Effects of a preovulatory single low dose of mifepristone on ovarian
function
J.G. van der Stege (1), E.H. Pahl-van Beest (2), R.J.C.M. Beerthuizen
(3), H.W. van Lunsen (4), P.C. Scholten (5), D.H. Bogchelman (2)
Department of Obstetrics and Gynaecology, Martini Hospital Groningen (1);
Department of Obstetrics and Gynaecology, University Hospital Groningen (2);
Dutch Foundation for Contraception (3); Department of Sexology &
Psychosomatic Obstetrics and Gynaecology, Academic Medical Centre, University of
Amsterdam (4); Department of Obstetrics and Gynaecology, Diakonessenhuis,
Utrecht, The Netherlands (5)
Introduction: Mifepristone has been used as an effective drug for
emergency contraception when administered within 120 h after unprotected
intercourse. A comparison of different doses of mifepristone showed that a dose
of 10 mg is as effective as a dose of 600 mg in preventing pregnancy, while
causing less disturbance of the menstrual cycle. The effect of mifepristone on
the menstrual cycle is dependent on the adjusted dose and the timing of the
treatment. Previous studies have shown that follicular phase administration of
high doses of mifepristone inhibits LH surge and delays folliculogenesis. The
purpose of this study is to examine whether administration of mifepristone in a
single low dose during the preovulatory period has similar effects on ovulation.
Material and methods: Healthy women with regular menstrual cycles were
studied during two consecutive menstrual cycles. Either mifepristone or placebo
was given in a randomized double blind order when the leading follicle reached a
diameter between 15–17 mm. Daily ultrasound and serum hormone measurements
were obtained until follicular collapse. Statistical analysis was performed
using Wilcoxon signed-rank test.
Results: Eight women entered the study while one woman was excluded
afterwards from analysis because her LH surge had already appeared on the day of
treatment. Mifepristone caused a three-day delay in follicular collapse,
occurring on day 16 in control cycles and on day 19 in mifepristone treatment
cycles (p=0.02). The LH surge was delayed from day 14 to day 17 (p=0.01). The
median cycle length was 26 days in control cycles and 30 days in mifepristone
treatment cycles (p=0.03). Progesterone measurement 7 days after follicular
collapse did not differ significantly between both cycles.
Conclusions: A single dose of 10 mg mifepristone administered during
the preovulatory phase of the cycle delays the LH surge and postpones ovulation.
