We used real-time ultrasound to measure motility and abdominal diameter in fetal lambs at weekly intervals for 30 minutes from 55 days to term (n = 8). Fetal body movement counts/min were relatively constant between 55 and ~90 days and declined progressively thereafter, a relationship best described by piecewise linear regression with 2 elements. The break point in the regression curves averaged 91.9 ± 5.2 days. The relationship between gestational age and abdominal diameter was also best described by piecewise linear regression. The break point of 113.1 ± 3.9 days was significantly greater than the movement break point. There was a significant linear relationship between the movement and abdominal break points, with the latter occurring 21.6 ± 6.6 days later. These results suggest that both fetal motility and growth may decrease in order to lower fetal O2 demands to match the progressive decline in fetal O2 delivery with advancing gestation.