London: Women who work shifts are 80 per cent more likely to have fertility problems, a new study has warned.
UK researchers found that shift work also increases the risk of menstrual disruption, while working only night shifts increases the risk of miscarriage.
Shift work, which encourages sleep deprivation and patterns of activity outside the circadian rhythm, has been associated with a greater risk of ill health and loss of well-being in some studies.
The new study by Dr Linden Stocker from the University of Southampton, UK, indicates that working shift patterns is associated with an increased risk of menstrual disruption and subfertility.
The study is a meta-analysis of all studies on the subject published between 1969 and January 2013. It compares the impact of non-standard working schedules (including night-shift work and mixed-shifts) with that in women not working shifts.
The end-points were early reproductive outcome parameters, including menstrual dysregulation, female fertility and miscarriage rates.
The study, which included data on 119,345 women, found that those working shifts (alternating shifts, evenings and nights) had a 33 per cent higher rate of menstrual disruption than those working regular hours and an 80 per cent increased rate of subfertility.
Women who worked only nights did not have a statistically increased risk of menstrual disruption or difficulty conceiving, but they did have an increased rate of miscarriage.
This increased risk of miscarriage was not observed in women who worked nights as part of a shift pattern.
The investigators describe their findings as "novel", but in keeping with other studies (which found adverse effects in later pregnancy). "If replicated," they said, "our findings have implications for women attempting to become pregnant, as well as for their employers".
"Whilst we have demonstrated an association between shift work and negative early reproductive outcomes, we have not proven causation," Stocker said.
"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," Stocker said.
The study was presented at the annual meeting of European Society of Human Reproduction and Embryology (ESHRE) in London.