Declining levels of erythrocyte folate during the postpartum period among Hispanic women living on the Texas-Mexico border

Birth spacing and risk of adverse pregnancy and birth outcomes: A systematic review and dose-response meta-analysis

INTRODUCTION

The association between extreme birth spacing and adverse outcomes is controversial, and available evidence is fragmented into different classifications of birth spacing.

MATERIAL AND METHODS

We conducted a systematic review of observational studies to evaluate the association between birth spacing (i.e., interpregnancy interval and interoutcome interval) and adverse outcomes (i.e., pregnancy complications, adverse birth outcomes). Pooled odds ratios (ORs) with 95% confidence intervals (CI) were calculated using a random-effects model, and the dose-response relationships were evaluated using generalized least squares trend estimation.

RESULTS

A total of 129 studies involving 46 874 843 pregnancies were included. In the general population, compared with an interpregnancy interval of 18-23 months, extreme intervals (<6 months and ≥ 60 months) were associated with an increased risk of adverse outcomes, including preterm birth, small for gestational age, low birthweight, fetal death, birth defects, early neonatal death, and premature rupture of fetal membranes (pooled OR range: 1.08-1.56; p < 0.05). The dose-response analyses further confirmed these J-shaped relationships (pnon-linear  < 0.001-0.009). Long interpregnancy interval was only associated with an increased risk of preeclampsia and gestational diabetes (pnon-linear  < 0.005 and pnon-linear  < 0.001, respectively). Similar associations were observed between interoutcome interval and risk of low birthweight and preterm birth (pnon-linear  < 0.001). Moreover, interoutcome interval of ≥60 months was associated with an increased risk of cesarean delivery (pooled OR 1.72, 95% CI 1.04-2.83). For pregnancies following preterm births, an interpregnancy interval of 9 months was not associated with an increased risk of preterm birth, according to dose-response analyses (pnon-linear  = 0.008). Based on limited evidence, we did not observe significant associations between interpregnancy interval or interoutcome interval after pregnancy losses and risk of small for gestational age, fetal death, miscarriage, or preeclampsia (pooled OR range: 0.76-1.21; p > 0.05).

CONCLUSIONS

Extreme birth spacing has extensive adverse effects on maternal and infant health. In the general population, interpregnancy interval of 18-23 months may be associated with potential benefits for both mothers and infants. For women with previous preterm birth, the optimal birth spacing may be 9 months.

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.

Maternal lifestyle and environmental risk factors for autism spectrum disorders

BACKGROUND

Over the past 10 years, research into environmental risk factors for autism has grown dramatically, bringing evidence that an array of non-genetic factors acting during the prenatal period may influence neurodevelopment.

METHODS

This paper reviews the evidence on modifiable preconception and/or prenatal factors that have been associated, in some studies, with autism spectrum disorder (ASD), including nutrition, substance use and exposure to environmental agents. This review is restricted to human studies with at least 50 cases of ASD, having a valid comparison group, conducted within the past decade and focusing on maternal lifestyle or environmental chemicals.

RESULTS

Higher maternal intake of certain nutrients and supplements has been associated with reduction in ASD risk, with the strongest evidence for periconceptional folic acid supplements. Although many investigations have suggested no impact of maternal smoking and alcohol use on ASD, more rigorous exposure assessment is needed. A number of studies have demonstrated significant increases in ASD risk with estimated exposure to air pollution during the prenatal period, particularly for heavy metals and particulate matter. Little research has assessed other persistent and non-persistent organic pollutants in association with ASD specifically.

CONCLUSIONS

More work is needed to examine fats, vitamins and other maternal nutrients, as well as endocrine-disrupting chemicals and pesticides, in association with ASD, given sound biological plausibility and evidence regarding other neurodevelopmental deficits. The field can be advanced by large-scale epidemiological studies, attention to critical aetiological windows and how these vary by exposure, and use of biomarkers and other means to understand underlying mechanisms.

Effects of birth spacing on maternal, perinatal, infant, and child health: a systematic review of causal mechanisms

This systematic review of 58 observational studies identified hypothetical causal mechanisms explaining the effects of short and long intervals between pregnancies on maternal, perinatal, infant, and child health, and critically examined the scientific evidence for each causal mechanism hypothesized. The following hypothetical causal mechanisms for explaining the association between short intervals and adverse outcomes were identified: maternal nutritional depletion, folate depletion, cervical insufficiency, vertical transmission of infections, suboptimal lactation related to breastfeeding-pregnancy overlap, sibling competition, transmission of infectious diseases among siblings, incomplete healing of uterine scar from previous cesarean delivery, and abnormal remodeling of endometrial blood vessels. Women's physiological regression is the only hypothetical causal mechanism that has been proposed to explain the association between long intervals and adverse outcomes. We found growing evidence supporting most of these hypotheses.

Effect on risk of anencephaly of gene-nutrient interactions between methylenetetrahydrofolate reductase C677T polymorphism and maternal folate, vitamin B12 and homocysteine profile

OBJECTIVE

To evaluate the effects on anencephaly risk of the interaction between the maternal profile of folate, vitamin B12 and homocysteine and the 677C→T polymorphism in the gene encoding methylenetetrahydrofolate reductase (MTHFR).

DESIGN

Case-control study paired (1:1) on maternity clinic, date of birth and state of residence. Cases of anencephaly were identified using the Registry of the Mexican Neural Tube Defect Epidemiological Surveillance System. Case and control mothers were selected from the same maternity departments. All mothers completed a structured questionnaire and blood samples were obtained to determine the MTHFR 677C→T polymorphism and biochemical profile.

SETTING

Mexico, Puebla and Guerrero states, Mexico.

SUBJECTS

A total of 151 mothers of cases and controls were enrolled from March 2000 to February 2001. We had complete information on biochemical profile and MTHFR C677T polymorphism for ninety-eight mothers of cases and ninety-one mothers of controls.

RESULTS

The adjusted models show that the risk of anencephaly in mothers with 677TT genotype was reduced by 18 % (OR = 0·82; 95 % CI 0·72, 0·94) for each 1 ng/ml increment in serum folate. In terms of tertiles, mothers with 677TT genotype with serum folate levels in the upper tertile (>14·1 ng/ml) had a 95 % lower risk to have a child with anencephaly than mothers with serum folate levels in the first and second tertiles (P trend = 0·012).

CONCLUSIONS

Our data agree with the hypothesis of a gene-nutrient interaction between MTHFR 677C→T polymorphism and folate status. We observed a protective effect on anencephaly risk only in mothers with 677TT genotype as serum folate levels increased.

Pre-conception inter-pregnancy interval and risk of schizophrenia

It is hypothesised that the risk of schizophrenia may be elevated in children conceived following a short inter-pregnancy interval, when maternal folate stores are still being replenished. We examined the relationship between inter-pregnancy interval and schizophrenia risk in a longitudinal, population-based cohort. Risk of schizophrenia was increased by approximately 150% in those born following a pregnancy interval of ≤6 months, but was not increased if the interval after birth of the participant, before conception of the subsequent sibling, was ≤6 months. These findings support the hypothesis that folate (or other micronutrient) deficiency during fetal development may be an important risk factor for schizophrenia.

Closely spaced pregnancies are associated with increased odds of autism in California sibling births

OBJECTIVE

To determine whether the interpregnancy interval (IPI) is associated with the risk of autism in subsequent births.

METHODS

Pairs of first- and second-born singleton full siblings were identified from all California births that occurred from 1992 to 2002 using birth records, and autism diagnoses were identified by using linked records of the California Department of Developmental Services. IPI was calculated as the time interval between birth dates minus the gestational age of the second sibling. In the primary analysis, logistic regression models were used to determine whether odds of autism in second-born children varied according to IPI. To address potential confounding by unmeasured family-level factors, a case-sibling control analysis determined whether affected sibling (first versus second) varied with IPI.

RESULTS

An inverse association between IPI and odds of autism among 662 730 second-born children was observed. In particular, IPIs of <12, 12 to 23, and 24 to 35 months were associated with odds ratios (95% confidence intervals) for autism of 3.39 (3.00-3.82), 1.86 (1.65-2.10), and 1.26 (1.10-1.45) relative to IPIs of ≥ 36 months. The association was not mediated by preterm birth or low birth weight and persisted across categories of sociodemographic characteristics, with some attenuation in the oldest and youngest parents. Second-born children were at increased risk of autism relative to their firstborn siblings only in pairs with short IPIs.

CONCLUSIONS

These results suggest that children born after shorter intervals between pregnancies are at increased risk of developing autism; the highest risk was associated with pregnancies spaced <1 year apart.

Addressing Limited English Proficiency and Disparities for Hispanic Postpartum Women

The National Institutes of Health Office of Minority Health challenges health providers to eliminate health disparities for Hispanic women, especially those women with limited English proficiency. This article addresses this challenge by identifying areas of health disparities for low-risk postpartum Hispanic women with limited English proficiency, by describing the legal basis for improving language access, and by proposing implementation of Office of Minority Health national guidelines. Health providers can use a social equity framework to support improvements in communication practices when language differs.

Association between short birth intervals and schizophrenia in the offspring

Pregnancy burdens maternal folate reserves. Postpartum restoration to normal folate values may take up to 1 year. Maternal folate deficiency during early pregnancy has been hypothesized as a cause of schizophrenia in the offspring. We investigated whether the risk of schizophrenia is increased in persons conceived shortly after another birth. A population-based cohort was established of 1.43 million persons born in Denmark between 1950 and 1983, yielding 17.6 million person-years of follow-up. Schizophrenia in cohort members (5095 cases) and their siblings and parents was identified by linkage with the Danish Psychiatric Case Register. Relative risks of schizophrenia were estimated by use of log-linear Poisson regression. As compared to intervals of 45 months and longer, the schizophrenia risk ratio was 1.14 (95% confidence interval [CI], 0.97 to 1.35) for interbirth intervals of up to 15 months, 1.32 (95% CI, 1.12 to 1.56) for intervals of 15 to 17 months, 1.38 (95% CI, 1.18 to 1.61), for intervals of 18 to 20 months and 1.13 (95% CI, 1.00 to 1.29) for intervals of 21 to 26 months. Relative risks did not essentially change after adjustment for age, sex, calendar year of diagnosis, maternal and paternal age, history of mental illness in a parent or sibling, sibship size, place of birth, and distance to younger sibling. These results show an association between short birth intervals and schizophrenia in the offspring. Although maternal folate depletion may play a role in this association, we cannot rule out other explanations such as maternal stress during pregnancy and childhood infections.

Folic Acid Use by Women Receiving Routine Gynecologic Care

OBJECTIVE

Many health professional groups recommend folic acid supplementation for all women able to become pregnant. In this study, we document folic acid supplement use among a sample of women receiving routine gynecologic care.

METHODS

A short questionnaire was administered to 322 women aged 18-45 years who were seeking routine gynecologic care at participating clinics in Little Rock, Arkansas. Questions covered knowledge and use of folic acid supplements, pregnancy intention, and demographic and socioeconomic characteristics. Primary study outcomes were self-reported folic acid awareness, daily or weekly use of folic acid supplements, and intention to begin taking folic acid. Factors affecting study outcomes were examined individually by computing crude odd ratios and adjusted for other covariates using unconditional logistic regression.

RESULTS

Although 61.8% of women reported awareness of the association between folic acid and birth defects prevention, only 27.1% of these women, and 22.7% of all study participants, reported daily use of a folic acid supplement. Substantially more women (39.8%) were taking a folic acid supplement at least once per week. Age, race, educational level, folic acid awareness, marital status, pregnancy intent, and other preventive health behaviors were the most important predictors of compliance.

CONCLUSION

The results indicate a need for targeted interventions directed toward minority women, young women, and those of lower socioeconomic and educational status. The routine gynecologic visit is an ideal opportunity to counsel women of reproductive age to take folic acid daily.

LEVEL OF EVIDENCE

III