Fetal heart rate in chromosomally abnormal fetuses

Objectives To determine the effects of chromosomal defects on fetal heart r ate at 10-14 weeks of gestation. Methods Fetal heart rate at 10-14 weeks of gestation in 1061 chromosomally abnormal fetuses was compared to that from 25 000 normal pregnancies. The c hromosomally abnormal group included 554 cases of trisomy 21, 219 cases of trisomy 18, 95 of trisomy 13, 50 of triploidy, 115 of Turner syndrome and 2 8 of sex chromosome abnormalities other than Turner syndrome. Results In the normal group, fetal heart rate decreased from a mean value o f 170 beats per minute (bpm) at 35 mm of crown-rump length to 155 bpm at 84 mm crown-rump length. In trisomy 21, trisomy 13 and Turner syndrome fetal heart rate was significantly higher in trisomy 18 and triploidy the heart r ate was lower and in other sex chromosome defects it was not significantly different from normal. Fecal heart rate was above the 95th centile of the n ormal range in 10%, 67% and 52% of fetuses with trisomy 21, trisomy 13 and Turner syndrome, respectively. The fetal heart rate was below the 5th centi le in 30% of fetuses with triploidy and 19% of those with trisomy 28. Conclusions Trisomy 21, trisomy 13 and Turner syndrome are associated with fetal tachycardia, whereas in trisomy 18 and triploidy there is fetal brady cardia. Inclusion of fetal heart rate in a first-trimester screening progra m for trisomy 21 by a combination of maternal age and fetal nuchal transluc ency thickness is unlikely to provide useful improvement in sensitivity.