Circadian rhythm of fetal movements.

Intra-uterine fetal movements indicate the wellbeing of the fetus and can be used in the detection of chronic fetal asphyxia. The daily variations in fetal activity follow an irregular pattern, though showing a peak of activity in the evening. The pattern of nocturnal activity is not known. In this study, fetal movements were monitored by maternal subjective recordings in 116 women with a normal pregnancy. In gestational weeks 31-40, fetal movements were recorded intermittently for at least 3 hours, both in the daytime and at night. In the daytime, fetal activity was moderate. A maximum occurred in the evening between 9 and 10 p.m. At night there was a period of minimum activity between 1 and 5 a.m. A minor peak in fetal activity was seen between 7 and 8 a.m. The frequency of fetal movements followed a pattern of a circadian rhythm, which was influenced by exogenous factors.