Objective: To evaluate whether an abnormal fetal heart rate (FHR) is associated with chromosomal abnormalities in pregnant women undergoing an invasive procedure for prenatal diagnosis, and to investigate an abnormal FHR's potential value in predicting fetal loss in chromosomally normal pregnancies after the procedure.
Methods: This was a prospective study including 867 women, all consecutive singleton pregnancies at 10-18 weeks' gestation, who underwent chorionic villus sampling (n = 371) or genetic amniocentesis (n = 496) at our institution. Fetal heart rate, expressed as beats per minute, was measured before the invasive procedure. Structural malformations detected by ultrasound were excluded.
Results: Chromosomal abnormalities were diagnosed in 25 fetuses, including 11 with trisomy 21. In ten of 25 fetuses with chromosomal abnormalities, the FHR was between the fifth and 95th percentiles established before the procedure for the chromosomally normal group with normal outcome. Using the fifth percentile as a cutoff for trisomy 21, the detection rate was 63.6%, with a specificity of 96.2% and a positive predictive value of 17.9% (one in 5.5) in our population. Moreover, in six of the ten chromosomally normal miscarriages occurring within 4 weeks after the procedure, the FHR was above the 95th percentile.
Conclusion: Although the value of a single measurement for screening purposes needs to be confirmed by further investigation, our preliminary data suggest that chromosomal anomalies, especially trisomy 21, may be suspected in fetuses with an abnormally low FHR in early pregnancy. In chromosomally normal fetuses, the detection of an abnormally high FHR in some degree may be predictive of fetal loss after the invasive procedure.