A new study suggests that working shift patterns is associated with an increased risk of menstrual disruption and subfertility in women.
The study, by Dr Linden Stocker from the University of Southampton, UK, 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 percent higher rate of menstrual disruption than those working regular hours (odds ratio 1.22, statistically significant) and an 80 percent increased rate of subfertility (OR 1.80, statistically significant).
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 (OR 1.29), although this increased risk of miscarriage was not observed in women who worked nights as part of a shift pattern.
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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".