Evaluation of the bioeffects of prenatal ultrasound exposure in the cynomolgus macaque (Macaca fascicularis): III. Developmental and hematologic studies.

The multiple applications of diagnostic ultrasound in obstetrics have resulted in a continued rise in the prenatal population exposed each year. Although human epidemiologic and experimental studies with various animal models have not consistently documented any significant, reproducible findings related to clinically relevant exposures, technologic changes in scanning equipment and gaps in our knowledge regarding the interaction(s) of ultrasound with tissues emphasize the need to pursue safety issues. Studies with nonhuman primates have provided information on the potential for pre and postnatal effects on offspring exposed repeatedly during gestation (ATL MK 600, 7.5 MHz, ISPTA = 27 mW/cm2; ISPPA = 85 W/cm2; Estimated power = 12 mW--scanned for 10 min 5 times weekly gestational day [GD] 20-35; 3 times weekly GD 36-60; once weekly for 20 min GD 60-150). These studies have indicated transient effects on body weight, white blood cell counts (WBCs), and muscle tone postnatally. In an effort to confirm these findings and focus on hematologic changes, a second series of studies was initiated using the same exposure conditions (N = 22; 11 exposed, 11 sham controls). Data derived from both studies were combined and confirmed transient reductions in body weights for infants up through 4 months of age (P < or = 0.03); no statistically significant differences in muscle tone were noted. Similar to the original findings, WBCs were transiently reduced on days 3 (P < or = 0.02) and 21 (P < or = 0.05); prenatal sampling indicated a significant difference between the groups on GD 140 (P < or = 0.04). No direct effects were evident in bone marrow aspirates collected on postnatal days 3, 9, and 21 +/- 1. Although animals were able to compensate for these observed changes and remained unaffected by their occurrence, additional studies will be required to further our understanding of this phenomenon.