Shift work and pregnancy outcomes: a systematic review with meta-analysis of currently available epidemiological studies

Background Varying work schedules are suspected of increasing risks to pregnant women and to fetal wellbeing. In particular, maternal hormonal disturbance arising from sleep deprivation or circadian rhythm disruption might impair fetal growth or lead to complications of pregnancy. Two independent meta-analyses (from 2000 to 2007) reported a small adverse effect of shift work on the risk of preterm delivery (PTD). However, these reviews were based on few high-quality studies. Objectives To provide an updated review of the associations of shift work with PTD, low birthweight (LBW), small-for-gestational-age (SGA) infants and pre-eclampsia. Search strategy and selection criteria We conducted a systematic search of MEDLINE using combinations of keywords and MeSH terms. Data collection and analysis For each relevant paper we abstracted standard details, used to summarise design features and rate methodological quality. We calculated pooled estimates of relative risk (RR) in random-effect meta-analyses. Main results We retrieved 23 relevant studies. The pooled estimate of RR for PTD was 1.16 (95% CI 1.00-1.33, 16 studies), but when five reports of poorer methodological quality were excluded, the estimated RR decreased to 1.03 (95% CI 0.93-1.14). We also observed increased RRs for LBW (RR 1.27, 95% CI 0.93-1.74) and for SGA (RR 1.12, 95% CI 1.03-1.22), which varied little by study quality. Little evidence was found on pre-eclampsia. Conclusions These findings suggest that overall, any risk of PTD, LBW, or SGA arising from shift work in pregnancy is small.