Washington, Oct 31 Professional singers find it difficult to strike the right note during pregnancy because of hormonal changes, says a new study.

Until recently, researchers did not know if this effect is due to hormones or to some other cause, such as decreased lung capacity as the baby grows.

And to assess the effect of hormones on a pregnant singer's voice, Filipa La of Aveiro University in Portugal followed a professionally-trained Portuguese singer through 12 weeks of pregnancy and for 12 weeks after birth.

Once a week, including just two days after the baby was born, La recorded the singer reading and singing into a device that measures the pressure exerted to make each sound.

Collaborating with Johan Sundberg of KTH in Stockholm, Sweden, La reconciled the data with measurements of the singer's hormone levels.

This was the first longitudinal study of the effect of hormones on a singer's voice during pregnancy, and the researchers found that the increased levels of hormones correlated with changes to the singer's vocal folds.

Though temporary, the changes forced the singer to exert more pressure from her lungs to make the same notes.

"It seems that it's harder work during pregnancy to sing," said La.

However, she added that this is preliminary research based on a single case study and that larger studies would be needed before doctors could give solid advice to professional singers.

The findings of the study will be presented at a meeting of the Acoustical Society of America (ASA) in San Antonio, TX. (ANI)