Statistically Significant Difference in the First-trimester Fetal Heart Rate between Genders?

Background: The study aims to establish the pattern of fetal heart rates in the first and second trimesters and determine whether there is a statistically significant difference in the first-trimester fetal heart rate (FHR) of males and females. Methods: This retrospective observational research is a study of FHRs measured at 11+0–13+6 wk and 18+0–23+6 wk, and ultrasound scan-diagnosed fetal sex at 18+0–23+6 wk. Singleton fetuses with nonambiguous external genitalia were recruited. The FHR was measured in B or M mode with Pulsed Wave Doppler, while ultrasound appearance of external genitalia determined the fetal sex at 18+0–23+6 wk. Student’s t-test and Chi-square test were used for data analysis, and statistical significance was set at p < 0.05. Results: A total of 2437 pregnancies meeting the study criteria were analyzed. The fetal sexes were 1398 (57.4%) males and 1039 (42.6%) females. There was no statistically significant difference in the first-trimester FHR between males and females (p = 0.74). However, females had higher mean FHR in both the first and second trimesters (First trimester: 165.4 ± 18.2 bpm vs 163.2 ± 17.1 bpm and Second trimester: 150.9 ±22.6 bpm vs 141.9 ±23.1 bpm). The FHR reduces with the increase in gestational age. Conclusion: There is no statistically significant difference in the first-trimester FHRs between sexes.