EARLY ULTRASONOGRAPHIC DETECTION OF FETAL GROWTH-RETARDATION IN AN OVINE MODEL OF PLACENTAL INSUFFICIENCY

OBJECTIVE: Our aims were as follows: (1) to determine whether fetal gr owth retardation can be detected noninvasively with ultrasonography in ewes and (2) to establish the time interval between exposure of ewes to environmental stress that causes growth retardation (heat stress) a nd detection of growth lag for specific fetal body measurements. STUDY DESIGN: Four ewes were exposed to heat stress for 80 days starting at 35 days' gestation. (The duration of pregnancy in sheep is 147 days.) Serial ultrasonographic measurements of fetal biparietal diameter, ab dominal circumference, and femur and tibia lengths were obtained begin ning at 50 days' gestation. Growth curves were calculated for each par ameter and compared with growth curves obtained from 43 normal fetuses . RESULTS: Biparietal diameter measurements deviated significantly fro m normal starting at 90 days' gestation (p < 0.05). Abdominal circumfe rence diverged at 70 days' gestation (p < 0.05), and both femur and ti bia length diverged at 80 days (p < 0.05). The regression lines showed significant differences for all the parameters in both slope (p < 0.0 1) and intercept (p < 0.01). CONCLUSIONS: Fetal growth retardation can be detected noninvasively by ultrasonography after approximately 5 we eks of exposure to heat stress. Fetal growth continues throughout gest ation but at a slower rate than normal and according to a pattern simi lar to that observed in asymmetrically growth-retarded human fetuses. Early detection of stunted fetal growth in an animal model is importan t for testing intervention strategies in the treatment of fetal growth retardation.