Objective: To compare the outcome of natural with clomiphene citrate (CC)-stimulated cycles in IVF.
Design: Prospective, randomized study.
Setting: Tertiary referral center for assisted conception.
Subjects: Thirty patients randomized to receive either no treatment (n = 14) or CC, 100 mg, from days 2 to 6 (n = 16).
Interventions: Daily ultrasound (US) scan and measurements of serum LH and E2. Ovarian morphology was assessed on baseline US scan. Human chorionic gonadotrophin was administered when the mean diameter of the dominant follicle reached 17 mm. Transvaginal US-directed oocyte recovery was performed 35 hours later.
Main outcome measures: The number of patients reaching oocyte recovery; numbers of oocytes collected, fertilized and embryos transferred; and clinical pregnancy and multiple pregnancy rates (PRs) were recorded.
Results: Ten cycles in the natural cycle group were abandoned before oocyte recovery compared with none in the CC group. There were significantly more follicles > 14 mm (2.4 +/- 0.3 [SE] compared with 0.9 +/- 0.2) and higher peak levels of E2 (375 +/- 67 pg/mL (1,378 +/- 247 pmol/L) compared with 204 +/- 17 pg/mL (748 +/- 61 pmol/L)) in those receiving CC compared with those receiving no drug. All 16 patients treated with CC had oocyte retrieval (mean, 1.8 +/- 0.3 oocytes) compared with only 4 in the natural cycle group (1 oocyte each). The oocyte recovery rate was 95%. Two patients conceived in the CC group (PR per ET, 18%) compared with none in the natural cycle group. Patients with polycystic ovaries developed more large follicles than those with normal ovaries. No patient developed ovarian hyperstimulation syndrome.
Conclusions: Patients undergoing natural cycle IVF are more likely to have abandoned cycles, produce fewer follicles and oocytes, and are less likely to reach ET than patients treated with CC alone. Clomiphene citrate should be considered for use in the context of a conventionally organised IVF-ET program if a mild degree of ovarian stimulation is desired.