EFFECTS OF TOCOLYTICS ON THE FETAL HEART

Objective: Tn order to determine if tocolytic agents affect fetal vent ricular function, we used the combined ventricular shortening fraction , an echocardiographic index of fetal cardiac function to evaluate fet uses whose mothers were being treated for preterm labor. Study design: A group of 30 patients diagnosed with preterm labor and eligible for tocolytic therapy were the subjects of this prospective non-randomized cohort study. Sixteen patients were treated initially with subcutaneo us terbutaline, five with intravenous ritodrine, and nine with intrave nous magnesium sulfate. All were later maintained on oral therapy with either terbutaline or ritodrine. Each fetus acted as its own control. Each was studied before treatment, while on a clinically therapeutic intravenous or subcutaneous regimen, during oral therapy, and after bi rth. The in utero evaluations included a biophysical profile, umbilica l artery Doppler waveform study, and an M-mode tracing of ventricular wall motion generated from a four-chamber view of the heart to assess the end diastolic and the end systolic dimensions. The combined ventri cular shortening fraction was then calculated as (end diastolic - end systolic)/end diastolic x 100%. Multiple analysis of variance was used to compare means over time for each variable. Means between groups we re compared using the two-tailed Student's t test; P = 0.05 was utiliz ed. Results: No significant change was noted in the mean combined vent ricular shortening fraction of fetuses who had been exposed to tocolyt ic agents, all of whom had normal studies. The mean combined ventricul ar shortening fraction pretreatment was 34.8%, as compared with 33.9% in patients treated with beta-mimetics. Those treated with MgSO4 had a n improved mean combined ventricular shortening fraction of 37.9%. Thi s change was not statistically significant. Doppler and biophysical pr ofiles were normal, and preterm labor was successfully arrested in all cases. Conclusion: In this small pilot study short ten treatment with commonly utilized tocolytic agents did not appear to affect fetal ven tricular function.