Infants may be experiencing sleep difficulties due to marital instability as early as nine months old, according to a new study by an Oregon State University researcher.

“We found that marital instability at nine months old leads to sleep problems at 18 months in infants,” said Anne Mannering, researcher and instructor in the human development and family sciences department at Oregon State.

Mannering explained that even when infants can’t comprehend what is going on, it still influences them on a subconscious level.

Mannering started her research when she was working on a larger project through the Oregon Social Learning Center. This is where Mannering and her collaborators collected research. The study took place over a three-year time period.

The researchers followed more than 350 families starting when their babies were nine months old and continuing until they were 18 months old; a total of nine months.

The goal of the research project was to look at the relationship between marital instability, such as contemplating divorce, and the effects of that instability on children’s sleep. Problems can include falling asleep, staying asleep or frequent night waking.

“We were looking only at adopted families,” Mannering said. “Most studies have looked at biological studies.”

Being one of the first groups to research adopted infants eliminated the role of shared genes between parents and children. The couples were also mostly middle class, white, fairly educated and all had adopted their child within three months of birth.

The findings of marital instability and poor infant sleep remained constant when factoring in birth order, parental anxiety and infant fussiness.

“Stress in the family system in marriage can develop earlier than people think,” Mannering said. “Parents should be aware that marital stress may affect the well-being of their children even in the first year or two of life.”

The study did not find the opposite to be true. Children’s sleep problems did not predict marital instability.

Marital instability was assessed by questions that asked husband and wives individually whether they had considered getting a divorce. The higher the couple scored on the survey, meaning marital instability, the higher the likelihood for the couple to report their children having sleep problems.

This was a national study with contributions from State University, University of New Orleans and Yale Child Study, and the findings of the research will appear in the journal “Child Development.”