Nov. 6 (HealthDay News) -- Hormonal fluctuations make it harder for women to sing during pregnancy, a new study finds.

Many professional singers have difficulty singing while pregnant, but it hasn't been known whether this was because of hormones or other causes, such as decreased lung capacity as the baby grows.

In this study, researchers followed a professionally trained singer through 12 weeks of pregnancy and for 12 weeks after she gave birth. Once a week, the singer was recorded reading and singing into a device able to measure the pressure exerted to make each sound. This data was then matched with measurements of the singer's hormone levels.

The researchers found that increased levels of hormones during pregnancy correlated with changes to the singer's vocal folds. These temporary changes forced the singer to use more pressure from her lungs to sing the same notes as when she wasn't pregnant.

"It seems that it's harder work during pregnancy to sing," study author Filipa La of Aveiro University in Portugal, said in a news release from the American Institute of Physics. But she added that this is a single case study, and larger studies need to be done before doctors could give reliable advice to professional singers.

The study was presented recently at the meeting of the Acoustical Society of America, in San Antonio, Texas.

SOURCE: American Institute of Physics, news release, Oct. 27, 2009