Are the behavioural states of the newborn comparable to those of the fetus?

Comparisons were made between ultrasound behavioural recordings of 18 healthy term fetuses and recordings of the same variables of the same individuals at 3 to 5 days postnatally. Statistical comparison of the frequency of eye movements, limb and body movements revealed that the fetal states 1F and 2F were comparable to quiet sleep (S1), and rapid eye movement (REM) sleep (S2), respectively in the newborn. Comparisons between the fetal states and wakefulness were less clear-cut. The heart rate in each of the three states in the fetus was about 20 beats per min higher than in the corresponding postnatal state, although the patterns were similar. States 1F and 2F accounted for a higher percentage of the fetal observations (86%) than states S1 and S2 in the neonatal observations (64%), but the ratio of the different types of sleep was similar in both recordings (30% quiet sleep to 70% REM sleep). State S3 (quiet awake) always and only occurred in the postnatal observations in association with feeding. No comparable behaviour occurred during the prenatal observations (2050 min in 18 fetuses). Numerically the movements observed in S5 (crying) were not significantly different from 2F, however qualitatively there were marked differences, and also S5 was characterized by a heart rate pattern quite unlike anything observed prenatally (often with a rate in excess of 200 beats per min). We postulate that S3 and S5 are postnatal behavioural adaptations to extrauterine existence.