of two years was recommended by the World Health Organization (WHO), significant numbers of women still practiced short birth spacing in Ethiopia. Duration of breastfeeding and non-use of contraceptives were factors significantly associated with short birth spacing. So, efforts should be made to improve breastfeeding practice and contraceptive utilization among women in Ethiopia.

Factors influencing women's decisions about pregnancy spacing: Findings from a focus group discussion study

OBJECTIVES

Very short interpregnancy intervals are associated with negative health outcomes for mothers and children, and pregnancies with very short interpregnancy intervals are more likely to be unintended than pregnancies that are more widely spaced. The objective of this study was to improve understanding of women's motivations regarding pregnancy spacing.

METHODS

In 2017, we conducted 8 focus group discussions with 49 English- and Spanish-speaking postpartum women in central North Carolina. The groups explored participants' preferences for birth spacing and factors that influenced their decisions. We recorded, transcribed, and coded the discussions and analyzed these data for core themes.

RESULTS

Participants' ideas about when and whether to have more children were fluid-some had specific ideas during pregnancy or after delivery that changed over time; others had no definite plans. The primary reason for close birth spacing was to promote their children's having a closer relationship. Reasons for wider spacing included recovery from the previous pregnancy, challenges related to having 2 babies concurrently, and desire to wait for more favorable life circumstances. Participants did not mention health risks to children of short interpregnancy intervals and said that no health care providers discussed these risks with them. They had mixed perspectives about whether this information would influence their own child-spacing preferences but agreed that it should be shared with women to promote informed decision-making.

CONCLUSION

This study adds to limited research regarding the factors that women consider when determining pregnancy spacing. Better understanding of women's motivations can help inform counseling to help women achieve their desired pregnancy spacing.

Associated factors of pregnancy spacing among women of reproductive age Group in South of Iran: cross-sectional study

Background

Optimal pregnancy spacing is an important incidence in reproductive women’s health. Short or long pregnancy spacing leads to the greatest health, social and economic problems such as increase in maternal and infant mortality and morbidity, and adverse pregnancy outcomes. The aim of this study is to assess the mean of pregnancy spacing and associated factors of pregnancy spacing among women of reproductive age group with recurrent event analysis.

Methods

The fertility history of 1350 women aged 15–49 years was collected in this cross-sectional study. The women were selected through multistage random sampling method from a list of clinics in 2018. Some predictors were collected from their records and others were collected by face-to-face interview. The recurrent event survival analysis was used to explore the effect of predictors on pregnancy spacing. The R software program was used for analysis.

Results

There were nine predictors that had significant effect on pregnancy spacing. These predictors included the age of mother at marriage, mother’s BMI, contraception use, breast feeding duration of the previous child, the education level of husband, the sex preference of the mother, presence of abortion or stillbirth in the preceding pregnancies, income sufficiency, and mother’s awareness of optimum pregnancy interval. The most influential predictors; contraception use (HR = 2.34, 95%CI = 1.23 to 2.76, P < 0.001) and income sufficiency (HR = 2.046, 95%CI = 1.61 to 3.02, P = 0.018) lead to longer and son preference of mother (HR = 2.231, 95%CI = 1.24 to 2.81, P = 0.023) lead to shorter pregnancy spacing.

Conclusion

The up to date contraception tool should be at hand for couples to manage their pregnancy intervals. The unfavorable economic situation of a family leads to long pregnancy spacing. Despite the relative equality of the status of girls and boys in today’s societies, the desire to have a son child is still an important factor in shorter pregnancy spacing. The benefit of optimal pregnancy spacing should be more announced.

Inter-pregnancy interval and long-term neurological morbidity of the offspring

PURPOSE

The purpose of our study was to evaluate the effect of IPI on long-term neurological morbidity of the offspring.

METHODS

In this retrospective cohort study, 144,397 singleton infants born to multiparous mothers, between the years 1991 and 2014 in a tertiary medical center, were evaluated for different perinatal outcomes and were followed until 18 years of age for long-term neurological morbidity according to three IPI groups: Short IPI (< 6 months), long IPI (> 60 months) and intermediate IPI (6-60 months). We used a Kaplan-Meier survival curve to compare cumulative incidence of long-term neurological morbidity, and a Cox regression analysis to control for confounders such as gestational age, birth weight and maternal age.

RESULTS

Offspring born to mothers with long IPI had higher rates of neurological morbidity (3.62% among offspring born after long IPI vs. 3.18% and 3.19% among offspring born after short and intermediate IPI, respectively, p = 0.041). The cumulative incidence of long-term neurological morbidity was significantly higher in the long IPI group (Kaplan-Meier log-rank test p < 0.001). Being born after a long IPI was found to be an independent risk factor for long-term neurological morbidity of the offspring (adjusted hazard ratio 1.2; 95% confidence interval 1.1-1.4; p < 0.001).

CONCLUSION

Long IPI is independently associated with an increased risk of long-term neurological morbidity of the offspring.

A multilevel analysis of short birth interval and its determinants among reproductive age women in developing regions of Ethiopia

BACKGROUND

Short Birth Interval negatively affects the health of both mothers and children in developing nations, like, Ethiopia. However, studies conducted to date in Ethiopia upon short birth interval were inconclusive and they did not show the extent and determinants of short birth interval in developing (Afar, Somali, Gambella, and Benishangul-Gumuz) regions of the country. Thus, this study was intended to assess the short birth interval and its determinants in the four developing regions of the country.

METHODS

Data were retrieved from the Demographic and Health Survey program official database website (http://dhsprogram.com). A sample of 2683 women of childbearing age group (15-49) who had at least two alive consecutive children in the four developing regions of Ethiopia was included in this study. A multilevel multivariable logistic regression model was fitted to identify the independent predictors of short birth interval and Akaike's Information Criterion (AIC) was used during the model selection procedure.

RESULTS

In this study, the prevalence of short birth interval was 46% [95% CI; 43.7%, 47.9%]. The multilevel multivariable logistic regression model showed women living in rural area [AOR = 1.52, CI: 1.12, 2.05], women attended secondary education and above level [AOR = 0.27, CI: 0.05, 0.54], have no media exposure [AOR = 1.35, CI: 1.18, 1.56], female sex of the index child [AOR = 1.13, CI:1.07,1.20], breastfeeding duration [AOR = 0.79, CI: 0.77, 0.82], having six and more ideal number of children [AOR = 1.14, CI: 1.09, 1.20] and having preferred waiting time to birth two years and above [AOR = 0.86, CI: 0.78, 0.95] were the predictors of short birth interval.

CONCLUSIONS

The prevalence of short birth intervals in the developing regions of Ethiopia is still high. Therefore, the government of Ethiopia should work on the access of family planning and education in rural parts of the developing regions where more than 90% of the population in these regions is pastoral.

The effect of an educational video on long-acting reversible contraception (LARC) utilization at 6-8 weeks postpartum period: a randomized controlled trial

PURPOSE

Long-acting reversible contraception is highly effective in preventing unintended pregnancy and unsafe abortion. An educational video administered during early postpartum period might be an effective tool to improve postpartum LARC use. The objectives were to evaluate whether a postpartum educational video about LARC could increase postpartum LARC utilization at 6-8 weeks postpartum and to assess why postpartum women did not receive LARC.

METHODS

This randomized-controlled trial was conducted at the postpartum unit of a university Hospital between August 2016 and February 2017. Postpartum women who were aged > 20 years and willing to participate were recruited. Participants allocated to the study group watched the 7-min educational video on LARC methods while the control group did not. To assess LARC utilization, data were collected at 6-8 weeks postpartum using telephone calls and/or medical record review to determine postpartum contraception use and reasons for not using LARC.

RESULTS

Two-hundred and seventy participants were enrolled, and the video (135) and non-video (135) groups had similar baseline characteristics. In the video group, 57.8% (95% CI 49.0-66.2) reported using a LARC method, compared to 25.9% (95% CI 18.8-34.2) in the non-video group (p < 0.05). The reasons for not using LARC in both groups were inconvenience of access (42.0-43.8%) and uncertainty about methods (17.0-24.6%).

CONCLUSION

The educational video introduced at immediate postpartum period was efficacious in increasing the utilization of LARC at 6-8 weeks postpartum. Inconvenience of access was the most common reason cited for not using LARC.

CLINICAL TRIAL REGISTRATION NUMBER

Clinicaltrials.in.th TCTR20171225001 "retrospectively registered".

Interpregnancy interval and risk of perinatal death: a systematic review and meta-analysis

BACKGROUND

Interpregnancy interval (IPI) <6 months is a potentially modifiable risk factor for adverse perinatal health outcomes.

OBJECTIVE

This systematic review evaluated the international literature on the risk of perinatal death associated with IPI.

SEARCH STRATEGY

Two independent reviewers screened titles and abstracts identified in MEDLINE, EMBASE and Scopus from inception to 4 April 2019 (Prospero Registration #CRD42018092792).

SELECTION CRITERIA

Studies were included if they provided a description of IPI measurement and perinatal death, including stillbirth and neonatal death.

DATA COLLECTION AND ANALYSIS

A narrative review was performed for all included studies. Random effects meta-analysis was used to compare unadjusted odds of perinatal death associated with IPI <6 months and IPI ≥6 months. Analyses were performed by outcome of the preceding pregnancy and study location.

MAIN RESULTS

Of the 624 unique articles identified, 26 met the inclusion criteria. The pooled unadjusted odds ratio of perinatal death for IPI <6 months was 1.34 (95% CI 1.17-1.53) following a previous live birth, 0.85 (95% CI 0.73-0.99) following a previous miscarriage and 1.07 (95% CI 0.84-1.36) following a previous stillbirth compared with IPI ≥6 months. However, few high-income country studies reported an association after adjustment. Fewer studies evaluated the impact of long IPI on perinatal death and what evidence was available showed mixed results.

CONCLUSIONS

Results suggest a possible association between short IPI and risk of perinatal death following a live birth, particularly in low- to middle-income countries.

TWEETABLE ABSTRACT

Short IPI <6 months after a live birth was associated with greater risk of perinatal death than IPI ≥6 months.

Prenatal Depression and Risk of Short Interpregnancy Interval in a Predominantly Puerto Rican Population

Background: Short interpregnancy interval (IPI) is associated with risk of adverse pregnancy outcomes; however, few studies have evaluated the role of depression as a risk factor for short IPI. Puerto Rican women in the United States experience disparities in adverse birth outcomes and have the highest birth rates. Methods: We analyzed the association between prenatal depressive symptoms and IPI in Proyecto Buena Salud, a prospective cohort of predominantly Puerto Rican women in Western Massachusetts (2006-2011). Depression was measured using the Edinburgh Postnatal Depression Scale (EPDS) in early, mid, and late pregnancy. We calculated follow-up time as the difference between the date of delivery of the index pregnancy and the last menstrual period of the subsequent pregnancy using medical records and billing data. We defined short IPI as ≤18 months. Results: Of 1262 eligible women, 35% (n = 440) had at least probable minor depression (EPDS scores ≥13) and 25% (n = 315) had probable major depression (EPDS scores ≥15). Participants were followed for a median of 3.7 years (interquartile range = 1.4-6.0 years) and 240 (20.6%) participants experienced a short IPI. After adjusting for risk factors, women with probable minor depression (adjusted odds ratio [aOR] = 1.39, 95% confidence interval [CI] = 1.02-1.88) and probable major depression (aOR = 1.42, 95% CI = 1.02-1.97) during pregnancy had increased odds of short IPI. Conclusions: Prenatal depressive symptoms were common in this Puerto Rican population and were associated with a modest increase in odds of short IPI. Further examination of the pathways through which mental health may affect IPI in vulnerable populations is warranted.

Autism spectrum disorder

Autism spectrum disorder is a construct used to describe individuals with a specific combination of impairments in social communication and repetitive behaviours, highly restricted interests and/or sensory behaviours beginning early in life. The worldwide prevalence of autism is just under 1%, but estimates are higher in high-income countries. Although gross brain pathology is not characteristic of autism, subtle anatomical and functional differences have been observed in post-mortem, neuroimaging and electrophysiological studies. Initially, it was hoped that accurate measurement of behavioural phenotypes would lead to specific genetic subtypes, but genetic findings have mainly applied to heterogeneous groups that are not specific to autism. Psychosocial interventions in children can improve specific behaviours, such as joint attention, language and social engagement, that may affect further development and could reduce symptom severity. However, further research is necessary to identify the long-term needs of people with autism, and treatments and the mechanisms behind them that could result in improved independence and quality of life over time. Families are often the major source of support for people with autism throughout much of life and need to be considered, along with the perspectives of autistic individuals, in both research and practice.

Prenatal and Infancy Nurse Home Visiting Effects on Mothers: 18-Year Follow-up of a Randomized Trial

BACKGROUND

Prenatal and infancy home-visiting by nurses is promoted as a means of improving maternal life-course, but evidence of long-term effects is limited. We hypothesized that nurse-visitation would lead to long-term reductions in public-benefit costs, maternal substance abuse and depression, and that cost-savings would be greater for mothers with initially higher psychological resources.

METHODS

We conducted an 18-year follow-up of 618 out of 742 low-income, primarily African-American mothers with no previous live births enrolled in an randomized clinical trial of prenatal and infancy home visiting by nurses. We compared nurse-visited and control-group women for public-benefit costs, rates of substance abuse and depression, and examined possible mediators of intervention effects.

RESULTS

Nurse-visited women, compared with controls, incurred $17 310 less in public benefit costs (P = .03), an effect more pronounced for women with higher psychological resources ($28 847, P = .01). These savings compare with program costs of $12 578. There were no program effects on substance abuseor depression. Nurse-visited women were more likely to be married from child age 2 through 18 (19.2% vs 14.8%, P = .04), and those with higher psychological resources had 4.64 fewer cumulative years rearing subsequent children after the birth of the first child (P = .03). Pregnancy planning was a significant mediator of program effects on public benefit costs.

CONCLUSIONS

Through child age 18, the program reduced public-benefit costs, an effect more pronounced for mothers with higher psychological resources and mediated by subsequent pregnancy planning. There were no effects on maternal substance abuse and depression.

Le dépistage précoce du trouble du spectre de l’autisme chez les jeunes enfants

Le trouble du spectre de l’autisme (TSA) est un trouble neurodéveloppemental permanent qui se caractérise par des déficits de la communication sociale, un mode répétitif et restreint des comportements et des sensibilités ou des intérêts sensoriels inhabituels. Le TSA a des répercussions importantes sur la vie des enfants et de leur famille. À l’heure actuelle, sa prévalence estimative est de un cas sur 66 enfants et adolescents canadiens dans le groupe d’âge des cinq à 17 ans. Les pédiatres généraux, les médecins de famille et les autres professionnels de la santé rencontrent donc plus d’enfants ayant un TSA qu’auparavant dans leur pratique. Le diagnostic rapide de ce trouble et l’orientation des cas vers des interventions comportementales et éducationnelles intensives dès le plus jeune âge peuvent favoriser un meilleur pronostic clinique à long terme grâce à la neuroplasticité du cerveau à un plus jeune âge. Le présent docu-ment de principes contient des recommandations et des outils clairs, détaillés et fondés sur des données probantes pour aider les pédiatres communautaires et les autres dispensateurs de soins de première ligne à surveiller les tout premiers signes de TSA, ce qui constitue une étape importante vers un diagnostic précis et une évaluation détaillée des besoins pour planifier les interventions.

Early detection for autism spectrum disorder in young children

Autism spectrum disorder (ASD) is a life-long neurodevelopmental disorder, characterized by impairments in social communication, repetitive, restricted patterns of behaviour, and unusual sensory sensitivities or interests. ASD significantly impacts the lives of children and their families. Currently, the estimated prevalence of ASD is 1 in 66 Canadians aged 5 to 17 years. General paediatricians, family physicians, and other health care professionals are, therefore, seeing more children with ASD in their practices. The timely diagnosis of ASD, and referral for intensive behavioural and educational interventions at the earliest age possible, may lead to better long-term outcomes by capitalizing on the brain's neuroplasticity at younger ages. This statement provides clear, comprehensive, evidence-informed recommendations and tools to help community paediatricians and other primary care providers monitor for the earliest signs of ASD-an important step toward an accurate diagnosis and comprehensive needs assessment for intervention planning.

Obstetric Care Consensus No. 8: Interpregnancy Care

Interpregnancy care aims to maximize a woman's level of wellness not just in between pregnancies and during subsequent pregnancies, but also along her life course. Because the interpregnancy period is a continuum for overall health and wellness, all women of reproductive age who have been pregnant regardless of the outcome of their pregnancies (ie, miscarriage, abortion, preterm, full-term delivery), should receive interpregnancy care as a continuum from postpartum care. The initial components of interpregnancy care should include the components of postpartum care, such as reproductive life planning, screening for depression, vaccination, managing diabetes or hypertension if needed, education about future health, assisting the patient to develop a postpartum care team, and making plans for long-term medical care. In women with chronic medical conditions, interpregnancy care provides an opportunity to optimize health before a subsequent pregnancy. For women who will not have any future pregnancies, the period after pregnancy also affords an opportunity for secondary prevention and improvement of future health.

Short birth interval and associated factors among women of child bearing age in northern Ethiopia, 2016

Background

Short birth interval is known to have a negative effect on perinatal, neonatal and child health outcomes. In Ethiopia, 29% of births are short birth intervals at less than 24 months. Even though optimum birth spacing is considered as an essential factor for the health of women and their children, to the best of the authors’ knowledge studies conducted on short birth interval are insufficient to inform policy makers. Therefore, the aim of this study was to assess short birth interval and associated factors among women of child bearing age in Tigray, Ethiopia.

Methods

A community based cross-sectional study was conducted in Tselemti district among women of child bearing age from January 28 to February 28, 2016. Systematic sampling technique was used to select participants. Data were collected through face to face interviews and analyzed using SPSS version 20.0. Odds ratio along with 95% CI was computed to ascertain association between the outcome and predictor variables. A p-value of < 0.05 was considered as cut off point to assess significance of associations in the multivariable analysis.

Results

The overall prevalence of short birth interval among women of child bearing age was 187 (23.3%). Sub-optimum breastfeeding (AOR = 7.01; 95% CI: 3.64, 13.46), non-use of contraceptive (AOR = 2.44; 95% CI: 1.55, 3.82), being Muslim (AOR = 2.02; 95% CI: 1.20, 3.40) and not having desire to had the last child (AOR = 3.63; 95% CI: 2.23, 5.91) were factors associated with short birth interval.

Conclusion

Even though currently coverage of family planning use has increased, this study showed that short birth interval is still a concern for Ethiopian women due to factors such as: religion, suboptimum breastfeeding, unwanted pregnancy and non-use of contraceptives. Improving the accessibility and coverage of contraceptive use and involvement of religious leaders in family planning programs are essential strategies to be considered.

Electronic supplementary material

The online version of this article (10.1186/s12905-019-0776-4) contains supplementary material, which is available to authorized users.

Interpregnancy Care

Interpregnancy care aims to maximize a woman's level of wellness not just in between pregnancies and during subsequent pregnancies, but also along her life course. Because the interpregnancy period is a continuum for overall health and wellness, all women of reproductive age who have been pregnant regardless of the outcome of their pregnancies (ie, miscarriage, abortion, preterm, full-term delivery), should receive interpregnancy care as a continuum from postpartum care. The initial components of interpregnancy care should include the components of postpartum care, such as reproductive life planning, screening for depression, vaccination, managing diabetes or hypertension if needed, education about future health, assisting the patient to develop a postpartum care team, and making plans for long-term medical care. In women with chronic medical conditions, interpregnancy care provides an opportunity to optimize health before a subsequent pregnancy. For women who will not have any future pregnancies, the period after pregnancy also affords an opportunity for secondary prevention and improvement of future health.

Interpregnancy Intervals in a Contemporary Manitoba Cohort: Prevalence of So-Called Suboptimal Intervals and Associated Maternal Characteristics

OBJECTIVE

Short and long interpregnancy intervals (IPIs) have been associated with various adverse outcomes, and a 2016 American College of Obstetricians and Gynecologists' Committee Opinion recommends an optimal IPI of 18 months to 5 years. Descriptive data on the IPI in Canada are lacking. The objective of this study was to examine IPIs in a Manitoba cohort.

METHODS

The study analyzed a subset of records from a larger dataset used to examine the IPI and adverse perinatal outcomes. For that study, Manitoba's Hospital Abstracts data were searched to identify births from 1985 to 2014. Each two consecutive live births to the same mother formed a sibling pair. The IPI was calculated as the interval between the two siblings' births, minus the younger sibling's GA. Information on maternal characteristics was extracted from various datasets housed in the Manitoba Population Research Data Repository. The current analysis examined second and higher-order births between 2010 and 2014. The proportion of suboptimal IPIs was determined and IPIs were cross-tabulated with birth year and maternal subgroups.

RESULTS

More than half of pregnancies were conceived following a suboptimal interval. IPIs of less than 6 months - which have been associated with the highest risk of adverse outcomes - were more prevalent among certain subgroups. These included younger women as well as women who received inadequate prenatal care, smoked or drank alcohol during pregnancy, were low income, or did not graduate from high school.

CONCLUSION

Suboptimal IPIs were common in this Manitoba cohort. Stakeholders should consider whether greater efforts to promote appropriate birth spacing are warranted.

Adolescent fertility rates in a rural community in north-western Zambia: a retrospective study

Adolescent fertility rate is defined as the number of births per 1000 in women aged 15–19 years. These rates are highest in sub-Saharan Africa. National data from Zambia suggest the rate has declined from 179.6 in 1960 to 87.9 in 2015.

A retrospective study was performed at Chitokoloki Mission Hospital using the hospital delivery registers during January 2008 to December 2015. In this period, 945 (20.81%) births were to adolescent mothers. As morbidity is significant in this vulnerable group, strategies to reduce pregnancy rates among these young girls is much-needed.

Understanding environmental contributions to autism: Causal concepts and the state of science

The complexity of neurodevelopment, the rapidity of early neurogenesis, and over 100 years of research identifying environmental influences on neurodevelopment serve as backdrop to understanding factors that influence risk and severity of autism spectrum disorder (ASD). This Keynote Lecture, delivered at the May 2016 annual meeting of the International Society for Autism Research, describes concepts of causation, outlines the trajectory of research on nongenetic factors beginning in the 1960s, and briefly reviews the current state of this science. Causal concepts are introduced, including root causes; pitfalls in interpreting time trends as clues to etiologic factors; susceptible time windows for exposure; and implications of a multi-factorial model of ASD. An historical background presents early research into the origins of ASD. The epidemiologic literature from the last fifteen years is briefly but critically reviewed for potential roles of, for example, air pollution, pesticides, plastics, prenatal vitamins, lifestyle and family factors, and maternal obstetric and metabolic conditions during her pregnancy. Three examples from the case-control CHildhood Autism Risks from Genes and the Environment Study are probed to illustrate methodological approaches to central challenges in observational studies: capturing environmental exposure; causal inference when a randomized controlled clinical trial is either unethical or infeasible; and the integration of genetic, epigenetic, and environmental influences on development. We conclude with reflections on future directions, including exposomics, new technologies, the microbiome, gene-by-environment interaction in the era of -omics, and epigenetics as the interface of those two. As the environment is malleable, this research advances the goal of a productive and fulfilling life for all children, teen-agers and adults. Autism Res 2018, 11: 554-586. © 2018 International Society for Autism Research, Wiley Periodicals, Inc.

LAY SUMMARY

This Keynote Lecture, delivered at the 2016 meeting of the International Society for Autism Research, discusses evidence from human epidemiologic studies of prenatal factors contributing to autism, such as pesticides, maternal nutrition and her health. There is no single cause for autism. Examples highlight the features of a high-quality epidemiology study, and what comprises a compelling case for causation. Emergent research directions hold promise for identifying potential interventions to reduce disabilities, enhance giftedness, and improve lives of those with ASD.

Autism spectrum disorder and birth spacing: Findings from the study to explore early development (SEED)

Previous studies of autism spectrum disorder (ASD) and birth spacing had limitations; few examined phenotypic case subtypes or explored underlying mechanisms for associations and none assessed whether other (non-ASD) developmental disabilities (DDs) were associated with birth spacing. We assessed associations between inter-pregnancy interval (IPI) and both ASD and other DDs using data from the Study to Explore Early Development, a multi-site case-control study with rigorous case-finding and case-classification methods and detailed data collection on maternal reproductive history. Our sample included 356 ASD cases, 627 DD cases, and 524 population (POP) controls born in second or later births. ASD and DD cases were further sub-divided according to whether the child had intellectual disability (ID). ASD cases were also sub-divided by ASD symptom severity, and DD cases were subdivided by presence of some ASD symptoms (indicated on an autism screener). Odds ratios, adjusted for maternal-child sociodemographic factors, (aORs) and 95% confidence intervals were derived from logistic regression models. Among term births, ASD was associated with both IPI <18 months (aOR 1.5 [1.1-2.2]) and ≥60 months (1.5 [0.99-2.4]). Both short and long IPI associations were stronger among ASD cases with high severity scores (aORs 2.0 [1.3-3.3] and 1.8 [0.99-3.2], respectively). Associations were unchanged after adding several factors potentially related to the causal pathway to regression models. DD was not associated with either short or long IPI-overall, among term births, or in any subgroup examined. These findings extend those from previous studies and further inform recommendations on optimal pregnancy spacing. Autism Res 2018, 11: 81-94. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

LAY SUMMARY

We investigated whether the amount of time between pregnancies was associated autism spectrum disorder (ASD) or other developmental disabilities (DD) in children. ASD was increased in second and later-born children who were conceived less than 18 months or 60 or more months after the mother's previous birth. Other DDs were not associated with birth spacing.

Maternal and Paternal Infertility Disorders and Treatments and Autism Spectrum Disorder: Findings from the Study to Explore Early Development

Previous studies of associations between ASD and conception using assisted reproductive technology (ART) are inconsistent and few studies have examined associations with other infertility treatments or infertility disorders. We examined associations between ASD and maternal/paternal infertility disorders and numerous maternal treatments among 1538 mother-child pairs in the Study to Explore Early Development, a population-based case-control study. ASD was associated with any female infertility diagnosis and several specific diagnoses: blocked tubes, endometriosis, uterine-factor infertility, and polycystic ovarian syndrome. Stratified analyses suggested associations were limited to/much stronger among second or later births. The findings were not explained by sociodemographic factors such as maternal age or education or multiple or preterm birth. ASD was not associated with ART or non-ART infertility treatments.

Environmental risk factors for autism: an evidence-based review of systematic reviews and meta-analyses

BACKGROUND

According to recent evidence, up to 40-50% of variance in autism spectrum disorder (ASD) liability might be determined by environmental factors. In the present paper, we conducted a review of systematic reviews and meta-analyses of environmental risk factors for ASD. We assessed each review for quality of evidence and provided a brief overview of putative mechanisms of environmental risk factors for ASD.

FINDINGS

Current evidence suggests that several environmental factors including vaccination, maternal smoking, thimerosal exposure, and most likely assisted reproductive technologies are unrelated to risk of ASD. On the contrary, advanced parental age is associated with higher risk of ASD. Birth complications that are associated with trauma or ischemia and hypoxia have also shown strong links to ASD, whereas other pregnancy-related factors such as maternal obesity, maternal diabetes, and caesarian section have shown a less strong (but significant) association with risk of ASD. The reviews on nutritional elements have been inconclusive about the detrimental effects of deficiency in folic acid and omega 3, but vitamin D seems to be deficient in patients with ASD. The studies on toxic elements have been largely limited by their design, but there is enough evidence for the association between some heavy metals (most important inorganic mercury and lead) and ASD that warrants further investigation. Mechanisms of the association between environmental factors and ASD are debated but might include non-causative association (including confounding), gene-related effect, oxidative stress, inflammation, hypoxia/ischemia, endocrine disruption, neurotransmitter alterations, and interference with signaling pathways.

CONCLUSIONS

Compared to genetic studies of ASD, studies of environmental risk factors are in their infancy and have significant methodological limitations. Future studies of ASD risk factors would benefit from a developmental psychopathology approach, prospective design, precise exposure measurement, reliable timing of exposure in relation to critical developmental periods and should take into account the dynamic interplay between gene and environment by using genetically informed designs.

Genetic Syndromes, Maternal Diseases and Antenatal Factors Associated with Autism Spectrum Disorders (ASD)

Autism spectrum disorder (ASD) affecting about 1% of all children is associated, in addition to complex genetic factors, with a variety of prenatal, perinatal, and postnatal etiologies. In addition, ASD is often an important clinical presentation of some well-known genetic syndromes in human. We discuss these syndromes as well as the role of the more important prenatal factors affecting the fetus throughout pregnancy which may also be associated with ASD. Among the genetic disorders we find Fragile X, Rett syndrome, tuberous sclerosis, Timothy syndrome, Phelan-McDermid syndrome, Hamartoma tumor syndrome, Prader-Willi and Angelman syndromes, and a few others. Among the maternal diseases in pregnancy associated with ASD are diabetes mellitus (PGDM and/or GDM), some maternal autoimmune diseases like antiphospholipid syndrome (APLS) with anti-β2GP1 IgG antibodies and thyroid disease with anti-thyroid peroxidase (TPO) antibodies, preeclampsia and some other autoimmune diseases with IgG antibodies that might affect fetal brain development. Other related factors are maternal infections (rubella and CMV with fetal brain injuries, and possibly Influenza with fever), prolonged fever and maternal inflammation, especially with changes in a variety of inflammatory cytokines and antibodies that cross the placenta and affect the fetal brain. Among the drugs are valproic acid, thalidomide, misoprostol, and possibly SSRIs. β2-adrenergic receptor agonists and paracetamol have also lately been associated with increased rate of ASD but the data is too preliminary and inconclusive. Associations were also described with ethanol, cocaine, and possibly heavy metals, heavy smoking, and folic acid deficiency. Recent studies show that heavy exposure to pesticides and air pollution, especially particulate matter < 2.5 and 10 μm in diameter (PM2.5 and PM10) during pregnancy is also associated with ASD. Finally, we have to remember that many of the associations mentioned in this review are only partially proven, and not all are "clean" of different confounding factors. The associations described in this review emphasize again how little we know about the etiology and pathogenesis of ASD. It is obvious that we need more epidemiologic data to establish many of these associations, but if proven, they might be promising avenues for prevention.