Fetal movements during late gestation in the pig: a longitudinal ultrasonographic study

Repeated ultrasonographic observation of fetal movements was used to distinguish movement patterns and to investigate the rate of occurrence and temporal organisation of these patterns (rest-activity cycles) during the last three weeks of gestation in the pig. By means of transabdominal ultrasonography with a 3.5MHz linear array transducer, motility in ten different fetuses (one per sow) was studied. Six (median; range 4-6) 1h recordings were made per fetus at 3-5 day intervals. Fifty-five 1h recordings were available for analysis. The occurrence of fetal general movements (GM), isolated head (HM), forelimb movements (LM), and rotations (ROT) was analysed from video tapes. For each movement pattern, the trend in occurrence over time was assessed by multilevel analysis. The temporal association between different movement patterns was studied by calculation of the kappa value. ROT occurred very infrequently and showed no particular trend over time. GM, HM, and LM showed a significant decreasing trend towards parturition (P<0.01). Total fetal activity (i.e., the sum of the four movement incidences) declined from an average of 25% of recording time to 9% over the last three weeks of pregnancy. Periods of fetal quiescence gradually increased with progressing gestation (P<0.05). There was no evidence of concordant association between the periods of rest and activity of GM, HM, and LM or of improved temporal linkage between these movement patterns with time. Fetal bodily activity decreases towards parturition mainly due to prolonged periods of rest. Fetal movement patterns show rest-activity cycles, but each pattern appears to cycle independently from the other throughout late gestation. The present results of spontaneous fetal movements in the pig provide reference data for future studies of fetal activity under different zoo technical conditions or pharmacological interventions.