Antral follicle counts by transvaginal ultrasonography are related to age in women with proven natural fertility

Objective: To investigate the relation between reproductive age and ultrasound (US)-based follicle counts and the reproducibility of follicle counts in regularly cycling women with proven fertility. Design: Prospective observational study. Setting: Tertiary fertility center. Patient(s): Healthy female volunteers with proven fertility, recruited by advertisement in local newspapers. Intervention(s): The number of antral follicles sized 2-10 mm and ovarian volume were estimated by transvaginal US in the early follicular phase of the menstrual cycle in 162 women. A subgroup of 81 women underwent transvaginal US at several times in three subsequent cycles. Main Outcome Measure(s): Antral follicle count and total ovarian volume. Result(s): Women aged 25-46 years (n = 162) were studied. The relation of age with the US indices was computed after natural log transformation. Antral follicle count showed the dearest correlation with age (R = -0.67). A biphasic linear model gave the best fit to the data. Before the age of 37 years, the antral follicle count showed a mean yearly decline of 4.8%, compared with 11.7% thereafter. The reproducibility of the antral follicle count in two subsequent cycles was moderate. Conclusion(s): The number of small antral follicles in both ovaries as measured by US is clearly related to reproductive age and could well reflect the size of the remaining primordial follicle pool. (Fertil Steril(R) 1999; 72:845-51. (C) 1999 by American Society for Reproductive Medicine.)