Fetal Sleep

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International Journal of Childbirth Education

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This paper reviews available evidence on fetal and maternal sleep states during pregnancy. While the mother spends the bulk of her sleep time during pregnancy in NREM (non REM) Stage N2 (light) sleep, the developing baby spends the bulk of its sleep time in REM. Fetal REM is synchronized with maternal wake-rest activity schedules and is tightly coupled to respiratory physiology. Fetal REM exhibits hormonal and sensory signaling functions as well. The absence of sufficient fetal REM activity is associated with fetal distress and may be interpreted as a danger signal by the pregnant mother. It is suggested that maternal N2 NREM light sleep allows the mother to quickly awaken and respond to any danger signals received from internal or external sources. Near term NREM Stage N3 (slow wave activity) helps initiate birth contractions. At birth fetal REM is maximal and declines rapidly in the neonate.