Simulated shift work disrupts maternal circadian rhythms and metabolism, and increases gestation length in sheep

Key Points

Shift work impairs metabolic health, but its effects during pregnancy are not well understood We evaluated effects of a simulated shift work protocol for 1/3, 2/3 or all of pregnancy on maternal and pregnancy outcomes in sheep. Simulated shift work changed the timing of activity, disrupted hormonal and cellular rhythms, and impaired maternal glucose tolerance during early pregnancy. Gestation length was increased in twin pregnancies while singleton lambs were lighter at a given gestational age if mothers were subjected to shift work conditions in the first 1/3 of pregnancy. Exposure to rotating night and day shifts, even if only in early pregnancy, may adversely affect maternal metabolic and pregnancy outcomes.

Abstract

Shift workers are at increased risk of developing type 2 diabetes and obesity, however the impact during pregnancy on maternal metabolism is unknown. Using a large animal model, we assessed the impact of simulated shift work (SSW) exposure during pregnancy on maternal circadian rhythms, glucose tolerance and pregnancy outcomes. Following mating, ewes were randomly allocated to a control photoperiod (CON 12 h light, 12 h dark) or to SSW, where the timing of light exposure and food presentation was reversed twice each week for 1/3, 2/3 or all of pregnancy. Maternal behaviour followed SSW cycles with increased activity during light exposure and feeding. Melatonin rhythms resynchronised within 2 days of the photoperiod shift, whereas peripheral circadian rhythms were arrhythmic. SSW impaired glucose tolerance (+29%, P = 0.019) and increased glucose stimulated insulin secretion (+32%, P = 0.018) in ewes with a singleton fetus in early but not late gestation. SSW exposure did not alter rates of miscarriage or stillbirth, but extended gestation length in twin pregnancies (+2.4 days, P = 0.032). Relative to gestational age, birth weight was lower in singleton progeny of SSW than CON ewes (‐476 g, P = 0.016). These results have implications for the large number of women currently engaged in shift work, and further studies are required to determine progeny health impacts.

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