Tachycardia Abnormal fetal cardiovascular physiology Fetal tachycardia 2024-02-04T06:29:33Z The number of beats per minute (bpm) of the fetal heart is above the upper limit of the normal for the gestational age. Fetal tachycardia is thus defined as a heart rate greater than 160-180 bpm. In the first trimester of pregnancy, the fetal heart rate (FHR)increases from 125 beats per minute (bpm) at 6 weeks to about175 bpm at 9 weeks, followed by a gradual decrease to about160 bpm at 14 weeks, noted in fetuses conceived by assisted reproductive procedures.