April 1, 2011
By Amy Norton
NEW YORK (Reuters Health) – Women who work rotating shifts may be somewhat more likely to experience shifting menstrual cycles according to a new study that raises the possibility of work schedules affecting fertility.
In a study of more than 71,000 U.S. nurses, researchers found that those working rotating shifts were more likely than other nurses to have irregular menstrual periods.
Irregular, for the purposes of the study, meant that the time between a woman’s periods usually varied by more than a week.
Women on rotating shifts were also more likely to have either very short menstrual cycles (fewer than 21 days between periods) or very long ones (40-plus days) — although few women in the study were at either of those extremes.
In general, menstrual irregularities make it harder for a woman to become pregnant. Whether shift work induces disruptions in some women’s cycles that contribute to infertility remains unknown for now.
The current findings do not actually prove that shift work, itself, disrupts women’s menstrual periods, according to lead researcher Christina C. Lawson, of the U.S. National Institute for Occupational Safety and Health.
Her team factored in a number of other things that might explain the link, however — like the women’s age, weight and exercise levels — and shift work was still connected to menstrual irregularities, Lawson told Reuters Health.
“That gives us more confidence in the association,” Lawson said, but an association does not necessarily equate to cause-and-effect.
On the other hand, there are physiological reasons to believe that rotating shifts could alter a woman’s menstrual cycle.