A mother's employment status could be linked to their children's weight over time, according to a recent study.

Researchers from the University of Illinois at Urbana-Champaign found that the majority of preschoolers of working moms may not be getting the amount of sleep they need each night, placing them at higher risk of being overweight or obese within a year.

"The only factor of the four that we investigated that mediated the relationship between maternal employment status and child obesity was how much sleep the child was getting each night," Katherine E. Speirs, lead author of the study, said in a statement.

For the study, researchers followed 247 mother-child pairs from the STRONG Kids study. 
The children, who ranged from 3 to 5 years old, were weighed, measured and had their body mass index calculated at the outset of the study and again one year later.

At the second weigh-in, 17 percent of the preschoolers were overweight and 12 percent were obese, according to BMI-for-age growth charts. 

Sixty-six percent of the mothers in the sample were employed full time, defined as working 35 hours or more per week. Another 18 percent of the women were employed part time, or 20 to 34 hours per week. 

Children whose mothers worked full time got fewer hours of sleep than peers whose mothers worked less than 20 hours per week. The children of women who worked full time also tended to have higher BMIs at the second weigh-in.

Just 18 percent of the preschoolers in the sample were getting the 11 to 12 hours of nightly sleep recommended by the National Heart, Lung and Blood Institute, the researchers found.

On average, the children were getting about 9.6 hours of nighttime sleep. Each additional hour of nighttime sleep that a child obtained was associated with a 6.8 percent decrease in their BMI at the second weigh-in, the researchers found.

"We looked at nighttime sleep in particular, because studies show that the amount of nighttime sleep matters for regulating weight," researcher Janet Liechty said in a statement.

"We think that it might be the more hours that mothers are working, the less time they have, and there may be some sort of tradeoff going on, 'Do I spend quality time with my child or do we get to bed early?'" Speirs said. "And then in the morning, when mothers leave for work, their children also wake up early to get to day care."

The findings are detailed in the journal Sleep Medicine.