First trimester embryonic/fetal heart rate in normal pregnant women

Objective: To establish reference ranges for first trimester embryonic/fetal heart rate in normal pregnant women. Materials and methods: This was a cross-sectional study. We performed ultrasonogram in 319 normal pregnant women, gestation age between 6⁺⁰ and 14⁺⁶ weeks and measured embryonic/fetal heart rates using M-mode. The embryonic/fetal heart rates were analyzed according to gestational ages (GA). Results: Data of 319 pregnancies were analyzed and the outcome revealed the mean of fetal heart rate according to gestational age. The mean embryonic heart rates during the 6th–7th week of gestation are lower when compared with the other gestational ages. At the 8th week of gestation, the embryonic heart rate is maximum. Then the embryonic/fetal heart rate gradually decreased to 161 beats/min at the 14th week of gestation. The regression equation for embryonic/fetal heart rate (beat/min) [y] according to GA (day) [x] was y = −53.124 + 6.1333x + (−0.0407)x ² (r ² = 0.525; P < 0.001). Conclusion: Embryonic/fetal heart rates during the 6⁺⁰ and 14⁺⁶ week of gestation are related to GA. Our reference ranges may be useful for further studies such as for prediction of adverse pregnancy outcome in threatened abortion.