Interpregnancy interval and risk of autistic disorder

Interpregnancy intervals and behavioural outcomes in children: A population-based longitudinal study

BACKGROUND

While the physical health consequence of short interpregnancy intervals (IPIs) is well documented, its mental health impact is not well explored. This study aimed to examine the associations between IPIs and behavioural outcomes in children born following the interval at four developmental time points between ages 7 and 16.

METHODS

Our study sample comprised participants in the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort, an ongoing population-based longitudinal birth cohort in Bristol, Avon, United Kingdom. Behavioural problems, including total behavioural difficulties, hyperactivity, emotional symptoms, conduct problems, peer-problems, and problems of pro-social behaviour, were assessed using the Strengths and Difficulties Questionnaire (SDQ). Over 2300 mothers and their singleton children were included in this study. Generalized Estimating Equations (GEE) were used to estimate odds ratios for the associations.

RESULTS

Children born to mothers with short IPI (<6 months) were 1.54 (95%CI: 1.12-2.11), 1.42 (95% CI: 1.12-1.81) and 1.37 (95%CI: 1.04-1.79) times more likely to have total behavioural difficulties, conduct problems and hyperactivity/inattention problems across the child's age, respectively, compared with children of mothers with IPIs of 18-23 months. We found no evidence of associations between short IPI (<6 months) and emotional symptoms, peer-relationship problems and pro-social behaviour problems.

CONCLUSION

Short IPI (<6 months) was associated with externalising (conduct and hyperactivity/inattention) but not internalising (emotional and peer-relationship problems) problems. Further studies are needed to confirm this association and elucidate the underlying mechanisms.

A case-control study on pre-, peri-, and neonatal risk factors associated with autism spectrum disorder among Armenian children

We aimed to investigate the role of pre-, peri- and neonatal risk factors in the development of autism spectrum disorder (ASD) among Armenian children with the goal of detecting and addressing modifiable risk factors to reduce ASD incidence. For this purpose a retrospective case-control study using a random proportional sample of Armenian children with ASD to assess associations between various factors and ASD was conducted. The study was approved by the local ethical committee, and parental written consent was obtained. A total of 168 children with ASD and 329 controls were included in the analysis. Multivariable logistic regression analysis revealed that male gender, maternal weight gain, use of MgB6, self-reported stress during the pregnancy, pregnancy with complications, as well as use of labor-inducing drugs were associated with a significant increase in the odds of ASD, whereas Duphaston use during pregnancy, the longer interpregnancy interval and birth height were associated with decreased odds of ASD. These findings are pertinent as many identified factors may be preventable or modifiable, underscoring the importance of timely and appropriate public health strategies aimed at disease prevention in pregnant women to reduce ASD incidence.

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 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.

Environmental Risk Factors in Autism Spectrum Disorder: A Narrative Review

Existing evidence indicates that environmental factors might contribute up to 50% of the variance in autism spectrum disorder (ASD) risk. This structured narrative review offers a comprehensive synthesis of current knowledge on environmental risk factors in ASD, including evaluation of conflicting evidence, exploration of underlying mechanisms, and suggestions for future research directions. Analysis of diverse epidemiological investigations indicates that certain environmental factors, including advanced parental age, preterm birth, delivery complications, and exposure to toxic metals, drugs, air pollutants, and endocrine-disrupting chemicals, are linked to an increased ASD risk through various mechanisms such as oxidative stress, inflammation, hypoxia, and its consequences, changes in neurotransmitters, disruption of signaling pathways and some others. On the other hand, pregnancy-related factors such as maternal diabetes, maternal obesity, and caesarian section show a weaker association with ASD risk. At the same time, other environmental factors, such as vaccination, maternal smoking, or alcohol consumption, are not linked to the risk of ASD. Regarding nutritional elements data are inconclusive. These findings highlight the significance of environmental factors in ASD etiology and emphasize that more focused research is needed to target the risk factors of ASD. Environmental interventions targeting modifiable risk factors might offer promising avenues for ASD prevention and treatment.

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.

Spatial distribution of short birth interval and associated factors among reproductive age women in Ethiopia: spatial and multilevel analysis of 2019 Ethiopian mini demographic and health survey

BACKGROUND

Short Birth Interval negatively affects the health of both mothers and children in developing countries. Studies conducted in Ethiopia on the spatial variation and determinants of individual and community-level factors about short birth intervals were limited. Thus, this study was intended to assess the spatial variation of the short birth interval and its determinants in Ethiopia.

METHODS

This study is a secondary analysis of the Ethiopian Demographic and Health Survey (mini EDHS 2019). A total of 1784 reproductive-age women were included in the analysis. The global spatial autocorrelation (Global Moran's I) and the Getis-Ord statistics tool were used to detect the presence of clustering and the high/low hotspot areas of SBI respectively. Ordinary kriging was used to interpolate short birth intervals, and spatial scan statistics were employed to identify spatial clusters with high and low SBI. A multilevel multivariable model was used to identify predictors of a short birth interval.

RESULTS

The prevalence of SBI was 62.89% (95%CI: 59.3, 69.7) in Ethiopia. High clustering of SBI was observed in all parts of Somali, in Afar (zones 1, 3, 4, &5), Oromia (Guje, Bale, & West Harerge), and northern Tigray. The most likely significant primary cluster was observed in the Somali region. Women who lived in the primary cluster were 24% more likely to have a short birth interval than those who lived outside the window. In the multilevel mixed-effect analysis age 25-34 [(AOR = 0.40, 95% CI: 0.35, 0.45)], 35-49 [(AOR = 0.44, 95% CI: 0.38, 0.51)], Muslim religion follower [(AOR = 3.5, 95% CI: 2.7, 4.69)], no formal education [(AOR = 0.5, 95% CI: 0.37, 0.70)], primary education[(AOR = 0.4, 95%CI: 0.28, 0.53)], and secondary education [(AOR = 0.3, 95% CI: 0.24, 0.48)], middle [(AOR: 1.3, 95% CI: 1.2, 1.52)], rich wealth status [(AOR: 1.4, 95% CI: 1.3, 1.68)], female sex children [(AOR: 1.2, 95% CI: 1.09, 1.42)], and two or fewer ideal number of children [(AOR = 0.2, 95% CI: 0.25, 0.32)] were found to be significant predictors of SBI.

CONCLUSION

Overall, SBI was high and significantly clustered across the region of Ethiopia. Age, religion, education, wealth status, the sex of the indexed child, and the ideal number of children were found to be significantly associated with short birth intervals. Hence, the government should design a health promotion strategy and public health awareness in the identified hotspot areas of SBI and should scale up family planning and the wealth status of reproductive-age women.

Cohort-guided insights into gene-environment interactions in autism spectrum disorders

Prospective birth cohorts offer unprecedented opportunities to investigate the pathogenesis of complex disorders such as autism, in which gene-environment interactions must be appreciated in a temporal context. This Perspective article considers the history of autism research, including missteps that reflected an incomplete understanding of the epidemiology of autistic spectrum disorders, the effects of advocacy and philanthropy on the trajectory of scientific inquiry, and the current and future roles of prospective birth cohort research in illuminating the pathology of these and other complex disorders wherein exposures during gestation might not manifest until later in life.

Schmidt R, N. Pearce E. Prenatal Exposure to Per- and Polyfluoroalkyl Substances, Maternal Thyroid Dysfunction, and Child Autism Spectrum Disorder

Autism spectrum disorder (ASD), with its high economic and societal costs, is a growing public health concern whose prevalence has risen steadily over the last two decades. Although actual increased incidence versus improved diagnosis remains controversial, the increased prevalence of ASD suggests non-inherited factors as likely contributors. There is increasing epidemiologic evidence that abnormal maternal thyroid function during pregnancy is associated with increased risk of child ASD and other neurodevelopmental disorders. Prenatal exposure to endocrine-disrupting chemicals such as per- and polyfluoroalkyl substances (PFAS) is known to disrupt thyroid function and can affect early brain development; thus, thyroid dysfunction is hypothesized to mediate this relationship. The concept of a potential pathway from prenatal PFAS exposure through thyroid dysfunction to ASD etiology is not new; however, the extant literature on this topic is scant. The aim of this review is to evaluate and summarize reports with regard to potential mechanisms in this pathway.

Utilization of Immediate Postpartum Long Acting Reversible Contraceptives among Women Who Gave Birth in Public Health Facilities in Eastern Ethiopia: A Cross-Sectional Study

OBJECTIVE

Although importance of postpartum family planning is essential and immediate postpartum insertion of long acting and reversible contraceptives (LARC) is recommended, evidence on its uptake and associated factors is limited in Ethiopia. This study was conducted to assess utilization of immediate postpartum LARC among women who gave birth in selected public health facilities in eastern Ethiopia.

METHOD

An institution-based cross-sectional study was conducted among randomly selected women who gave birth in selected public health facilities in eastern Ethiopia from 10 March to 09 April 2020. At discharge, all eligible women who gave birth in the facilities were interviewed using a pretested structured questionnaire. Data were entered using EpiData 3.1 and analyzed using SPSS 24. Bivariable and multivariable logistic regression analyses were conducted to identify factors associated with utilization of immediate postpartum LARC. Adjusted odds ratio (aOR) with 95% confidence interval was used to report association, and significance was declared at p value < 0.05.

RESULTS

From a total of 546 women invited to the study, 530 (97.1%) participated in the study and 98 (18.5%; 95% CI: 15.1%, 22.0%) reported starting long acting reversible contraceptives. Women who reported discussing about contraceptives with partners (aOR = 6.69, 95% CI: 3.54, 12.61) and receiving postpartum counselling on contraceptives (aOR = 5.37, 95% CI: 3.00, 9.63) were more likely to using contraception. However, women who live >30-minute walking distance from the nearest health facility (aOR = 0.47, 95% CI: 0.26, 0.85) and reported disrespect and abuse during childbirth (aOR = 0.22, 95% CI: 0.12, 0.40) were less likely to start LARC.

CONCLUSIONS

Almost one in five women delivering in public health facilities in eastern Ethiopia started using LARC. Provision of respectful maternity care including counselling on the importance of immediate postpartum family planning is essential for increasing its uptake.

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.

Increased Risk of ADHD at Short and Long Interpregnancy Intervals in a National Birth Cohort

BACKGROUND

Short or long interpregnancy interval (IPI) may adversely impact conditions for foetal development. Whether attention deficit hyperactivity disorder (ADHD) is related to IPI has been largely unexplored.

OBJECTIVES

To examine the association between IPI and ADHD in a large, population-based Finnish study.

METHODS

All children born in Finland between 1991 and 2005 and diagnosed with ADHD (ICD-9 314x or ICD-10 F90.x) from 1995 to 2011 were identified using data from linked national registers. Each subject with ADHD was matched to 4 controls based on sex, date of birth, and place of birth. A total of 9564 subjects with ADHD and 34,479 matched controls were included in analyses. IPI was calculated as the time interval between sibling birth dates minus the gestational age of the second sibling. The association between IPI and ADHD was determined using conditional logistic regression and adjusted for potential confounders.

RESULTS

Relative to births with an IPI of 24 to 59 months, those with the shortest IPI (<6 months) had an increased risk of ADHD (odds ratio [OR] 1.30, 95% confidence interval (CI) 1.12, 1.51) and the ORs for the longer IPI births (60-119 months and ≥120 months) were 1.12 (95% CI 1.02, 1.24) and 1.25 (95% CI 1.08, 1.45), respectively. The association of longer IPI with ADHD was attenuated by adjustment for maternal age at the preceding birth, and comorbid autism spectrum disorders did not explain the associations with ADHD.

CONCLUSIONS

The risk of ADHD is higher among children born following short or long IPIs although further studies are needed to explain this association.

Association Between Midpregnancy Polyunsaturated Fatty Acid Levels and Offspring Autism Spectrum Disorder in a California Population-Based Case-Control Study

Polyunsaturated fatty acids (PUFAs) are critical for brain development and have been linked with neurodevelopmental outcomes. We conducted a population-based case-control study in California to examine the association between PUFAs measured in midpregnancy serum samples and autism spectrum disorder (ASD) in offspring. ASD cases (n = 499) were identified through the California Department of Developmental Services and matched to live-birth population controls (n = 502) on birth month, year (2010 or 2011), and sex. Logistic regression models were used to examine crude and adjusted associations. In secondary analyses, we examined ASD with and without co-occurring intellectual disability (ID; n = 67 and n = 432, respectively) and effect modification by sex and ethnicity. No clear patterns emerged, though there was a modest inverse association with the top quartile of linoleic acid level (highest quartile vs. lowest: adjusted odds ratio = 0.74, 95% confidence interval: 0.49, 1.11; P for trend = 0.10). Lower levels of total and ω-3 PUFAs were associated with ASD with ID (lowest decile of total PUFAs vs. deciles 4-7: adjusted odds ratio = 2.78, 95% confidence interval: 1.13, 6.82) but not ASD without ID. We did not observe evidence of effect modification by the factors examined. These findings do not suggest a strong association between midpregnancy PUFA levels and ASD. In further work, researchers should consider associations with ASD with ID and in other time windows.

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.

Shorter birth intervals between siblings are associated with increased risk of parental divorce

Birth intervals are a crucial component of fertility behaviour and family planning. Short birth intervals are associated—although not necessarily causally—with negative health-related outcomes, but less is known about their associations with family functioning. Here, the associations between birth intervals and marital stability were investigated by Cox regression using a nationally representative, register-based sample of individuals with two (N = 42,481) or three (N = 22,514) children from contemporary Finland (observation period 1972–2009). Shorter interbirth intervals were associated with an increased risk of parental divorce over a ten-year follow-up. Individuals with birth intervals of up to 1.5 years had 24–49 per cent higher divorce risk compared to individuals whose children were born more than 4 years apart. The pattern was similar in all socioeconomic groups and among individuals with earlier and later entry to parenthood. Our results add to the growing body of research showing associations between short birth intervals and negative outcomes in health and family functioning.

Risk factors and child outcomes associated with short and long interpregnancy intervals

Previous research assessing consequences of interpregnancy intervals (IPIs) on child development is mixed. Utilizing a population-based US sample (n=5,339), we first estimated the associations between background characteristics (e.g., sociodemographic and maternal characteristics) and short (≤ 1 year) and long (> 3 years) IPI. Then, we estimated associations between IPI and birth outcomes, infant temperament, cognitive ability, and externalizing symptoms. Several background characteristics, such as maternal age at childbearing and previous pregnancy loss, were associated with IPI, indicating research on the putative effects of IPI must account for background characteristics. After covariate adjustment, short IPI was associated with poorer fetal growth and long IPI was associated with lower infant activity level; however, associations between short and long IPI and the other outcomes were neither large nor statistically significant. These findings indicate that rather than intervening to modify IPI, at-risk families may benefit from interventions aimed at other modifiable risk factors.

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.

Outcome-dependent associations between short interpregnancy interval and offspring psychological and educational problems: a population-based quasi-experimental study

Background

Causal interpretation of associations between short interpregnancy interval (the duration from the preceeding birth to the conception of the next-born index child) and the offspring's psychological and educational problems may be influenced by a failure to account for unmeasured confounding.

Methods

Using population-based Swedish data from 1973-2009, we estimated the association between interpregnancy interval and outcomes [autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), severe mental illness, suicide attempt, criminality, substance-use problem and failing grades] while controlling for measured covariates. We then used cousin comparisons, post-birth intervals (the interval between the second- and third-born siblings to predict second-born outcomes) and sibling comparisons to assess the influence of unmeasured confounding. We included an exploratory analysis of long interpregnancy interval.

Results

Interpregnancy intervals of 0-5 and 6-11 months were associated with higher odds of outcomes in cohort analyses. Magnitudes of association were attenuated following adjustment for measured covariates. Associations were eliminated for ADHD, severe mental illness and failing grades, but maintained magnitude for ASD, suicide attempt, criminality and substance-use problem in cousin comparisons. Post-birth interpregnancy interval and sibling comparisons suggested some familial confounding. Associations did not persist across models of long interpregnancy interval.

Conclusions

Attenuation of the association in cousin comparisons and comparable post-birth interval associations suggests that familial genetic or environmental confounding accounts for a majority of the association for ADHD, severe mental illness and failing grades. Modest associations appear independently of covariates for ASD, suicide attempt, criminality and substance-use problem. Post-birth analyses and sibling comparisons, however, show some confounding in these associations.

Autism spectrum disorders: let's talk about glucose?

Autism spectrum disorders (ASD) are characterized by disconnectivity due to disordered neuronal migration, and by neuronal mitochondrial dysfunction. Different pathways involved in neuronal migration are affected by intrauterine hyperglycemia and hyperinsulinemia, while prolonged neonatal hypoglycemia may cause mitochondrial dysfunction. Our hypothesis was that conditions leading to intrauterine hyperglycemia or neonatal hypoglycemia would influence ASD pathogenesis. In this study, we identified risk factors for ASD by searching PubMed with the MeSH terms "autism spectrum disorder" and "risk factors". We then analyzed the relationship between the risk factors and glucose abnormalities in the mother and the offspring. The relationship between glucose abnormalities and risk factors such as obesity, excessive maternal weight gain, or diabetes mellitus is evident. For risk factors such as malformations or exposure to selective serotonin reuptake inhibitors, the relationship is speculative. In rodents, for example, intrauterine hyperglycemia is associated with malformations, independent of maternal diabetes. In their turn, selective serotonin reuptake inhibitors reduce the signs of neonatal hypoglycemia. Going undetected, prolonged hypoglycemia may harm the neonatal brain. Importantly, our group demonstrated that either high-carbohydrate diets or physical inactivity the day before delivery may influence neonatal glycemia. In that study, of 158 neonates selected to be screened according to maternal lifestyle risk factors, 48 had hypoglycemia. Of note, five of them had not been identified with current screening programs. Controlled studies are needed to clarify whether maternal interventions aiming at maintaining glycemic control, together with screening programs for neonatal hypoglycemia based on maternal lifestyle risk factors and on exposure to specific prenatal medications can reduce the prevalence of ASD.

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.

Birth Intervals and Health in Adulthood: A Comparison of Siblings Using Swedish Register Data

A growing body of research has examined whether birth intervals influence perinatal outcomes and child health as well as long-term educational and socioeconomic outcomes. To date, however, very little research has examined whether birth spacing influences long-term health. We use contemporary Swedish population register data to examine the relationship between birth-to-birth intervals and a variety of health outcomes in adulthood: for men, height, physical fitness, and the probability of falling into different body mass index categories; and for men and women, mortality. In models that do not adjust carefully for family background, we find that short and long birth intervals are clearly associated with height, physical fitness, being overweight or obese, and mortality. However, after carefully adjusting for family background using a within-family sibling comparison design, we find that birth spacing is generally not associated with long-term health, although we find that men born after very long birth intervals have a higher probability of being overweight or obese in early adulthood. Overall, we conclude that birth intervals have little independent effect on long-term health outcomes.

Polycystic ovary syndrome and autism: A test of the prenatal sex steroid theory

Elevated levels of prenatal testosterone may increase the risk for autism spectrum conditions (autism). Given that polycystic ovary syndrome (PCOS) is also associated with elevated prenatal testosterone and its precursor sex steroids, a hypothesis from the prenatal sex steroid theory is that women with PCOS should have elevated autistic traits and a higher rate of autism among their children. Using electronic health records obtained from the Clinical Practice Research Datalink (CPRD) in the UK between 1990 and 2014, we conducted three matched case-control studies. Studies 1 and 2 examined the risk of PCOS in women with autism (n = 971) and the risk of autism in women with PCOS (n = 26,263), respectively, compared with matched controls. Study 3 examined the odds ratio (OR) of autism in first-born children of women with PCOS (n = 8588), matched to 41,127 controls. In Studies 1 and 2 we found increased prevalence of PCOS in women with autism (2.3% vs. 1.1%; unadjusted OR: 2.01, 95% CI: 1.22-3.30) and elevated rates of autism in women with PCOS (0.17% vs. 0.09%, unadjusted OR: 1.94 CI: 1.37-2.76). In Study 3 we found the odds of having a child with autism were significantly increased, even after adjustment for maternal psychiatric diagnoses, obstetric complications, and maternal metabolic conditions (unadjusted OR: 1.60, 95% CI: 1.28-2.00; adjusted OR: 1.35, 95% CI: 1.06-1.73). These studies provide further evidence that women with PCOS and their children have a greater risk of autism.

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.

Interpregnancy Interval and Adverse Perinatal Outcomes: A Record-Linkage Study Using the Manitoba Population Research Data Repository

OBJECTIVE

To examine the association between the interpregnancy interval (IPI) and preterm birth, low birth weight, and SGA birth in a developed country with universal health coverage.

METHODS

We conducted a secondary analysis of data housed at the Manitoba Centre for Health Policy. All live births in Manitoba hospitals over a 29-year period were identified and consecutive births to the same mother were grouped into sibling pairs to calculate the IPI for the younger siblings. Logistic regression models were fit to examine the association between the IPI and adverse perinatal outcomes, adjusted for potentially confounding sociodemographic and clinical factors.

RESULTS

In a cohort of more than 171 000 births and relative to IPIs of 18 to 23 months, IPIs shorter than 12 and longer than 23 months were associated with significantly increased odds of preterm birth overall and both medically indicated and spontaneous preterm births, low birth weight, and SGA birth. The strongest association observed was for intervals shorter than 6 months and spontaneous preterm birth (adjusted OR 1.83, 95% CI 1.65-2.03). When the outcome was modelled as GA categories, the strongest association observed was for intervals shorter than 6 months and early preterm birth (<34 weeks' GA; adjusted OR 2.47, 95% CI 2.07-2.94).

CONCLUSION

If the associations observed between the IPI and adverse perinatal outcomes in this large, population-based cohort are causal, birth spacing could form an important target of public health messaging in Canada.

The Changing Epidemiology of Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition with lifelong impacts. Genetic and environmental factors contribute to ASD etiology, which remains incompletely understood. Research on ASD epidemiology has made significant advances in the past decade. Current prevalence is estimated to be at least 1.5% in developed countries, with recent increases primarily among those without comorbid intellectual disability. Genetic studies have identified a number of rare de novo mutations and gained footing in the areas of polygenic risk, epigenetics, and gene-by-environment interaction. Epidemiologic investigations focused on nongenetic factors have established advanced parental age and preterm birth as ASD risk factors, indicated that prenatal exposure to air pollution and short interpregnancy interval are potential risk factors, and suggested the need for further exploration of certain prenatal nutrients, metabolic conditions, and exposure to endocrine-disrupting chemicals. We discuss future challenges and goals for ASD epidemiology as well as public health implications.

Fetal origins of autism spectrum disorders: the non-associated maternal factors

Aim:

Several population-based studies have been conducted to determine whether maternal exposures are involved in the pathophysiology of autism spectrum disorder (ASD). We review these studies and describe the factors not associated with increased risk for ASD development.

Methods:

We identified studies describing associations between maternal exposures and ASD development. These studies include the Childhood Autism Risks from Genetics and the Environment, Nurses’ Health Study II, and the Swedish population registry.

Results:

Factors not associated with ASD development include Type 2 and gestational diabetes, chronic hypertension, fever treated with antipyretic medication, autoimmune disease and short interpregnancy intervals.

Conclusion:

There is increasing evidence that maternal exposures are involved in the pathophysiology of ASD in the developing fetus.

Lay Abstract: Autism spectrum disorder currently affects one in 68 children in the USA, with up to one in 42 boys. Its underlying etiology is largely unknown. Although autism was once considered a childhood disease, efforts for early detection led to the realization that it might originate at a much earlier stage, namely fetal life. Several maternal risk factors have recently been studied to establish associations with autism in the offspring. In this review, we present the maternal risk factors that were not found to have such associations.

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

CONTEXT

Both short and long interpregnancy intervals (IPIs) have recently been associated with increased risk of autism spectrum disorder (ASD). However, this association has not been systematically evaluated.

OBJECTIVE

To examine the relationship between birth spacing and the risk of ASD and other neurodevelopmental disabilities.

DATA SOURCES

Electronic databases from their inception to December 2015, bibliographies, and conference proceedings.

STUDY SELECTION

Observational studies with results adjusted for potential confounding factors that reported on the association between IPIs or birth intervals and neurodevelopmental disabilities.

DATA EXTRACTION

Two reviewers independently extracted data on study characteristics, IPIs/birth intervals, and outcome measures.

RESULTS

Seven studies (1 140 210 children) reported an association between short IPIs and increased risk of ASD, mainly the former subtype autistic disorder. Compared with children born to women with IPIs of ≥36 months, children born to women with IPIs of <12 months had a significantly increased risk of any ASD (pooled adjusted odds ratio [OR] 1.90, 95% confidence interval [CI] 1.16-3.09). This association was stronger for autistic disorder (pooled adjusted OR 2.62, 95% CI 1.53-4.50). Three of these studies also reported a significant association between long IPIs and increased risk of ASD. Short intervals were associated with a significantly increased risk of developmental delay (3 studies; 174 940 children) and cerebral palsy (2 studies; 19 419 children).

LIMITATIONS

Substantial heterogeneity, and few studies assessing neurodevelopmental disabilities other than ASD.

CONCLUSIONS

Short IPIs are associated with a significantly increased risk of ASD. Long IPIs also appear to increase the risk of ASD.

Annual Research Review: The role of the environment in the developmental psychopathology of autism spectrum condition

BACKGROUND

Although autism spectrum condition (ASC) is strongly genetic in origin, accumulating evidence points to the critical roles of various environmental influences on its emergence and subsequent developmental course.

METHODS

A developmental psychopathology framework was used to synthesise literature on environmental factors associated with the onset and course of ASC (based on a systematic search of the literature using PubMed, PsychInfo and Google Scholar databases). Particular emphasis was placed on gene-environment interplay, including gene-environment interaction (G × E) and gene-environment correlation (rGE).

RESULTS

Before conception, advanced paternal and maternal ages may independently enhance offspring risk for ASC. Exogenous prenatal risks are evident (e.g. valproate and toxic chemicals) or possible (e.g. selective serotonin reuptake inhibitors), and processes endogenous to the materno-foeto-placental unit (e.g. maternal diabetes, enhanced steroidogenic activities and maternal immune activation) likely heighten offspring vulnerability to ASC. Folate intake is a prenatal protective factor, with a particular window of action around 4 weeks preconception and during the first trimester. These prenatal risks and protective mechanisms appear to involve G × E and potentially rGE. A variety of perinatal risks are related to offspring ASC risk, possibly reflecting rGE. Postnatal social factors (e.g. caregiver-infant interaction, severe early deprivation) during the first years of life may operate through rGE to influence the likelihood of manifesting a full ASC phenotype from a 'prodromal' phase (a proposal distinct to the discredited and harmful 'refrigerator mother hypothesis'); and later postnatal risks, after the full manifestation of ASC, shape life span development through transactions mediated by rGE. There is no evidence that vaccination is a postnatal risk for ASC.

CONCLUSIONS

Future investigations should consider the specificity of risks for ASC versus other atypical neurodevelopmental trajectories, timing of risk and protective mechanisms, animal model systems to study mechanisms underlying gene-environment interplay, large-sample genome-envirome designs to address G × E and longitudinal studies to elucidate how rGE plays out over time. Clinical and public health implications are discussed.

Inter-Pregnancy Intervals and the Risk of Autism Spectrum Disorder: Results of a Population-Based Study

Recent studies have reported an increased risk of autism among second-born children conceived <12 versus >36 months after the birth of a sibling. Confirmation of this finding would point to inter-pregnancy interval (IPI) as a potentially modifiable risk factor for autism. This study evaluated the relationship between IPI and autism spectrum disorder (ASD) risk in a Wisconsin birth cohort of 31,467 second-born children, of whom 160 resided in the study area and were found to have ASD at age 8 years. In adjusted analyses, both short (<12) and long (>84 month) IPIs were associated with a two-fold risk of ASD relative to IPIs of 24-47 months (p < 0.05). The long IPI association was partially confounded by history of previous pregnancy loss.

Interpregnancy Interval and Risk of Autism Spectrum Disorders

OBJECTIVE

To determine whether subsequent births after short and long interpregnancy intervals (IPIs) are associated with risk of autism spectrum disorder (ASD).

METHOD

We assessed the association between IPI and ASD risk in a cohort of 45 261 children born at Kaiser Permanente Northern California (KPNC) between 2000 and 2009. Children with ASD were identified from International Classification of Diseases, Revision 9 diagnostic codes 299.0, 299.8, and 299.9 recorded in KPNC electronic medical records. IPI was defined as the time from the birth of the first child to the conception of the second child. Survival analysis and logistic regression models were used to evaluate the association between IPI and risk of ASD in second-born children.

RESULTS

Children born after an IPI of <12 months or ≥72 months had a 2- to 3-fold increased ASD risk compared with children born after an interval of 36 to 47 months. Respective adjusted hazard ratios (95% confidence intervals) were as follows: <6 months, 3.0 (1.9-4.7); 6 to 8 months, 2.1 (1.4-3.3); 9 to 11 months, 1.9 (1.3-2.1); 12 to 23 months, 1.5 (1.1-2.1); and ≥72 months, 2.4 (1.5-3.7). The results are not explained by maternal BMI or change in BMI between pregnancies or by parental age, maternal antidepressant medication use, or unfavorable events occurring during the first or second pregnancy.

CONCLUSIONS

Children born after interpregnancy intervals <2 years or >6 years may be at increased risk of ASD. The mechanism explaining this association is unknown, and more research is needed.

Recurrence rates provide evidence for sex-differential, familial genetic liability for autism spectrum disorders in multiplex families and twins

Background

Autism spectrum disorders (ASDs) are more prevalent in males, suggesting a multiple threshold liability model in which females are, on average, protected by sex-differential mechanisms. Under this model, autistic females are predicted to carry a more penetrant risk variant load than males and to share this greater genetic liability with their siblings. However, reported ASD recurrence rates have not demonstrated significantly increased risk to siblings of affected girls. Here, we characterize recurrence patterns in multiplex families from the Autism Genetics Resource Exchange (AGRE) to determine if risk in these families follows a female protective model.

Methods

We assess recurrence rates and quantitative traits in full siblings from 1,120 multiplex nuclear families and concordance rates in 305 twin pairs from AGRE. We consider the first two affected children per family, and one randomly selected autistic twin per pair, as probands. We then compare recurrence rates and phenotypes between males and females and between twin pairs or families with at least one female proband (female-containing (FC)) versus those with only male probands (male-only (MO)).

Results

Among children born after two probands, we observe significantly higher recurrence in males (47.5%) than in females (21.1%; relative risk, RR = 2.25; adjusted P = 6.22e−08) and in siblings of female (44.3%) versus siblings of male probands (30.4%; RR = 1.46; adj. P = 0.036). This sex-differential recurrence is also robust in dizygotic twin pairs (males = 61.5%, females = 19.1%; RR = 3.23; adj. P = 7.66e−09). Additionally, we find a significant negative relationship between interbirth interval and ASD recurrence that is driven by children in MO families.

Conclusions

By classifying families as MO or FC using two probands instead of one, we observe significant recurrence rate differences between families harboring sex-differential familial liability. However, a significant sex difference in risk to children within FC families suggests that female protective mechanisms are still operative in families carrying high genetic risk loads. Furthermore, the male-specific relationship between shorter interbirth intervals and increased ASD risk is consistent with a potentially greater contribution from environmental factors in males versus higher genetic risk in affected females and their families. Understanding the mechanisms driving these sex-differential risk profiles will be useful for treatment development and prevention.

Electronic supplementary material

The online version of this article (doi:10.1186/s13229-015-0004-5) contains supplementary material, which is available to authorized users.

Modeling and predicting hemorrhagic fever with renal syndrome trends based on meteorological factors in Hu County, China

Background

Hu County is a serious hemorrhagic fever with renal syndrome (HFRS) epidemic area, with notable fluctuation of the HFRS epidemic in recent years. This study aimed to explore the optimal model for HFRS epidemic prediction in Hu.

Methods

Three models were constructed and compared, including a generalized linear model (GLM), a generalized additive model (GAM), and a principal components regression model (PCRM). The fitting and predictive adjusted R² of each model were calculated. Ljung-Box Q tests for fitted and predicted residuals of each model were conducted. The study period was stratified into before (1971–1993) and after (1994–2012) vaccine implementation epochs to avoid the confounding factor of vaccination.

Results

The autocorrelation of fitted and predicted residuals of the GAM in the two epochs were not significant (Ljung-Box Q test, P>.05). The adjusted R² for the predictive abilities of the GLM, GAM, and PCRM were 0.752, 0.799, and 0.665 in the early epoch, and 0.669, 0.756, and 0.574 in the recent epoch. The adjusted R² values of the three models were lower in the early epoch than in the recent epoch.

Conclusions

GAM is superior to GLM and PCRM for monthly HFRS case number prediction in Hu County. A shift in model reliability coincident with vaccination implementation demonstrates the importance of vaccination in HFRS control and prevention.

Short and long interpregnancy intervals: correlates and variations by pregnancy timing among U.S. women

CONTEXT

Short and long interpregnancy intervals are associated with adverse health outcomes. Little is known about the correlates of short and long interpregnancy intervals in the general population, and whether correlates vary by pregnancy intention.

METHODS

Data on 10,236 pregnancies following a live birth were drawn from the 1995, 2002 and 2006-2010 waves of the National Survey of Family Growth. Logistic regression was used to assess characteristics associated with women's reporting short interpregnancy intervals (less than 12 months) and long intervals (greater than 60 months). Analyses were stratified by whether women considered their pregnancies well timed or mistimed.

RESULTS

Thirty-one percent of pregnancies following short intervals and 47% following long intervals were well timed. Among well-timed pregnancies only, the odds of short intervals were elevated if women had been 35 or older, rather than aged 20-29, at last pregnancy (odds ratio, 2.3); if their prior infant had died (10.6); or if they had wanted their prior pregnancy sooner than it had occurred (2.2). Overall, the odds of long intervals were higher among minority groups than among whites (1.4-1.6) and were lower among women who had been 30 or older at prior pregnancy than among those who had been in their 20s (0.1-0.5); they increased with level of family income. Correlates of long intervals generally varied little by intention.

CONCLUSIONS

Although the majority of pregnancies at short intervals are unintended, specific subsets of women have elevated odds of intending short interpregnancy intervals.

The association between the interpregnancy interval and autism spectrum disorder in a Canadian cohort

OBJECTIVES

Two studies reported an increased risk of autistic disorder in children conceived less than 12 months after a previous birth. Our objective was to examine the association between the interpregnancy interval (IPI) and autism spectrum disorder (ASD) in a Canadian cohort.

METHODS

Using administrative datasets housed at the Manitoba Centre for Health Policy, we identified pairs of first- and second-born singleton siblings born between 1988 and 2005. Diagnoses of ASD were ascertained by searching physician billing claims, hospital discharge abstracts, education data, and a database containing information on individuals identified for a 2002-2007 ASD surveillance program in Manitoba. Logistic regression models were fit to examine the association between the IPI and ASD in 41,050 second-born siblings where the first-borns did not have ASD, using IPIs of ≥ 36 months as the reference category and specifying three case groups. Case Group 1 included individuals with at least one ASD code (n = 490); Case Group 2 included those with two or more ASD codes (n = 375); and Case Group 3 comprised individuals with a record in the ASD surveillance program database (n = 141).

RESULTS

The adjusted odds ratios (ORs) for IPIs shorter than 12 months ranged from 1.22 (95% CI: 0.91-1.63) for Case Group 1 to 1.72 (95% CI: 0.96-3.06) for Case Group 3. When the case groups were restricted to individuals with more severe ASD, the ORs increased and were significant for Case Groups 1 and 2.

CONCLUSION

Our findings also support an association between short IPIs and more severe ASD.

Are Attributes of Pregnancy and the Delivery Room Experience Related to Development of Autism? A Review of the Perinatal and Labor Risk Factors and Autism

Autism is a neurodevelopmental disorder marked by severe deficits in social communication and interactions. It is a complex condition that lacks an established preventive method, warranting a need for research to identify possible environmental triggers. The identification of external factors particularly perinatal risk factors forms the initial critical step in preventing and alleviating risks. We conducted a literature review to assess evidence suggested in the worldwide literature. Perinatal risk factors that have a suggested association include β2 adrenergic receptor agonists, labor induction and augmentation, maternal infection and disease (i.e., antiphospholipid syndrome), antiepileptic drugs, cocaine use, and oral supplements. Smoking has not been found to have a direct association. Pollutants, selective serotonin reuptake inhibitors, artificial insemination, and fertility medications may have a link, but results are often conflicted. Factors related to the delivery room experience may be associated with meconium aspiration syndrome, birth weight, and labor time. Several risk factors during the pregnancy and labor periods have been associated with autism; yet further studies with large populations are needed to establish definitive associations. The fact that several risk factors during the prenatal and labor periods are implicated in autism should prompt the medical community to focus on the pregnancy and labor periods as preventive measures to curb the incidence of autism.

Increased risk of autism spectrum disorders at short and long interpregnancy intervals in Finland

OBJECTIVE

Both short and long interpregnancy intervals (IPI) are believed to present possible adverse conditions for fetal development. Short IPI has recently been associated with increased risk of autism, but whether long IPI increases risk for autism spectrum disorders (ASD) has not been thoroughly investigated. We investigated the association between short and long IPI in a Finnish population-based study.

METHOD

This study was conducted in the Finnish Prenatal Study of Autism, which is based in a national birth cohort. Children born in Finland in 1987 to 2005 and diagnosed with ASD by 2007 were identified through the Finnish Hospital Discharge Register. A total of 2,208 non-firstborn patients with ASD and 5,163 matched controls identified from the Finnish Medical Birth Register were included in the primary analysis. The association between IPI and ASD was determined using conditional logistic regression and adjusted for potential confounders.

RESULTS

Relative to births with an IPI of 24 to 59 months, those with the shortest IPI (<12 months) had an increased risk of ASD (odds ratio [OR] = 1.50, 95% CI = 1.28, 1.74) in confounder-adjusted models, whereas the ORs for longer IPI births (60-119 months and ≥120 months) were 1.28 (95% CI = 1.08, 1.52) and 1.44 (95% CI = 1.12, 1.85), respectively.

CONCLUSION

This study provides evidence that risk of ASD is increased at long as well as short IPI.

Folic acid supplementation and interpregnancy interval

BACKGROUND

Maternal folic acid supplementation between subsequent pregnancies may be important to reduce the risk of low folate status associated with short interpregnancy intervals. We examined how the prevalence of preconception folic acid use for a given pregnancy in Norwegian women varied according to the time interval from the previous pregnancy.

METHODS

Analysis was based on 48 855 pairs of pregnancies with the second pregnancy included in the Norwegian Mother and Child Cohort Study (birth years 1999-2009). Interpregnancy interval was defined as the time from birth of a child to the conception of the subsequent sibling. Preconception folic acid use was defined as any use of folic acid-containing supplements within the last 4 weeks before the second pregnancy.

RESULTS

The prevalence of preconception folic acid use was 31%. Among women with a term birth (≥37 weeks) in the previous pregnancy (92%), those with interpregnancy intervals ≤12 and ≥49 months were associated with up to 35% lower prevalence of preconception folic acid use for the second pregnancy, relative to the reference group (13-24 months). The low use in short intervals was mainly attributable to lower proportion of planned pregnancies and fewer women with higher education. Among women with a preterm birth (<37 weeks) in the previous pregnancy (8%), preconception folic acid use significantly decreased with increasing pregnancy spacing.

CONCLUSIONS

Our finding of a lower preconception folic acid use in women with both short and long interpregnancy intervals might help identifying those with higher risk of folate deficiency and preventing unwanted pregnancy outcomes.