Normal patterns of fetal activity in the third trimester.

The incidence and frequency of fetal respiratory movements (FRM) and fetal trunk movements (FTM) were measured in 21 normal pregnancies between 28 and 39 weeks gestation. Fetal activity was assessed with a real-time ultrasound scanner and all observed movements were punched directly onto computer tape. Recordings were made for one hour in three over a 24 hour period, providing a total of 168 hours for analysis. The overall mean percentage incidence of FRM was 31 per cent at a mean breathing rate of 43 breaths/minute. The mean percentage incidence of FRM during the day (0800-1759 hours) was 37 per cent. The overall mean percentage incidence of FTM was 18 per cent with a mean of 29 moves per 30 minute observation period. The mean percentage incidence of FTM during the day (0800-1759 hours) was 16 per cent. There was a well-defined circadian variation in fetal activity with FRM peaking between 1900 and 2200 hours, and FTM between 2200 and 0100 hours. There was considerable variation in the amount of FRM and FTM recorded from hour to hour. Total fetal activity rarely fell below 10 per cent in any one recording period and this measurement may be a more useful clinical test of fetal well-being than FRM or FTM alone.