Acute effects of metformin therapy include improvement of insulin resistance and ovarian morphology.

Objective: To evaluate the acute effects of metformin therapy on biochemical markers and polycystic ovarian morphology among insulin-resistant (IR) and noninsulin-resistant (NIR) patients with polycystic ovary syndrome (PCOS).

Design: Prospective interventional study.

Setting: Reproductive endocrinology clinic in a university hospital.

Patient(s): Five IR and five NIR patients with PCOS. The mean age of patients was 29.5 +/- 4.8 years (range, 23-36 years).

Intervention: Metformin therapy, using 850 mg orally per day for 1 week.

Main Outcome Measure(s): Serum levels of T, FSH, and LH, fasting glucose/insulin ratio, levels of anti-Müllerian hormone (AMH) and inhibin B, and antral follicle count.

Result(s): Levels of AMH and inhibin B were statistically significantly higher in patients with PCOS compared to controls (2.81 +/- 1.79 ng/mL versus 0.95 +/- 1.17 ng/mL, and 56.24 +/- 29.39 pg/mL versus 17.89 +/- 12.87 pg/mL, respectively). Levels of AMH and inhibin B were similar among IR and NIR patients with PCOS (2.77 +/- 1.92 ng/mL versus 2.85 +/- 1.89 ng/mL, and 53.96 +/- 28.58 pg/mL versus 58.51 +/- 33.28 pg/mL, respectively). One week of metformin therapy did not alter either AMH or inhibin B levels. However, there was a statistically significant increase in glucose/insulin ratios (4.59 +/- 1.57 versus 6.35 +/- 3.6), and a significant decrease in the number of antral follicles after 1 week of metformin therapy (38.8 +/- 19.3 versus 23.1 +/- 7.4).

Conclusion(s): Levels of AMH and inhibin B are significantly increased in patients with PCOS compared to controls, but are not associated with insulin resistance. Low-dose metformin therapy improves IR and polycystic ovary morphology, even though levels of T, AMH, and inhibin B remain unchanged.