Fetal heart rate in early pregnancy and chromosomal disorders

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Abstract
Objective To investigate normal fetal heart rate in early pregnancy and assess the hypothesis that abnormal fetal heart rate is associated with fetal chromosomal abnormalities. Design Prospective descriptive cross‐sectional study. Setting Antenatal clinic associated to the University Clinic of Obstetrics, University Hospital Groningen, The Netherlands. Subjects 424 pregnant women who attended for prenatal counselling. Interventions Measurements of fetal heart rate from 6–16 weeks gestation, cross‐sectional study. Main outcome measures Fetal heart rate expressed as beats/min. Results Karyotyping showed a normal chromosomal pattern in 414 fetuses. The median fetal heart rate increased from 138 beats/min at 6 weeks to 177 beats/min at 9 weeks, thereafter, fetal heart rate gradually decreased to 150 beats/min at 16 weeks. Karyotyping showed 10 abnormalities: five trisomies 21, three trisomies 18, and two mosaic patterns in chorionic villi. Fetal heart rate of the trisomic fetuses was distributed around the median with that of all Down's syndrome fetuses within the normal range. In one fetus with trisomy 18, the heart rate exceeded the 90th centile, in another it fell under the 10th centile. The two fetuses with a mosaic pattern in chorionic villi had heart rates outside the normal range. Conclusion Fetal heart rate in chromosomally abnormal fetuses in early pregnancy do not appear to be consistently different from that in normal fetuses. The use of a single measurement of fetal heart rate is not valuable for screening purposes. Chromosomal mosaicism in chorionic villi may be associated with abnormal fetal heart rate.

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