Establishing whether miscarriages result from fetal aneuploidy or other factors is important for treating recurrent pregnancy loss. We examined the relationship between fetal heart rate (FHR) before miscarriage in the early first trimester and fetal karyotype, analyzing 223 pregnant women with recurrent pregnancy loss. Among the pregnancies, 110 resulted in live births regarded as normal karyotype (the Norm-group). The other 113 pregnancies ended in miscarriage, and we categorized them into groups based on fetal karyotype, determined by chorionic villus sampling: the Misc-NK (normal karyotype) group, n=35 euploid cases; the Misc-CA1 (chromosomal abnormality) group, n=18 cases of aneuploidy with trisomies 13/18/21, Turner’s syndrome, or Klinefelter’s syndrome; and the Misc-CA2 subgroup, n=60 cases of other aneuploidies excluding those in the Misc-CA1 group. We compared the groups’ regression line slopes and intercepts for FHR by an analysis of covariance. The FHRs of the Norm, Misc-NK and Misc-CA1 groups increased from 36 to 49 days after fertilization, but did not significantly differ across these groups. The Misc-CA2 group’s FHR did not increase and significantly differed from the other three groups (p<0.01). These results suggest that the absence of an increase in FHR in early pregnancy may indicate the presence of chromosomal abnormalities causing miscarriage.