Few women sleep great throughout pregnancy. But a new study shows that poor sleep should be of more concern to doctors and women than is currently recognized because it may be a factor in premature birth.

A number of problems can contribute to preterm birth, such as illness during pregnancy, obesity and stress. But the new study, published Tuesday in the journal Sleep, is the first to show a connection between poor sleep and preterm birth.

Researchers at the University of Pittsburgh School of Medicine looked at sleep and birth outcomes in 166 pregnant women. After controlling for other risk factors that contribute to preterm birth, they found that poor sleep quality in the first trimester and the third trimester was linked to an increased risk of preterm birth with the  largest effects from poor sleep in early pregnancy. It's unclear why there was no connection between sleep problems in the second trimester and preterm birth risk.

Poor sleep has been linked to more inflammation in the body, which may activate processes that lead to early childbirth, the authors said. While preterm birth typically results from a cluster of several risk factors, sleep quality may be something that doctors and their patients can address and improve, the authors noted.