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Chapter 1
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produced by these growing follicles, FSH concentrations start to decrease in the mid to
late follicular phase. This decremental FSH limits the time that the FSH concentration
is above the FSH threshold and seems essential for single dominant follicle selection.
Despite this decline in FSH, the most mature follicle continues its growth by increased
sensitivity for FSH stimulation. All other recruited follicles lack sufficient FSH stimulation
and enter atresia. The “FSH gate” (Baird, 1987) or “FSH window” (Fauser et al.,
1993) concept adds the element of time to the FSH threshold theory and emphasizes
the importance of a transient increase of FSH above the threshold level in order to gain
single dominant follicle selection (Figure 1.3).
1.3. Disturbed folliculogenesis
Figure 1.3 The threshold/window concept. Decremental FSH concentration seems essential for
single dominant follicle selection.
Anovulation represents a major cause of female reproductive dysfunction and can be
identified in 18-25% of couples presenting with infertility (Laven et al., 2002). Menstrual
cycle disturbances (oligomenorrhoea or amenorrhoea) are usually a reflection
of hormonal dysbalance and disturbed folliculogenesis. Whether and how frequently
these occasional bleedings are associated with preceding ovulatory cycles is unknown.
Obviously, induction of ovulation is required in these anovulatory patients to achieve
follicular maturation, subsequent ovulation and ultimately conception.
The clinical approach to ovulation induction in patients with ovarian dysfunction
requires understanding of the causes of anovulation. Patients presenting with oligomenorrhoea
or amenorrhoea are usually categorized into 3 main categories, referred to as
WHO (World Health Organization) classification group 1, 2 and 3 (Rowe et al., 2001).