FETAL HEART-RATE IN TRISOMY-21 AND OTHER CHROMOSOMAL-ABNORMALITIES AT10-14 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 tr anslucency thickness and maternal age. In 6903 normal singleton pregna ncies the fetal heart rate decreased from a mean of 171 bpm at 10 week s of gestation to 156 bpm at 14 weeks (r = 0.413, p < 0.0001). In 85 t risomy 21 pregnancies, the mean heart rate was significantly higher th an in the normal group (mean difference 0.67 SD, 95% confidence interv al 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 Tur ner syndrome was higher than normal. There was no significant associat ion between delta fetal heart rate and delta nuchal translucency thick ness in either the normal (r = -0.018) or the trisomy 21 (r = -0.031) pregnancies. Consequently, the risk for chromosomal defects can be der ived by combining data from maternal age, fetal nuchal translucency an d 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 690 3 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 fe tal 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 translucenc y thickness and fetal heart rate.