Fetal heart rate in trisomy 21 and other chromosomal abnormalities at 10-14 weeks of gestation

Fetal heart rate was measured routinely as part of a prospective study examining the efficacy of screening for trisomy 21 by fetal nuchal translucency thickness and maternal age. In 6903 normal singleton pregnancies the fetal heart rate decreased from a mean of 171 bpm at 10 weeks of gestation to 156 bpm at 14 weeks (r = 0.413, p < 0.0001). In 85 trisomy 21 pregnancies, the mean heart rate was significantly higher than in the normal group (mean difference 0.67 SD, 95% confidence interval 0.42-0.92, t = 5.3, p < 0.001). The fetal heart rate in trisomy 18 and triploid fetuses was significantly lower and in trisomy 13 and Turner syndrome was higher than normal. There was no significant association between delta fetal heart rate and delta nuchal translucency thickness in either the normal (r = -0.018) or the trisomy 21 (r = -0.031) pregnancies. Consequently, the risk for chromosomal defects can be derived by combining data from maternal age, fetal nuchal translucency and fetal heart rate. The effectiveness of screening by this method was examined in a self-selected population with completed pregnancies that had undergone first-trimester scanning. This population contained 6903 normal and 29 trisomy 21 fetuses. For a false-positive rate of about 5%, the sensitivity for trisomy 21 was 48% by maternal age, 26% by fetal heart rate, 72% by nuchal translucency thickness, 59% by maternal age and fetal heart rate, 76% by maternal age and nuchal translucency thickness and 83% by a combination of maternal age, nuchal translucency thickness and fetal heart rate.