Obsessive-compulsive disorder that surfaces during adolescence or early adulthood may actually have origins in the circumstances surrounding pregnancy and infancy, a Swedish study suggests.

Smoking during pregnancy, cesarean section delivery, preterm birth, unusually low or high weight at birth and breech presentation at labor were all associated with an increased risk of obsessive-compulsive disorder (OCD) later in life, the study found.

"Children who were born prematurely and to mothers who experienced serious problems with labor and delivery were at increased risk to develop OCD many, many years later," Dr. James Leckman, author of an accompanying editorial, said by email.

Although OCD runs in families and is one of the most inherited psychiatric disorders, no one gene is responsible, added Leckman, a psychiatry researcher at Yale University School of Medicine in New Haven, Connecticut.

The current study sheds new light on potential environmental risk factors for OCD, Leckman said.

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Researchers examined data from a population-based birth cohort of 2.4 million Swedish children born from 1973 to 1996 and followed up through 2013.

This group included about 17,000 people diagnosed with OCD, on average when they were around 23 years old.

Within the birth cohort, researchers also looked at about 11,500 families with siblings that included at least one child with OCD and one without the diagnosis.

By doing this, researchers could look at differences among kids with similar genetic makeup and family circumstances that might help explain the development of OCD later in life.

When mothers smoked at least 10 cigarettes a day during pregnancy, the risk of OCD in their child increased by 27 percent, researchers report in JAMA Psychiatry.

A low Apgar score, which measures things like respiration, pulse and movements after birth, was linked to a 50 percent greater risk of OCD.

Breech babies, who are positioned feet down instead of head down in the uterus, had a 35 percent increased risk of OCD, while cesarean deliveries were associated with a 17 percent greater risk.

Overall, almost half of the people diagnosed with OCD during the study period had at least one risk factor from pregnancy or infancy, and many of them had more than one. The more of these perinatal risk factors a person had, the higher their risk of OCD.

The mechanism linking OCD to factors around the time of birth remains unknown, the authors point out. They note that adverse conditions during fetal development may subtly alter brain development and that some of the same risk factors emerging in this study, like low birthweight and being small for gestational age, have also been linked to increased risk for autism and ADHD.

One limitation of the study is that it focused more on severe cases of OCD that may not represent the entire population of people with this condition, they note in their report. The data only includes people who saw specialists for OCD, and not patients diagnosed by general practitioners.

Even so, the findings bring scientists one step closer to understanding the biological underpinnings of OCD and may eventually lead to treatments to prevent the debilitating effects of this common disorder, Leckman said.

"These findings have real public health significance," Leckman added. "This is especially true of the increased risk associated with heavy maternal smoking during pregnancy, but it is also clear that as a society we need to make sure that all mothers and newborns have optimal medical care."