We read with interest the recent paper by Lundberg et a1 [ 19821 which supported once again the safety of in vivo diagnostic ultrasound. It has confirmed our results obtained by a similar experimental setup [Zheng et al, 19811. We believe that we were the first to report on the mutagenic potential of in vivo diagnostic ultrasound, and on the use of cultured amniocytes for this purpose. We had obtained our control samples of amniotic fluids from pregnant women undergoing therapeutic abortions (the fluid being withdrawn prior to intramniotic instillation of prostaglandin); thus, it was interesting to note that Lundberg et a1 had obtained their control samples from a practising physician who does not use ultrasound before performing amniocentesis! In our study, the amniotic fluids for the experimental and the control group were obtained during the second trimester.
We had the same concerns as Lundborg et a1 [ 19821 regarding the validity of the study and were also unhable to control exposure doses. Lundberg et al used the "flask-method'' for culture amniocytes. This method takes much longer (14-2 1 days after initiation) for sufficient cell growth before harvest than the "in situ" method of amniocyte culture used by us (usually 9-12 days after initiation). If there exist any long-term effects of in vivo diagnostic ultrasound which diminish over time, the use of a shorter culture period would have the advantage of enhancing demonstration of increased SCE rates in cultured amniocytes. The results of our study were in agreement with those obtained by Lundberg et al, supporting the conclusion that diagnostic ultrasound probably is a safe, noninvasive obstetrical procedure.