Women are twice as likely to snore when they are in the final stages of pregnancy, a study suggests.
The study linked snoring to weight gain
An Edinburgh University team found 17 of the 100 non-pregnant females it studied snored, compared to 41 of the 100 pregnant women it looked at.
The team found their pregnant subjects' airways tended to be narrower.
The study in the European Respiratory Journal linked this with weight gain and pressure on the lungs and trachea caused by the distended abdomen.
In pregnancy the additional weight caused by the growing foetus pushes the mother's lungs and diaphragm upwards, which in turn presses on the trachea.
This is thought to lead to narrowing of the airways, the team said.
The researchers also found that women who snored tended to have neck circumferences on average one centimetre greater than fellow non-snorers.
"Fat can infiltrate the pharyngeal muscles or be deposited in the soft tissue of the neck and around the upper airways, which can increase neck size and narrow the airways," said lead researcher Professor Neil Douglas, expert in Respiratory Medicine and Sleep.
The Scottish team devised an original sound-wave method to measure their subjects' throats in a range of different positions.
This involved mapping their throats by bouncing sound waves into their mouths and looking at the shape which came back.
However the team acknowledge the clinical significance of this requires further study.
They also note that blood pressure rises among pregnancy women as their airways become narrower.
The team said as high blood pressure is linked to pre-eclampsia, the discovery adds strength to data that pregnant snorers were at greater risk of the condition which can lead to maternal and infant death if not properly monitored.
Professor Douglas said: "Some people with excessive snoring during pregnancy may have a blood pressure problem and they should mention that they are snoring very badly to their midwife or doctor."
Belinda Phipps, chief executive of the National Childbirth Trust, said it was always useful to find out further facts about pregnancy.
"There seems to be a solid association between weight gain and snoring but it is not clear if there is a risk or not."
She suggested, however, that anyone who was snoring while pregnant should not be too concerned.
"They should put this low on their list of paranoia," she added.