Women who work shifts are more likely to have reduced fertility levels, new research has revealed.
Shift work also increases the chance of menstrual disruption, while night work increases the risk of miscarriage, the study found.
The annual meeting of the European Society of Human Reproduction and Embryology in London heard that previous research has linked shift work, which causes sleep deprivation and disruption to the body clock, with ill health.
But little was known about the effects of shift work on reproductive health and fertility.
Dr Linden Stocker headed a study by the University of Southampton which found links between shift patterns and fertility problems.
The study is a meta-analysis of all studies on the subject published between 1969 and January 2013 and included data on 119,345 women.
It found that those working shifts had a 33 per cent higher rate of menstrual disruption than those working regular hours, and an 80 per cent increased rate of reduced fertility.
Women who worked only nights did not have an increased risk of menstrual disruption or difficulty conceiving, but they did have a 29 per cent increased rate of miscarriage.
The investigators describe their findings as "novel," but in keeping with other studies.
"If replicated, our findings have implications for women attempting to become pregnant, as well as for their employers," Dr Stocker said.
"Whilst we have demonstrated an association between shift work and negative early reproductive outcomes, we have not proven causation.
"In humans, the long-term effects of altering circadian rhythms are inherently difficult to study. As a proxy measure, the sleep disruption demonstrated by the shift workers in our study creates short- and long-term biological disturbances.
"Shift workers adopt poor sleep hygiene, suffer sleep deprivation and develop activity levels that are out-of-sync with their body clock.
"However, if our results are confirmed by other studies, there may be implications for shift workers and their reproductive plans.
"More friendly shift patterns, with less impact on circadian rhythm, could be adopted where practical - although the optimal shift pattern required to maximise reproductive potential is yet to be established."
She said that the underlying biological disturbances involved in reproductive difficulties "are complex and not the same across all the disease processes".
"It is probable that completely different causes underlie menstrual dysfunction, miscarriage and subfertility.
"This may explain why the effects of different types of shift work are seen in some groups of women, but not others."
- DAILY MAIL