As far as the occurrence or non-occurrence of ovulation in the course of the ovarian cycles is concerned, women present both ovulatory ( biphasic ) and anovulatory ( monophasic ) cycles.

In the ovulatory cycles the complete follicular development takes place, resulting in the growth of a mature follicle, ovulation and formation of the corpus luteum. These cycles are considered biphasic because they present a follicular ( estrogenic ) and a luteal ( progesteronic-estrogenic ) phase. Along the follicular phase, the ovary produces mostly estrogens, while along the luteal one it produces progesterone and estrogens.

Conversely, in the anovulatory cycles obviously there is no ovulation and, as a consequence, the formation of the corpus luteum does not take place. In this way, these cycles are monophasic, since they exhibit only the follicular phase, which is characterized by variable degrees of persistent estrogen production.

As to the cases of "LUF" ( luteinized unruptured follicles ), we must remark that, despite also constituting a kind of failure in the ovulatory process, they must not be included in the usual category of anovulatory cycles because their histological and endocrine features differ too much from these ones, since these features are similar to those of the ovulatory cycles ( see Note 1, below ).

In this way, whenever I speak of anovulatory cycles I mean the specific kinds of ovarian and menstrual cycles that exhibit only the follicular phase, since in these cycles both ovulation and formation of the corpus luteum do not take place. Endocrinally and histologically they are monophasic cycles. Only follicles in variable stages of growth and involution can be found in the ovaries throughout these cycles.

Anovulatory cycles ( monophasic ) are physiologically normal soon after menarche, and are part of the process of maturation of the hypothalamus-pituitary-ovaries axis. This maturation is considered complete with the establishment of regular ovulatory cycles. Even so, we must remark that the occurrence of anovulatory cycles intermingled with the ovulatory ones is frequent and normal along the fertile years of a woman's life. In this way, we can say that there are women who ovulate more often, while others ovulate less often.

In the absence of hyperestrogenism, hyperprolactinemia, hyperandrogenic syndromes and the usually named "polycystic" pathologies of the ovaries, the occurrence of occasional anovulatory cycles with a regular duration intermingled with the ovulatory ones is considered normal ( see Note 2, below ).

We must also remark that, in the years that precede menopause, ovulation gradually becomes less frequent and even rare, and the anovulatory cycles predominate again. While in puberty the frequent occurrence of anovulatory cycles is due to the process of maturation of the hypothalamus-pituitary-ovaries axis, in pre-menopause the predominance of anovulatory cycles is a result of the progressive depletion and exhaustion of the ovaries.

There are the more varied possible patterns of follicular growth in the anovulatory cycles, with or without the formation of the mature follicle ( or follicle at the third stage of growth ). The duration of these cycles also may exhibit great variations, from the normal average of 25-32 days up to short cycles ( less than 25 days ) and long ones ( 35 to 50 days, or even more ). Therefore, there are several kinds of anovulatory cycles.

Though anovulatory cycles often tend to be irregular and exhibit variable patterns of follicular growth, there are also the common anovulatory cycles, characterized by the formation of a mature follicle ( or almost mature ) and duration within the limits of normality. Anovulatory cycles of this kind are relatively frequent throughout the menacme ( the period of women's lives in which they menstruate ) and, due to their characteristics, they are not perceived as such by women, who usually have no awareness of their occurrence. In practice, they only can be detected through a careful gynecologic study.

In these common anovulatory cycles the mature follicle may reach its usual size, but there is a failure in the ovulatory mechanism that results in the absence of the pituitary ovulatory peak of LH ( luteinizing hormone ). Because of this, there is no follicular rupture and the growing follicle persists as such for more 10 to 14 days, after which its process of follicular involution and atresia ( death ) begins. This results in the sudden fall of the estrogen levels and the consequent coming of menstruation.

Botella Llusiá remarks that in the common anovulatory cycles, "... the atresia and decay of the follicle takes place in such a way that the menstrual rhythm does not alter" ( "Tratado de Ginecologia, Tomo 3 - Enfermedades del Aparato Genital Femenino" - Editorial Científico-Médica, Barcelona, 1965 ). Nevertheless, there are also reports of regular anovulatory cycles in which signs of mature follicles cannot be detected.

On the other hand, long-lasting anovulatory cycles are often related to the prolonged persistence of mature follicles or to the usually named "polycystic" pathologies of the ovaries. Several endocrine disorders in the hypothalamus-pituitary-ovaries axis are responsible for chronic anovulation, long-lasting cycles ( oligomenorrhea ) and even amenorrhea.

It is also important to remark that, though many anovulatory cycles progress normally and without problems ( mostly those named common anovulatory cycles ), a considerable number of these cycles characterized by absence of ovulation tend to be associated with several degrees of relative or absolute hyperestrogenism, a condition that may cause endometrial hyperplasias. These endometrial hyperplasias, in turn, are very frequent causes of prolonged and/or excessive menstrual bleedings ( hypermenorrhea and/or menorrhagia ).

Chronic anovulation - which is different from the normal occurrence of some anovulatory cycles intermingled with the ovulatory ones - is obviously associated with infertility and, many times, with hyperestrogenism and endometrial hyperplasias. Endometrial hyperplasias require special medical attention in order to prevent a possible further development of endometrial cancer - though, fortunately, most of them are entirely benign and very frequent in the daily gynecologic practice. As I said above, the main clinical manifestations of endometrial hyperplasias are prolonged and/or excessive menstrual bleedings.

Note 1: There are cases of luteinization of follicles that do not ovulate, condition known as "LUF" ( luteinized unruptured follicles ). This is a very special sort of failure in the ovulatory process in which, despite the absence of follicular rupture and ovulation, the unruptured follicle becomes luteinized under the action of the LH ( luteinizing hormone ), giving rise to the corpus luteum. In such cases both the production of progesterone and the duration of the luteal phase of the cycle may be normal. Cases of "LUF" constitute, therefore, a very special kind of ovulatory failure with biphasic cycles.

Note 2: a) hyperestrogenism: excessive production of estrogens or excessive estrogenic activity; b) hyperprolactinemia: a disorder characterized by an excessive production of prolactin; c) hyperandrogenic syndromes: disorders characterized by an excessive production of androgens; d) as to the so-called "polycystic" pathologies of the ovaries ( "polycystic ovaries syndrome" ), I have some personal reservations regarding the use of the term "polycystic" for such disorders. I think they would be much better defined as "polymicrocystic ovaries." As to that condition, see my article "Polycystic Ovaries Syndrome".

Nelson Soucasaux is a gynecologist dedicated to Clinical, Preventive and Psychosomatic Gynecology. Graduated in 1974 by Faculdade de Medicina da Universidade Federal do Rio de Janeiro, he is the author of several articles published in medical journals and of the books "Novas Perspectivas em Ginecologia" ("New Perspectives in Gynecology") and "Os Órgãos Sexuais Femininos: Forma, Função, Símbolo e Arquétipo" ("The Female Sexual Organs: Shape, Function, Symbol and Archetype"), published by Imago Editora, Rio de Janeiro, 1990, 1993.

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