Effects of maternal exposure to constant light and maternal melatonin replacement on fetal biometry at day 18 of gestation (mean ± SEM).

LD, mothers under light-dark cycle 12∶12. LL, mothers under constant lights between 10 and 18 days of gestation. LL+Mel, Mothers under LL receiving a daily oral dose of melatonin. n, number of animals.*: Different from LD and LL+Mel (PLD组：孕鼠处于12∶12的光暗循环（Light-Dark cycle）环境中。LL组：孕鼠在妊娠第10至18天期间处于持续光照环境。LL+Mel组：孕鼠处于持续光照环境，且每日经口给予褪黑素（melatonin）。n为受试动物数量。*：与LD组及LL+Mel组存在统计学差异（P