460 In a previous study on diurnal rhythms in normal preg- nancy we quantified rhythms in various computed fetal heart rate (FHR) parameters. We concluded that the di- urnal rhythm in basal FHR, which was present in 73% of the fetuses and was correlated with the maternal heart rate rhythm, is driven by the mother through an un- known mechanism. 1 It has been postulated by others that the diurnal variation in maternal cortisol concentration controls fetal rhythms. 2 In 9 pregnancies with intrauter- ine growth restriction (IUGR) we tested this hypothesis by comparing maternal heart rate and FHR rhythms be- fore and after betamethasone treatment, which com- pletely abolishes the diurnal rhythm in maternal cortisol concentration. Patients and methods From a study group of 26 pregnancies complicated by IUGR 9 patients treated with betamethasone were se- lected for this study. Betamethasone was given intramus- cularly in two doses of 14 mg 24 hours apart. After in- formed consent we made two 24-hour FHR recordings (M1350A; Hewlett-Packard, Boeblingen, Germany). The first recording was made before the first injection of be- tamethasone, and the second recording was started 1 day after the second dose. In 2 cases we measured plasma cor- tisol concentrations at 3-hour intervals during both 24- hour FHR recordings. Maternal heart rate was measured simultaneously with FHR (Polar Electro OY , Kempele, Finland). FHR parameters for analysis were as follows: basal FHR, acceleration count, and short-term variability. The methods for analysis of FHR parameters and diurnal rhythms have been described in a previous article. 1 A paired t test was used to compare the chronobiometric outcome parameters between the recordings made be- fore and after betamethasone treatment. Results Plasma cortisol concentration showed a significant di- urnal rhythm before betamethasone treatment. After treatment, plasma cortisol levels were 10- to 20-fold lower (around 0.05 μmol/ L) and did not show any rhythmicity. Six fetuses in the study group showed a significant rhythm in basal FHR both before and after betametha- sone administration. One fetus showed a significant rhythm in basal FHR before but not after betamethasone therapy. In another fetus the opposite pattern was seen. The prevalence of a diurnal rhythm in basal FHR of 78% (7/ 9) both before and after betamethasone therapy was comparable to the 73% found in 26 normal pregnancies 1 ( P = .8 by χ 2 test) and the 88% found in all 26 pregnan- cies complicated by IUGR ( P = .5). The prevalences of di- urnal rhythm in short-term variability and acceleration count were 11% (1/ 9) before and 44% (4/ 9) after be- tamethasone therapy ( P = .14). None of the fetuses showed a rhythm in acceleration count before be- tamethasone administration, whereas 3 fetuses (33%) showed a significant rhythm in acceleration count after therapy ( P = .07) . These prevalences of diurnal rhythms in short-term variability and acceleration count did not significantly differ from those in all 26 pregnancies com- plicated by IUGR or those in 26 normal pregnancies. In all women monitored a significant rhythm in maternal heart rate was present both before and after betametha- sone administration and was correlated with the rhythm From the Department of Obstetrics and Gynaecology, Academic Medical Center, University of Amsterdam, a and The Netherlands Institute for Brain Research. b Received for publication August 10, 1999; revised December 22, 1999; accepted January 24, 2000. Reprint requests: Simone Lunshof, MD, Academic Medical Center, Uni- versity of Amsterdam, Department of Obstetrics and Gynaecology, PO Box 22700, 1100 DE Amsterdam, The Netherlands. Copyright © 2000 by Mosby, Inc. 0002-9378/2000 $12.00 + 0 6/ 1/ 105965 doi:10.1067/mob.2000.105965 Lack of relationship between diurnal rhythms in fetal heart rate and maternal cortisol concentration S. Lunshof, MD, PhD, a E.J.W. van Someren, PhD, b G. Kortes-van Hoffen, b H. Wolf, MD, PhD, a and K. Boer, MD, PhD a Amsterdam, The Netherlands In 9 pregnancies complicated by intrauterine growth restriction, 24-hour fetal heart rate recordings were made before and after betamethasone treatment to study the influence of cortisol on diurnal fetal heart rate rhythms. Maternal and fetal rhythms were correlated and did not change after betamethasone administration. We conclude that diurnal fetal heart rate rhythms are synchronized by the mother through a mechanism other than adrenal control. (Am J Obstet Gynecol 2000;183:460-1.) Key words: Betamethasone, cortisol, diurnal rhythms, fetal heart rate, intrauterine growth restriction