MTNR1B and sleep disorder: We examined the placenta of mothers with sleep disorder, occurring extend from the third trimester of pregnancy to postpartum, and showed that NR3C2 methylation decreased and MTNR1B methylation increased, which supports the hypothesis that maternal sleep disorders in the third trimester of pregnancy could increase maternal postpartum sleep disorder by changing placental NR3C2 and MNTR1B methylation levels.