Fetal activity in 100 normal third trimester pregnancies.

The incidence of fetal breathing movements (FBM), fetal trunk movements (FTM), and total fetal activity (TFA) was assessed in 100 normal pregnancies between 28 weeks and term. One 30-minute recording was made from each patient between 0900 and 1700 hours. The mean incidences of FBM, FTM and TFA were respectively 37 +/- 26 (SD) per cent, 18 +/- 10 per cent, and 53 +/- 24 per cent. The mean breathing rate was 48 +/- 12 per minute, and the mean nunber of movements per 30-minute study period was 29 +/- 15. There was a slightly higher incidence of FBM postprandially, but this failed to reach statistical significance. The mean incidence of FBM was lower before 31 weeks and after 40 weeks, compared to that between 31 and 40 weeks, when the values of FBM and FTM were constant. The breathing rate was directly related to gestational age. The mean number of movements per 30-minute study period was inversely related to gestational age, but the duration of movements increased progressively towards term, so that the incidence of FTM was constant throughout the third trimester. There was only one recording of TFA below 10 per cent.