The Causes of Autism

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2019- Prenatal Environment and Perinatal Factors Associated with Autism Spectrum Disorder

Journal: Global Clinical and Translational Research, July 2019; Full Article Here

Who are the authors?

Jianjun Ou1,2,3, Yidong Shen1, Yamin Li4, Guanglei Xun5, Huaqing Liu6, Yiqun He7, Hui Guo3, Renrong Wu1, Claude Hughes8, Kun Xia3, Jingping Zhao1, Fengyu Zhang1,2,6

1 Department of Psychiatry & Mental Health Institute of the Second Xiangya Hospital, Central South University; The China National Clinical Research Center for Mental Health Disorders; National Technology Institute of Psychiatry; Key Laboratory of Psychiatry and Mental Health of Hunan Province, Changsha, Hunan, China.
2 Global Clinical and Translational Research Institute, Bethesda, Maryland, USA.
3 Center for Medical Genetics and School of Life Sciences, Central South University, Changsha, Hunan , China.
4 Clinical Nursing Teaching and Research Section, the Second Xiangya Hospital, Central South University, Hunan , China.
5 Shandong Mental Health Center, Jinan, Shandong, China.
6 Peking University Clinical Medical School and Beijing Huilongguan Hospital , Changping District, Beijing, China.
7 The First Department of Clinical Psychosomatic Medicine of the Second Affiliated Hospital of Xinxiang Medical University, Xinxiang, Henan, China
8 Therapeutic Science and Strategy Unit, IQVIA, Research Triangle Park, N C; Department of Obstetrics and Gynecology, Duke University Medical Center. Morrisville, NC, USA.

Are there A.K.A.s to be aware of?

The following terms are not defined in the study: ‘mild emotional problem,’ ‘severe emotional problem,’ ‘traumatic event,’ ‘chemical exposure,’ and ‘maternal infection.’

Why was the study/article written?

The authors wished to identify new environmental factors associated with autism, such as maternal exposure to chemicals during the fetal and perinatal period. The authors cite previous studies that have found the following factors associated with autism: prenatal stress, maternal infection, maternal conditions and perinatal characteristics, such as threatened abortion, abnormal term of delivery, cesarean delivery; a meta analysis is cited in which 40,000 autism cases showed an association of prenatal infections with the risk of autism. Prenatal exposure to air pollution or indoor renovation show an increased risk of intrauterine inflammation and early childhood ear infection. Thus, the authors conducted the present study to determine new environmental factors associated with autism.

What is the study/article about?

The authors conducted a questionnaire using two independent samples of children from south China and north China. The parents received a questionnaire, which asked questions regarding the general conditions of the children, parents’ maternal pregnant and prenatal conditions, the child’s development, history of diseases, medications, history of pregnancy and prenatal exposure to adverse events, history of abortions and diseases, and so on. The study found two new risk factors: maternal chemical exposure and induced abortion are associated with increased risk of autism. The authors conclude that these factors are common and preventable through various means, such as reducing environmental exposure, improving reproductive health, or increasing access to contraceptives.

Photo by Leah Kelley on

When was the data collected; or when did study take place?

Between January 2008 and December 2016

Where did study take place; where was information gathered from?

South sample was from Changsha, Hunan. The north sample was mostly from Qingdao, Shandong.

Initial samples of the autism group and neurotypical group came from the national research program on the genetic study of autism. The second sample was collected to serve as a replication sample.

How did they collect and analyze the data?

Data Collection

Families that had already been recruited for genetic studies from multiple public and private schools for special education and hospital outpatient clinics were contacted for participation in the study. Children with an “inconsistent diagnosis of Asperger” were excluded from the study. Typical children without a family history of autism were recruited from kindergarten classes as controls, and were from the same or an adjacent province and matched for age with the autism sample.

A structured questionnaire was used that asked questions regarding the general conditions of the children, parents’ maternal pregnant and prenatal conditions, the child’s development, history of diseases, medications, history of pregnancy and prenatal exposure to adverse events, history of abortions and diseases, such as maternal infection and use of medication during pregnancy, birth or perinatal conditions. Teachers or research associates sent the questionnaire to the parents, and they were later contacted by someone to complete the questionnaire and other forms. Parental age and level of parental education was used to control for confounding variables.

Total Sample Size

584 with autism in 1st sample; 821 with autism in 2nd sample.

414 typically developing in 1st sample; 489 in 2nd sample.


Cross-tabulation using the Chi-Square or Fisher’s exact test. Stepwise Logistic Regression. Nagelkerke’s R2 measured the variation in the risk of disease explained by risk factors in logistic regression.”

What did the researchers find?

Moms of children with autism were more likely to: have had an induced abortion previously, had chemical exposures, infections, use of medications, a threatened abortion, a traumatic event, an abnormal term of delivery, cesarean delivery, and a mild or severe emotional problem.

Stepwise logistic regression analysis the following factors were significantly associated with autism: chemical exposure, used medication, threatened abortion, maternal infection, induced abortion before having the child, and having suffered from a traumatic event.

For a full list of the findings, read the full article linked above.

Findings Summary

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Maternal chemical exposure, use of medication, maternal infection, threatened abortion, induced abortion, and maternal psychological stress during pregnancy were associated with autism. The first 5 of these explained 10-15% of variation in the risk of autism in both samples, and 16% in combined sample. A significant interaction between maternal infection and medication use was found. These results are consistent with previous studies.

Two new risk factors were identified in the study: maternal chemical exposure and induced abortion.

What do the authors suggest people do with the information?


The authors conclude the article by discussing environmental air pollution, and cite studies discussing how it affects the central nervous system. They also cite how traffic-related pollution exposure during gestation and the first year of life have already been associated with the risk of autism in other studies. They highlight that their study provides new evidence regarding the interactive effect of maternal infection and medication on autism.

Regarding Abortion

The authors cite a study conducted in the United States in 1999 with a small sample size that also found an association between autism and abortions. They explain this association through other studies that found that an induced abortion is associated with a preterm birth in alternate research studies, which in turn, carry a significant risk of autism. In other words, having an abortion increases the likelihood of having a preterm birth, and having a preterm birth increases the likelihood of having a child with autism.

The authors conclude the study by indicating that improving access to contraceptives and reducing chemical exposure, and as well as caution when treating maternal infection should be undertaken.

Shh. Quiet in the hall.

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