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Evaluation of the menstrual cycle and timing of ovulation

Evaluation of the menstrual cycle and timing of ovulation
Literature review current through: May 2024.
This topic last updated: Sep 20, 2023.

INTRODUCTION — There are a number of settings in which evaluation of the menstrual cycle may be important. A common question is whether a particular female ovulates, an issue that can arise in a number of different settings.

The detection and timing of ovulation will be reviewed here. The sequence of events occurring in the normal menstrual cycle, with a detailed description of the different phases, is discussed separately (see "Normal menstrual cycle"). A discussion of female infertility is found elsewhere. (See "Overview of infertility".)

ASSESSMENT OF OVULATION — Ovulation assessment/prediction is important to time intercourse for pregnancy, especially in females who are having trouble conceiving. Females with irregular cycles or heavy, painful menses are appropriate candidates for evaluation/detection of ovulation (eg, is anovulation the underlying cause of their symptoms?) (table 1). (See "Female infertility: Causes", section on 'Ovulatory disorders' and "Abnormal uterine bleeding in nonpregnant reproductive-age patients: Terminology, evaluation, and approach to diagnosis", section on 'Irregular bleeding'.)

There are several ways to evaluate the function of the hypothalamic-pituitary-ovarian axis in females, each with different costs and timeframes. They also address different issues, such as detection of the presence of ovulation and detection of the timing of ovulation. Menstrual cycle charting, basal body temperature monitoring, and measurement of the serum progesterone concentration can be used to answer whether ovulation has occurred, while measurement of follicle size and the luteinizing hormone (LH) surge in serum or urine kits, along with other technologies, can be used to detect the timing of ovulation.

Methods to detect ovulation

Menstrual cycle charting — The simplest and least expensive method is menstrual cycle charting. This involves recording the days of onset and cessation of menses for several months in succession. Menstrual cycles between 25 and 35 days are generally ovulatory. Shorter cycles may occur owing to a shortening of the follicular phase, as occurs in aging. Longer and shorter cycles may also indicate anovulation.

The patient should also note molimina symptoms, which can be a useful clinical indicator of normal reproductive hormone cycling. These symptoms include an increase in thin cervical mucus secretions noted at mid-cycle and typical premenstrual symptoms, such as menstrual cramps, breast tenderness, fluid retention, and appetite or mood changes.

Basal body temperature monitoring — Progesterone released from the corpus luteum after ovulation (figure 1) has potent effects on the hypothalamus, one of which is to increase body temperature. As a result, daily temperature monitoring can be used to document progesterone production and, therefore, ovulation.

This technique requires the use of a special basal body temperature thermometer, which typically has units from 96 to 100 degrees, so that each one-tenth of a degree is easily distinguishable. We recommend the use of a mercury thermometer, obtainable from any pharmacy. In our experience, current electronic thermometers are not sufficiently accurate for detection of the postovulatory temperature rise.

The female takes her temperature by putting the thermometer under her tongue every morning while she is still in the basal state. This means before she gets out of bed, uses the bathroom, or has anything to eat or drink. Although there is an expected amount of variability with daily use of the thermometer, an approximately 0.5°F rise in body temperature can be detected in the luteal phase of the menstrual cycle compared with the follicular phase. In a normal cycle, the temperature rise begins one or two days after the LH surge and persists for at least 10 days. Thus, temperature changes are sufficient to retrospectively identify ovulation, but they occur too late to be useful for timing sexual intercourse to conceive. The subsequent fall in basal body temperature can be used as an indicator of the imminent onset of menses.

Serum progesterone concentration — Another simple test is measurement of the serum progesterone level in the mid-luteal phase, 18 to 24 days after the onset of menses or seven days before the next menses are expected (see "Normal menstrual cycle", section on 'Midcycle surge and ovulation'). Normal mid-luteal phase progesterone levels are between 6 and 25 ng/mL. When a progesterone level is low (eg, 2 ng/mL), one option is to repeat the test in two to three days. If it is not rising, it likely indicates a luteinized, unruptured follicle. These follicles are partially luteinized and make progesterone, but they do not have a sufficient cell number or synthetic ability to make adequate progesterone to support the luteal phase.

There is considerable variability in single blood samples for progesterone because progesterone levels can increase in response to LH pulsations occurring after ovulation (figure 2) [1]. Thus, a single low value cannot reliably detect an abnormal luteal phase, since it may be obtained between LH pulses. In comparison, a single level above 6 ng/mL is usually indicative of normal corpus luteum function.

Predicting ovulation — For couples pursuing pregnancy, the highest probability of conception appears to be with intercourse one to two days prior to ovulation (see "Unexplained infertility"). Therefore, attempting to identify the fertile period and timing intercourse during this interval maximizes the probability of conception. This can be inferred by comparing the results of the following studies: the first series consisted of 100 fertile couples who conceived without timed intercourse and reported pregnancy rates of 50 percent at 3 months, 75 percent at 6 months, and over 90 percent at 12 months, whereas a second series of similar couples who used a method of fertility awareness with timed intercourse observed pregnancy rates of 76 percent at 1 month and 100 percent at 7 months [2].

Identifying the fertile period — Calendar and basal body temperature methods are not very reliable for identifying the fertile period, because of normal variation in cycle length and because the temperature rise associated with ovulation occurs too late to be useful [2]. Better alternatives are methods that have the female examine her vaginal discharge for changes suggestive of a preovulatory estrogen effect, such as an increased volume of clear, stretchy, slippery mucus. Measurement of urinary luteinizing hormone (LH) and/or estrogen is more expensive but also effective. Newer technologies include changes in saliva, vaginal mucous or temperature. These methods are discussed here and outlined (table 1).

Conventional methods

Measurement of LH surge and estradiol rise — The luteinizing hormone (LH) surge can be detected in either urine or serum samples. Urinary LH kits are commercially available for home use and are helpful for many females. The LH surge appears in the urine within 12 hours after it appears in the serum; as a result, it can accurately predict ovulation and, therefore, the optimal time for intercourse. The rise in serum LH typically occurs approximately 36 hours before the oocyte is released from the follicle into the fallopian tube. Females typically begin testing their urine one or two days before the expected surge, so that the increase over baseline levels can be clearly observed.

Digital and electronic monitors have been developed that monitor both the estradiol and LH rise in urine to predict ovulation more precisely. These monitors identify more fertile days before and including the ovulation day by detection of the estrogen rise before the LH surge as well as the LH surge.

The urinary LH kit instructions must be followed precisely as different kits are standardized to different times of the day. In addition, the urine kit should probably be used only after ovulation has previously been documented. Any condition associated with elevated LH levels, such as polycystic ovary syndrome (PCOS), primary ovarian insufficiency, and menopause, can yield false-positive results despite the absence of ovulation. Adding the estradiol rise to the prediction may help decrease false-positive results. Patients should be instructed in correct use of the kit as false-positive interpretation of the LH surge occurs in 7 percent of cycles (table 1) [3].

In contrast, there is little utility for serum LH measurements in conventional practice, except for females preparing for in vitro fertilization. Use of serum measurement requires very precise knowledge of normal LH ranges in the immunoassay used, and there is considerable variability in assay results depending upon antibodies, standards, and techniques [4]. In addition, there are high amplitude LH pulses at the surge leading to considerable hour-to-hour variability.

Pelvic ultrasonography — Identification of a peri-ovulatory follicle on ultrasonography is another important tool for evaluating the menstrual cycle and ovulation, although it is not used routinely for timing of intercourse, given its expense. Ultrasonography can identify a large follicle as a round cystic structure that reaches a diameter of 16 to 30 mm prior to rupture and release of the oocyte.

There are two methods currently in use. The transabdominal approach requires a full urinary bladder as an echo-free window through which to observe the complete pelvis and its organs. The transvaginal approach uses a vaginal probe transducer. Due to its closer proximity to the internal organs, the vaginal probe achieves a higher resolution and avoids the requirement for a full bladder. Therefore, the transvaginal approach is generally preferred by females while the transabdominal approach is usually reserved for girls, sexually inactive females, and cases in which a complete survey of the pelvis is important.

The average pre-ovulatory follicle is between 20 and 25 mm in diameter before rupture, depending partly upon the observer's technique. Ultrasound is most useful when performed serially. The detection of a large cyst at any one time is insufficient to establish that it is a normal dominant follicle, unless preceded one week earlier with a scan demonstrating no large follicles, associated concurrently with an appropriately elevated serum estradiol level, or followed one week later with a scan showing a collapsed follicle in the same location with internal echoes consistent with its transformation to a corpus luteum. The last option may be preferable in females in whom there is a suggestion of low luteal-phase progesterone levels, raising the possibility of anovulation with luteinization of the unruptured follicle.

The simultaneous appearance of the endometrium may also be useful in establishing the functionality of an observed cyst. A thick proliferative endometrium suggests active estradiol secretion and a brightly echogenic endometrium (due to changes in gland structure) suggests appropriate progesterone production in the luteal phase.

Additional approaches

Salivary ferning — Saliva forms a pattern that looks like a fern when the saliva dries around the time of ovulation. Microscopes and slides can be purchased to look for salivary ferning. The accuracy of salivary ferning is lower than for other methods (table 1).

Temperature sensors — Vaginal and underarm temperature sensors that takes thousands of measurements throughout the day and night and reports temperature data to a server. The temperature data are used to predict ovulation (table 1).

Smartphone-based detection — Smartphone apps can increase the chance of predicting ovulation by combining data from temperature, urine, or salivary measurements, as described above. New technology may even incorporate ultrasound to detect ovulation.

OVARIAN RESERVE — A final test in the evaluation of the menstrual cycle, especially in older or infertile females, is assessment of ovarian reserve. This can include measurement of an early follicular phase (EFP) serum follicle-stimulating hormone (FSH) and estradiol level. The utility of this test derives from the gradual changes in gonadotropin levels that occur across the menstrual cycle as females age (see "Ovarian development and failure (menopause) in normal women"). In particular, as the follicular phase shortens prior to menopause, EFP FSH levels increase before any detectable fall in peak estradiol or progesterone levels, or in luteal phase length [5].

A more detailed discussion of ovarian reserve, including anti-müllerian hormone, inhibin B concentrations, and ultrasound assessment of antral follicle count, are reviewed separately. (See "Female infertility: Evaluation", section on 'Assessment of ovarian reserve' and "In vitro fertilization: Procedure", section on 'Assessment of ovarian reserve' and "Advancing maternal age: Infertility evaluation and management", section on 'Diminished ovarian reserve'.)

SUMMARY

Assessment of ovulation – In a female with irregular menstrual cycles, excessive bleeding, or infertility, it is important to determine whether she is ovulating. (See 'Assessment of ovulation' above.)

Methods to detect ovulation

Menstrual cycle charting – Menstrual cycles between 25 and 35 days are generally ovulatory. (See 'Menstrual cycle charting' above.)

Basal body temperature monitoring – A rise in basal body temperature of 0.5°F can be detected when the progesterone rises after ovulation. (See 'Basal body temperature monitoring' above.)

Serum progesterone concentration – A serum progesterone level of 6 to 25 ng/mL drawn seven days before menses is a reliable indicator of ovulation. (See 'Serum progesterone concentration' above.)

Methods to detect timing of ovulation – The day of ovulation can be determined in the fertile period (approximately 14 days before the expected day of menses) using an ovulation predictor kit or ultrasound measurement of follicle size. (See 'Predicting ovulation' above.)

Assessment of ovarian reserve – An early follicular phase (EFP) follicle-stimulating hormone (FSH) level, paired with an estradiol level, can help predict ovarian reserve if the assay used has been validated at the facility where it is used. (See 'Ovarian reserve' above.)

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