Inhibition of gonadotropin surge by a brief mid-cycle regimen of ethinyl estradiol and norethindrone: possible role in in vitro fertilization

Various methods to prevent premature luteinizing hormone (LH) surge and improve cycle control during hyperstimulation for in vitro fertilization (IVF) are standard of care. The purpose of the present study was to determine the influence of a 5-day regimen of ethinyl estradiol (EE) and norethindrone (NET) on folliculogenesis, gonadotropin surge, and ovulation. In a prospective randomized and comparative study, ten patients were assigned to two groups. A combination of 50 μg of EE and 1 mg of NET was used in groups I and II from days 6 through 10, and days 8 through 12, respectively. Blood samples and transvaginal ultrasound imaging were carried out throughout a 28-day cycle. Follicular diameter, plasma levels of LH, follicle-stimulating hormone (FSH), estradiol and progesterone, and endometrial thickness were determined. No LH surge or ovulation was detected in any patient studied. Peak estradiol concentrations were not significantly different between the groups (152.04 ± 107.1 pg/ml vs 162.1 ± 56.1 pg/ml [mean ± SD] for groups I and II, respectively). No differences were noted between the groups for serum concentrations of FSH (range: 2-9 mIU/ml) or LH (range: 2-10 mIU/ml) for any given cycle day. Mean follicular diameters were not different between groups I and II (20.5 ± 8.1 mm2 vs 20.6 ± 14.2 mm2). Ultrasound assessment of mid-cycle follicular growth revealed diameters ranging from 18.5 mm2 to 34.0 mm2. Endometrial thickness ranged from 8 to 10 mm. There was no evidence of ovulation on ultrasound examination and either persistence or gradual resolution of follicles through the luteal phase. Peak serum concentrations at mid-luteal phase were ≤ 2 ng/ml. In this pilot study, the combination of EE and NET restricted to a 5-day course beginning on day 6 or 8 permitted folliculogenesis but effectively inhibited mid-cycle LH surge and ovulation. Such regimens may have a role in IVF cycles for prevention of premature LH surges, especially as stimulation regimens evolve toward decreased gonadotropin use for stimulation and strict FSH preparations with the potential need for less complete pituitary suppression.