The diurnal rhythm in fetal heart rate in a twin pregnancy with discordant anencephaly: comparison with three normal twin pregnancies.

In a discordant anencephalic twin the hypothesis was tested that the fetal brain is necessary for the expression of a diurnal rhythm in fetal heart rate. Fetal heart rate recordings were made over a 24 h period in a discordant anencephalic twin pregnancy and in three normal twin pregnancies. Cosinor analysis was used to assess rhythmicity in fetal heart rate and maternal heart rate or activity. Correlations between maternal and fetal rhythms were calculated. A significant diurnal rhythm was found for the fetuses of the control twins, but in neither of the fetuses of the discordant anencephalic twin pregnancy. The maternal rhythm was 1-2 h in advance of the heart rate rhythms in all fetuses except the anencephalic one, whose heart rate did not show any correlation with the maternal diurnal rhythm. We conclude that the fetal brain contributes to the generation of the diurnal rhythm in fetal heart rate and synchronization of maternal-fetal rhythms.