Gyenes DL, et al. - Data collected from 305 fetuses from 279 pregnancies were examined to estimate the progression in the fetal atrioventricular interval from the first trimester to 40 weeks of pregnancy period, and also to assess functional and electrophysiological events which could impact its development. They observed an inverse relationship between heart rate and atrioventricular interval initially, then a decrease was noted before 10 weeks and then a gradual incline. Conversely, the A-wave duration linearly increased through gestation and was associated negatively with heart rate. They concluded the indication of lengthened isovolumic contraction time, which was probably affected by the development of ventricular function and afterload, is reflected in a prolonged atrioventricular interval in healthy fetuses before 10 weeks.