(HealthDay News) – Shift work is associated with increased rates of menstrual disruption, subfertility, and miscarriage, according to research presented at the annual meeting of the European Society of Human Reproduction and Embryology, held from July 7–10 in London.

Linden J. Stocker, from the University of Southampton in the United Kingdom, and colleagues conducted a meta-analysis of studies to examine the impact of non-standard working schedules vs. normal daytime work patterns on reproductive outcome parameters. Data from 16 studies, reporting on 121,929 women, were included in analyses.

The researchers found that women working mixed shift patterns (evening, and alternating or changing shifts, including nights) had significantly increased rates of menstrual irregularity (odds ratio, 1.33) and subfertility as measured by an increased time-to-pregnancy (odds ratio, 1.12), compared with those who worked days. For women who worked only nights, the risk of menstrual disruption or difficulty conceiving was not significantly increased, but the rate of miscarriage was increased significantly (odds ratio, 1.33). Women who worked nights as part of a mixed shift pattern did not have a significantly increased rate of miscarriage.

“Whilst we have demonstrated an association between shift work and negative early reproductive outcomes, we have not proven causation,” Stocker said in a statement. “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.”

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