A couple’s fertility is periodic in nature. In men, it depends on the proper process of sperm production, the patency of the reproductive ducts, and the ability to engage in sexual intercourse. In women, fertility depends on the ability to engage in sexual intercourse, the capacity to conceive, to sustain and carry a pregnancy to term, and to give birth – and it is cyclical in nature.

The fertile window includes the lifespan of the egg released during ovulation (12-24 hours), as well as the period during which sperm can survive in the female reproductive tract (3-6 days in the presence of fertile cervical mucus; in contrast, when infertile‑type mucus is present, sperm viability is reduced to a maximum of about 3 hours).

Ovulation – the release of a single egg (and in rare cases more than one) — occurs only once in each menstrual cycle. The exact moment of ovulation is difficult to pinpoint. When analyzing the cycle, only indirect signs of the peri‑ovulatory period can be observed, such as the presence of clear, stretchy cervical mucus, softening and slight opening of the cervix, and changes in basal body temperature. The time considered most fertile, and closest to ovulation, is the mucus peak day and the following day, when a noticeable decline in mucus quality occurs. Some women also observe a sudden drop in basal body temperature (BBT) during the fertile period, followed by a rise to the higher‑temperature level. According to Prof. Rötzer, the day of this temperature dip and the first day of the temperature rise indicate the two most fertile days of the cycle.

It should be remembered that for ovulation to occur, a Graafian follicle mature enough to rupture must be present in the ovary, with a diameter of approximately 20–26 mm. However, the size of the developing follicle alone does not allow for precise determination of the moment of ovulation. The maturing follicle secretes estrogens, whose blood levels rise until they reach a peak approximately 24 hours before ovulation. Completion of follicular maturation leads to a decline in estrogen levels and triggers the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus, followed by the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). This so-called preovulatory gonadotropin surge is responsible for triggering ovulation, which usually occurs about 16 hours later. 

Numerous studies on the ovulation process (by Marik and Hulka, Kerin, Killick and Elstein, Craft, Tanger and Yovich, Rauscher and Ulm, Hilgers, Coulam) have identified a range of anomalies that may be responsible for so-called unexplained infertility, even when the menstrual cycle appears to be otherwise normal. These include:

• Luteinized unruptured follicle (LUF) – a Graafian follicle that fails to rupture, so the egg is not released, yet the follicle undergoes luteinization and transforms into a normally functioning corpus luteum.
• Ovum retention – a condition in which the Graafian follicle does rupture, but the egg is not released; instead, it remains trapped within the follicular wall and becomes enclosed in the forming corpus luteum.
• Empty follicle syndrome – development of a Graafian follicle without an egg and without a cumulus–oocyte complex.

Infertility is considered to be present when a desired pregnancy has not occurred after one to two years of regular attempts, without the use of any form of contraception.

Daily cycle observations provide very valuable information about a woman’s health, as well as about atypical or pathological conditions that may underlie fertility problems. Based on observations recorded on the cycle chart, it is possible to identify:

• absence of menstruation, prolonged menstrual bleeding, or intermenstrual bleeding;
• lack of a periovulatory rise in basal body temperature (a monophasic cycle), indicating absence of ovulation – although it should be noted that in polycystic ovary syndrome (PCOS) a temperature rise may occur despite ultrasound confirmation that no egg has been released;
• delayed ovulation;
• recurrent, difficult-to-interpret charts with unclear ovulatory signs;
• consistently elevated basal body temperature throughout the cycle, which may indicate hyperthyroidism;
• generally low basal body temperature levels, suggesting hypothyroidism;
• repeated luteal phases shorter than 10 days, indicating corpus luteum insufficiency (low progesterone levels) and a reduced ability to sustain pregnancy;
• a luteal phase (higher-temperature phase) lasting longer than 16 days despite a negative pregnancy test, which may suggest an ovulatory defect such as a luteinized unruptured follicle;
• failure to conceive despite clear signs of ovulation and appropriately timed intercourse;
• cycles with an excessively short mucus phase or the presence of only less fertile-type mucus (low estradiol levels), which is a common feature of infertile cycles;
• cycles with abnormal bleeding patterns, which are a particularly alarming sign and require prompt medical consultation and comprehensive diagnostic evaluation.

The recurrence of any of these abnormalities should always prompt consultation with a physician, who may order additional tests, initiate detailed outpatient diagnostics, and determine the most appropriate course of treatment.

The most common fertility problems in women are related to hormonal disorders. The key conditions include:

• Hyperprolactinemia – is an abnormally high level of prolactin, which may lead to reduced LH secretion during the periovulatory period, inhibition of ovulation, suppression of progesterone production, and an inability to sustain pregnancy. Hyperprolactinemia is not a disease in itself but a symptom, which is why identifying its underlying cause is essential.

Basic diagnostic tests include: serum prolactin (PRL) levels, TSH, T3, and T4 (to exclude primary hypothyroidism), urea or creatinine (to exclude renal insufficiency).

• Polycystic Ovary Syndrome (PCOS) – is a common hormonal disorder in women of reproductive age. Increasing attention is being paid to the role of elevated insulin levels in its pathogenesis. PCOS leads to excessive production of male androgens (including testosterone), which further increases the imbalance between LH and FSH – LH levels are elevated while FSH levels are reduced. As a result, the maturation of ovarian follicles is disrupted, ovulation is inhibited, follicles degenerate, and numerous cysts form along the periphery of the ovary. A characteristic symptom of this condition is infrequent, scant menstrual bleeding or secondary amenorrhea.

Basic diagnostic tests include: ovarian ultrasound, measurement of FSH and LH levels, TSH (to rule out hypothyroidism), and assessment of androgen levels.

• Luteal phase disorders – are associated with corpus luteum insufficiency, resulting in inadequate progesterone production. This leads to insufficient preparation of the endometrium for embryo implantation and a reduced ability to maintain pregnancy.

This disorder is easily detectable through basal body temperature (BBT) observation. In such cases, the second phase of the cycle (the luteal phase) is shortened and lasts less than 10 days.

• Thyroid disorders – both insufficient and excessive secretion of thyroid hormones cause systemic hormonal imbalance, which may result in anovulation, inadequate endometrial preparation for implantation, menstrual irregularities, or amenorrhea.

Basic diagnostic testing includes measurement of thyroid-stimulating hormone (TSH).

Anatomical causes of infertility are also relatively common:

• abnormal uterine structure or underdevelopment of the uterus,
• structural defects of the fallopian tubes.

Other causes include:

• Endometriosis – involves the displacement of fragments of the uterine lining (endometrium) that have not been shed into the abdominal cavity, where they implant and proliferate. This ectopic endometrial tissue behaves similarly to endometrium within the uterus – it undergoes cyclical changes and shedding, leading to bleeding, inflammation, and the formation of adhesions. Characteristic symptoms of endometriosis include prolonged, heavy, and painful menstruation, intermenstrual spotting, pain during intercourse, pelvic pain, and infertility.

Basic diagnostic tests include: ultrasound examination, measurement of the CA-125 marker in plasma, and laparoscopy.

• Immune system disorders (alloimmune and autoimmune causes) – in alloimmune infertility, a woman may produce antibodies against her partner’s sperm or develop hypersensitivity to certain components of the trophoblast, leading to constriction of the blood vessels supplying it and, consequently, death of the embryo nourished by the trophoblast. Autoimmune disorders may also occur, in which the immune system targets the woman’s own cells, potentially resulting in premature ovarian failure.
• Ovarian insufficiency – this condition refers to the depletion of the so-called pool of primary follicles in the ovaries (the ovarian reserve). It is important to note that in some cases, this condition may be temporary and immunologically mediated.

Basic examinations include: FSH level (above 30 U/L) and estrogen level (below 30 g/mL), AMH level, laparoscopy, and ovarian biopsy.

• Inflammatory and post‑inflammatory conditions of the reproductive organs – can lead to adhesions that hinder or prevent proper implantation of the embryo, cause blockage of the fallopian tubes or the cervix that makes fertilization impossible, and result in adhesions within the ovary, which can prevent ovulation. Uterine fibroids can cause similar complications. These are among the causes of female infertility.

By carrying out regular, daily observations of changes in basal body temperature and cervical mucus, and, if needed, performing self-examination of the cervix– you can, with relatively little effort, gain a clear understanding of your health. Most importantly, you can identify early health issues that may disrupt your fertility cycle. In many cases, this basic self-monitoring and early detection of potential abnormalities, followed by timely treatment, can prevent the progression of conditions that might otherwise lead to infertility. It also turns out that when menstrual cycle irregularities are detected early, simple measures may be sufficient: adopting healthier lifestyle habits, improving physical fitness, allowing the body adequate rest, and supplementing essential vitamins and minerals. These steps can significantly improve overall health and help restore a regular menstrual cycle.

The main causes of male fertility problems include:

• Hormonal disorders, most commonly low testosterone levels, which result in a reduced number of sperm produced.
• Varicocele (varicose veins of the spermatic cord), which causes a local increase in temperature around the testes, impairing sperm motility and potentially leading to sperm damage or death.
• Infections and inflammatory conditions – any inflammation of the male reproductive organs can damage sperm or even destroy the epididymis. A particularly dangerous condition is mumps, which can cause testicular damage in approximately 25% of males who contract the disease during puberty.
• Retrograde ejaculation, caused by impaired contraction of the urethral muscles, leading sperm to flow into the urinary bladder instead of being expelled through the urethra. This condition may be temporary or permanent.
• Cancers of the reproductive organs and their treatment, which often result in permanent infertility. In some cases, however, spermatogenesis may partially recover several years after treatment ends.
• Unhealthy lifestyle factors – the use of stimulants (such as alcohol or drugs), poor diet, and chronic stress can reduce sperm count, motility, and viability. Prolonged overheating of the testicular area (including wearing tight underwear) can also impair sperm production.
• Certain systemic diseases, such as cardiovascular disorders, chronic kidney disease, diabetes, anemia, pancreatic and liver diseases, alcoholism, or pelvic infections, may also contribute to reduced male fertility.

Medicinal preparations most commonly used in Natural Family Planning (NFP) and NaProTechnology:

For women:

• Magnesium – used to help regulate the menstrual cycle; it can shorten excessively long menstrual bleeding, relieve menstrual pain, reduce an overly long mucus phase, ease uterine cramps, and decrease nervousness and susceptibility to stress.
• Herbal preparations based on chaste tree fruit (Vitex agnus-castus) – used to regulate the menstrual cycle by lengthening the second (luteal) phase; they also help lower elevated prolactin levels and alleviate symptoms of premenstrual syndrome (PMS) and migraine headaches.
• Evening primrose oil – used to improve both the quality and quantity of cervical mucus and to help relieve PMS-related symptoms.
• Vitamin B6 – used to improve the quality and amount of cervical mucus and to support lengthening of the second phase of the cycle.
• Progestogen therapy (progesterone supplementation) – used for 10-12 days in cycles in which ovulation and the high-temperature phase do not occur. This therapy must be carried out under close medical supervision and tailored to the individual cycle pattern. It usually begins on the fourth day after the mucus peak. After three days of treatment, infertility associated with increased progesterone levels occurs and lasts until the end of the cycle. Important: not all progesterone preparations are suitable for this therapy, as some do not induce a high-temperature phase.

For men:

• Natural supplements supporting spermatogenesis, semen quality, and male reproductive function. These typically contain various combinations of: L-carnitine fumarate, acetyl-L-carnitine, beta-carotene, vitamin C, coenzyme Q10, zinc, folic acid, selenium, B-group vitamins (especially B12), copper, chromium, and vitamins A and E.

It should be remembered that spermatogenesis – the process of sperm production and maturation – takes as long as 10 weeks in men. Therefore, steps to improve semen quality should begin even 3 months before attempting to conceive.