Feasibility of continuous recording of fetal heart rate in the near term bovine fetus by means of transabdominal Doppler.

A transabdominal Doppler technique for the recording of fetal heart rate (FHR) was investigated in the bovine fetus. During the last 2 weeks of gestation recordings were made once or twice per week in eight cows by placing a 1.5 MHz Doppler transducer on the right ventral abdominal wall. Continuous FHR recordings with a duration of more than 30 min were obtained in 29 of the 35 sessions. Major displacements of the fetus were the main cause of recording failure. The overall mean baseline FHR was 105 +/- 1.5 bpm with a range of 90 to 125 bpm. The mean bandwidth of the baseline FHR was 10.8 +/- 0.7 bpm with a range of < 5 to 20 bpm. Periods with different bandwidths alternated. The alternation of bovine FHR patterns pointed to the existence of different fetal behavioural states. The mean number of accelerations of FHR was 7.1 +/- 1.0 per hour. Many of the accelerations coincided with visible or perceptible fetal body movements. Decelerations of FHR occurred less frequently (range 0 to 4 per h). A period of tachycardia accompanied by an increased number of fetal movements occurred in 3 of the 29 FHR recordings. This non-invasive technique appears to be suitable to study FHR patterns during gestation and to investigate the presence and characteristics of behavioural states in the bovine fetus. It also provides the possibility to study effects on the fetus of drugs administered to the dam.