Ultrasound monitoring of ovarian structural changes has become a widely accepted method for the evaluation of ovarian function. The non-stimulated ovary of the early follicular phase shows a relatively homogeneous structure partly interrupted by small areas of ‘thinning’ (Figure 1). Regardless of whether ovulation is spontaneous or induced, the beginning follicular reaction is signalled by the appearance of small cystic-like structures, not yet persistently demonstrable from one day to the next (Figure 2). This discontinuous follicular reaction is paralleled by widely varying 17β-oestradiol concentrations and corresponds to the latent follicular phase defined by Insler and Lunenfeldl. Data from nine conception cycles in gonadotrophintreated women showed this phase to last 5–7 days, with a mean ± SE of 6.1 ± 0.26 days. It is followed by the phase of continuous follicular growth, which is to be expected as soon as one follicle has reached a size greater than 13 mm. (For a definition of size, see below.) This phase resembles the active follicular phase1 and lasted 4–7 days in the gonadotrophin-treated women, with a mean ±SE of 5.2 ± 0.32 days. Growth rates for the follicle are described ranging between 2.1 and 3.0 mm2–4.
KeywordsCorpus Luteum Follicular Phase Follicular Development Early Follicular Phase Conception Cycle
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