Ultrasonographic assessment of fetal growth: comparison between human and ovine fetus

Our purpose was to evaluate the rate of ovine fetal growth for several body parameters by serial ultrasonographic measurements and to compare them with analogous data in the human fetus.

Forty-three ewes with singleton gestations were studied. Four parameters were measured: biparietal diameter, abdominal circumference, femur length, and tibia length. Ultrasonographic examinations were performed weekly from 50 to 138 days of gestation (term 147 days). Quadratic regression analysis was used to describe each data set.

The biparietal diameter showed a significant deceleration of its growth rate. The abdominal circumference showed a linear growth pattern. Both femur and tibia revealed a significant acceleration of the growth rate.

The ovine fetal growth pattern is different from that observed in the human fetus, in which all four parameters show deceleration of the growth rate in late gestation. In comparison to the ovine, the human fetus reaches similar abdominal circumference and femur length values at term, but in a gestational period that is twice as long. In sharp contrast to abdominal circumference and femur length growth, the biparietal diameter has a similar growth rate in both species. Thus the human fetus has a slower rate of somatic growth and its greater biparietal diameter at term results from the longer gestational period.