A class of antidepressants, known as selective serotonin reuptake inhibitors (SSRIs), are potentially riskier early on in a pregnancy, a study shows.

Children who were exposed to these drugs during the first trimester were nearly four times as likely to develop an autism spectrum disorder (ASD) compared with unexposed children, according to the study found in the Archives of General Psychiatry. The study included fewer than 300 children with a diagnosed ASD and does not prove that taking SSRIs during pregnancy directly causes ASDs, which affect approximately 1 percent of children in the U.S.

From this morning ...

It's a known fact that Autism, which experts refer to as a complex disorder that disrupts social, communicative, and cognitive development, is influenced by genes, but a recent study showed certain environmental factors that could contribute to the disorder significantly - researchers say it may play as large as a role to genes in causing the condition found in twins.

The study, published in the Archives of General Psychiatry, did not specify which environmental factors were at the root of the disorder, however, previous research has shown an increase in risks of maternal and paternal age, low birth weight, multiple pregnancies and any medications, such as antidepressants, that could contribute to exposure to Autism Spectrum Disease, or ASD, during pregnancy.

Researchers found that shared environmental influences may account for as much as 55 percent of a risk of autism, while less than 40 percent can be attributed to genes from a test group of roughly 298 cases of children with Autism, and 1,507 children who were randomly drawn from the Kaiser Permanente Medical Care Program in Northern California.

This is a very significant study because it confirms that genetic factors are involved in the cause of the disorder, Dr. Peter Szatmari, an autism researcher who heads the child psychiatry and behavioral neuroscience department at McMaster University in Ontario, told The New York Times. But it shifts the focus to the possibility that environmental factors could also be really important.

According to the study, a diagnosis of autism, which affects at least 1 percent of children, is made during early childhood, with symptoms manifesting within the first 3 years of life. Over the last three decades, there has been an increase in the prevalence of autism, from four out of five per 10,000 children in the 1960s to roughly 40 each 10,000 children to date, researchers say.