Determination of in utero fetal rat heart rate by ultrasound

A technique for in utero determination of rat fetal heart rat in conscious and anesthetized animals is described. Fetal heart rate was analyzed using echocardiography by recording two-dimensional ultrasound images along with the derived M-mode tracing. This method allows for the simultaneous and sequential analysis of both maternal and fetal heart rate after exposure to therapeutic or environmental agents. When compared to other techniques, this noninvasive approach can clearly yield a more accurate assessment of drug effects on the fetal cardiovascular system. The method eliminates the influence of surgical manipulation on cardiac activity. More importantly, this approach can avoid the use of cardiodepressant anesthetic drugs and their potential interaction with agents under investigation. This method is thereby more sensitive and specific for determining the effects of compounds under study than previously described techniques. To illustrate this system, fetal heart rates are compared after maternal propranolol administration in conscious and anesthetized animals.