They explained their finding by giving an example - infants born to depressed moms sleep more during the day, take much longer to settle down to sleep at night, and wake up more often during the night.
The researchers said that not only does this add to parents' sleepless nights, but also it may help set these children up for their own depression later in life.
Roseanne Armitage, Ph.D., the leader of the U-M Sleep and Chronophysiology Laboratory team at the U-M Depression Center, however, said that this doesn't mean that babies born to depressed moms are doomed to follow in their mothers' shoes, even though depression does tend to run in families.
Nor does it mean that parents who haven't suffered depression can ignore the importance of their babies' sleep.
Instead, it means that all parents - especially ones with a history of depression - must pay close attention to the conditions they create for their infant's sleep, from birth, she added.
"Keeping a very regular sleep schedule is incredibly important. We know that for both children and adults, and from this study we now know that for infants, the more stable the bedtime the less chaotic sleep is during the night," said Armitage.
The research is based on sleep studies involving two groups of new mothers and their babies.
One group was made up of mothers who sought help for depression during pregnancy from the U-M Depression Center's Women's Mood Disorders Program.
The other group was mothers who had no past or current depression. Each group agreed to wear wristwatch-like devices called actigraphs, which measure sleep time at night, light exposure and daytime activity/rest patterns.
The moms began wearing the devices during the last trimester of pregnancy, and then after their babies were born the team fitted each child with a tiny actigraph at the age of two weeks. Then, the team downloaded the information from the devices every month until the babies were eight months old.
So far, the analysis of the data they collected show that babies born to depressed moms had little or no evidence of an in-born 24-hour circadian rhythm soon after they were born - unlike the babies born to women who weren't depressed. This irregular pattern continued until the study ended in the babies' eighth month.
"We think we've identified one of the risk factors that may contribute to these infants' going on to develop depression later in life. Not everybody who has poor sleep or weak circadian rhythms will develop depression, but if sleep stays consistently disrupted and circadian rhythms are weak, the risk is significantly elevated," Armitage said.
The study will be presented at the European Sleep Research Society meeting in Glasgow, Scotland.