Smiles in the fetal period.

Five-hundred-sixty-eight fetuses were observed at a clinic by using four-dimensional ultrasonography, and 31 fetuses who showed smiles were selected. The range of conceptional age was from 156 days to 214 days. The participants exhibited 51 smiles in 62 min of recording. The average duration of smiles was 3.21s (SD = 1.98). This must be the first study which collected fetal smiles intensively. The age effect on the frequency and duration of fetal smiles is not examined in this study. In comparison with previous studies, the average duration of fetal smiles and that of spontaneous smiles in preterm neonates (3.28s; Kawakami et al., 2008) were not significantly different, but they were significantly longer than that of spontaneous smiles in full-term neonates (1.97s; Kawakami et al., 2006). The fact that fetuses show a lot of smiles makes us reconsider the meanings of spontaneous smiles; fetal smiles must not result from social effects.