Although a large number of studies show that photo-period disruption potentially affects hormone secretion in mammals, information about the effects of
circadian photo-period disruption during pregnancy on fetal blood reproductive hormone levels is scarce. This study used ewes and their fetuses to determine the
effects of circadian photo-period disruption (deprivation of darkness) on follicle-stimulating hormone, luteinizing hormone, estradiol, and progesterone in
maternal and fetal circulation at late gestation. Pregnant ewes (gestational age: 135 ± 3 days) were randomly placed into control and dark deprivation groups.
The control (N = 5) and dark deprivation (N = 5) groups were exposed to a fixed 12 h light/12 h dark cycle and a 24 h constant light cycle, respectively, for 2
days. Dark deprivation up-regulated follicle-stimulating hormone and estradiol levels and down-regulated progesterone levels in both maternal and fetal
circulation, and up-regulated luteinizing hormone levels in fetal but not maternal circulation. These results provide new information about how circadian
photo-period disruption during pregnancy could alter the release of certain reproductive hormones into fetal blood, which may influence the development of fetal
organs in utero, as well as long-term health.