Prenatal and Perinatal Risks Factors for Autism in China

Background: Autism is a multifactorial developmental disorder involving both genetic and environmental factors, but the roles of possible environmental risk factors remain unclear.

Objectives: We investigated the effect of prenatal and perinatal risk factors on autism to identify relevant factors in the etiology and the prevention of this disorder.

Methods: A case-control study was conducted using 95 children with autism from six Special Education Schools and two Preschool Autistic Children Special Education Institutions in Tianjin, China, and 95 controls selected by frequency matching on gender and birth year to the cases from regular schools in the same city. Simple and multiple logistic regression models were used to examine the association between autism and risk factors, and to estimate odds ratios and 95% confidence intervals (CI).

Results: Initial unadjusted analyses with simple logistic regression models were used to screen a long list of potential risk factors. This screening identified numerous variables significantly associated with autism (p<0.05): 10 maternal and fetal conditions during gestation, including maternal second-hand smoke exposure, mother’s emotional state, severe emesis, nuchal cord (umbilical cord wrapped around neck), and 9 characteristics at the time of delivery, such as gestational age < 35 weeks or > 42 weeks, abnormal labor and infant delayed crying. Paternal age (> 30 years old) at delivery and gravidity were also significantly associated with autism. These two factors and the two matching variables (gender and birth year) were used in all multiple logistic regression models and the other potential risk factors were examined one-by-one. After adjusting for gender, birth year, paternal age at delivery and gravidity, all the above 19 significant risk factors remained significantly associated with autism. The following factors had an especially strong association with autism: 1. during pregnancy: maternal unhappy emotional state (OR=3.01, 95% CI: 1.26,7.23, p=0.01), nuchal cord (OR=8.51, CI: 2.70, 26.86, p=0.00), maternal chronic or acute illness (not pregnancy involved) (OR=3.69, 95% CI: 1.30,10.51, p=0.01), maternal second-hand smoke exposure (OR=5.39, 95% CI: 1.72,16.92, p=0.004); 2. at delivery: abnormal gestational age (OR=4.44, 95% CI: 1.71, 11.49, p = 0.002), non-normal labor (OR=2.12, 95% CI: 1.10,4.08, p=0.02) and newborn complication (OR=16.39, 95% CI: 4.78,56.17, p=0.000).

Conclusions: These findings suggest several prenatal and perinatal environmental factors are associated with the risk of autism in children. These specific results may indicate a role for fetal hypoxia, neurotransmitter dysregulation, hormonal, and underlying genetic or chromosomal abnormalities in the etiology of autism.